Symposium Organizers
Sheng Dai Oak Ridge National Laboratory
Harold H. Kung Northwestern University
Jun Liu Pacific Northwest National Laboratory
Chung-Yuan Mou National Taiwan University
Monday PM, November 30, 2009
Room 311 (Hynes)
9:30 AM - **Y1.1
Molecular-scale Catalysts on Solid Supports: Synthesis, Structure Determination, and Design.
Bruce Gates 1
1 Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, California, United States
Show AbstractThe typical industrial catalyst is a highly nonuniform set of nano-structures dispersed on a porous, nonuniform support. In contrast, some supported catalysts, such as those used for olefin polymerization, are much more nearly uniform, being molecular in character and offering the prospective advantages of molecular catalysts in solution, such as high selectivity. Our goals were to gain a deeper understanding of the class of supported metal catalysts with virtual molecular structures. We report results characterizing single-metal-atom complexes as well as clusters that consist of only a few atoms each, with metals selected from groups 6, 7, and 8. The catalysts are synthesized by the reactions of organometallic compounds with support surfaces followed by treatments to modify or remove the ligands on the metals and ensure bonding of the metals to the supports. Understanding of the structures and properties of these materials emerges from complementary spectroscopic and microscopic techniques; the most incisive methods are infrared and X-ray absorption spectroscopies and high-resolution transmission electron microscopy, all combined with density functional theory. Results are presented for complexes and clusters of tantalum, rhenium, ruthenium, osmium, iridium, and gold. For example, gold on MgO was prepared from the precursor Au(CH3)2(acac) [acac is C5H7O2], giving isolated gold complexes with each Au atom bonded to two oxygen atoms of the MgO; the individual Au atoms have been imaged with STEM. Spectroscopic data determine the processes of formation and breakup of clusters of metal, illustrated by rhodium and iridium, on supports. Elucidation of the detailed structures and reactivities points the way to the preparation of supported catalysts with specific and essentially molecular structures as a basis for tuning the catalytic properties.
10:00 AM - Y1.2
Metal Nanoparticles: From their Organometallic Synthesis to their Application in Catalysis.
Karine Philippot 1 , Bruno Chaudret 1
1 Laboratoire de Chimie de Coordination, CNRS, Toulouse France
Show AbstractMany efforts are devoted to the synthesis of metals or metal oxides nanomaterials. This interest comes from their attractive properties that can find applications in various areas1 such as catalysis.2In our group, the synthesis of metal and metal oxide nanoobjects is performed through an organometallic approach.3 Metal organic complexes are decomposed in solution under mild conditions and in the presence of stabilizing agents like simple long alkylchain ligands (alcohols, amines, diphosphines) or more sophisticated ones (diphosphites, oxazolines). Depending on the reaction conditions nanoobjects of tuneable characteristics are formed, the control of which is possible since the reaction parameters have an influence on the nucleation step and/or the growth step of the nanoparticles synthesis. Our objective is to obtain well-dispersed nanoparticles with a narrow size distribution, a controlled shape and a controlled surface composition, all these parameters being important for further applications. This method is reproducible and can be applied for a large variety of metals (Ru, Rh, Pt, Pd) as well as for metal oxides (RuO2, SnO2). This approach can also lead to nanoparticles deposited into supports like mesoporous silica4 or carbon nanotubes.5Examples of so-obtained nanomaterials will be presented. A particular attention will be devoted to their surface reactivity6 that can lead to applications in the field of catalysis like in aromatic compounds hydrogenation7 or enantioselective allylic alkylation8 or as catalytic filters for gas sensors.4,9References:1Nanoparticles, from theory to applications, Schmid, G. (Ed.), Wiley-VCH: Weinheim, 20042Nanoparticles and Catalysis, Wiley-VCH, Weinheim, (Ed D. Astruc), 20083Organometallic Derived–I: Metals, Colloids and Nanoparticles, K. Philippot and B. Chaudret, Comprehensive Organometallic Chemistry III, Elsevier, Vol. 12, Dermot O'Hare (Volume Ed.), 2007, 714S. Jansat, K. Pelzer, J. García-Antón, R. Raucoules, K. Philippot, A. Maisonnat, B. Chaudret, Y. Guari, A. Medhi, C. Reyé, R.J.P. Corriu, Adv. Funct. Mater, 2007, 17, 33395E. Castillejos, P.-J. Debouttière, L. Roiban, A. Solhy, V. Martinez, Y. Kihn, O. Ersen, K. Philippot, B. Chaudret, P. Serp, Angew. Chemie Int. Ed., 2009, 48, 25296J. García-Antón, M. Rosa Axet, S. Jansat, K. Philippot, B. Chaudret, T. Pery, G. Buntkowsky, H.-H. Limbach, Angew. Chem. Int. Ed., 2008, 47, 20747A. Gual, M. Rosa Axet, K. Philippot, B. Chaudret, A. Denicourt-Nowicki, A. Roucoux, S. Castillón and C. Claver, Chem. Commun, 2008, 27598I. Favier, M. Gómez, G. Muller, R. Axet, S. Castillón, C. Claver, S. Jansat, B. Chaudret, K. Philippot, Adv.Synth.Catal., 2007, 349, 24599V. Matsura, Y. Guari, C. Reyé, R. J.P.Corriu, M. Tristany, S. Jansat, K. Philippot, A. Maisonnat, B. Chaudret Adv. Funct. Mater. 2009 in press
10:15 AM - Y1.3
Synthesis of Ru Nanoparticles in Ionic Liquids Applications in Catalysis.
Gorka Salas 1 , Georgina Fraser 2 , Paul Campbell 2 , Karine Philippot 1 , Catherine Santini 2 , Bruno Chaudret 1
1 Nanostructures and Organometallic Chemistry, Laboratoire de Chimie de Coordination, Toulouse France, 2 , Laboratoire de Chimie Organométallique de Surface (CNRS), Lyon France
Show AbstractThe use of nanoparticles as catalysts is a topic of growing interest thanks to its strategic location in the frontier between homogeneous and heterogeneous catalysis. While homogeneous catalysts are generally difficult to take away from the reaction products, but are by far highly selective and efficient, heterogeneous ones are easily separated from the reaction mixtures and generally do not suffer because of high reaction temperatures.1 This is probably the main reason because of which heterogeneous catalysis is more extensively applied for industrial applications. The development of nanocatalysts is expected to overcome the disadvantages of both kinds of catalysts while keeping their advantages.On the other hand, ionic liquids have emerged as an environmentally friendly alternative to the use of common organic solvents. They are non-volatile compounds and good solvents for both organic and inorganic compounds.2 The most widely used are imidazolium based ionic liquids, which are easy to prepare, and whose physico-chemical properties can be tuned by simple changing the anion or the substituents bonded to the imidazolium cation.In this context, our objective is to develop new catalytic systems based on the preparation of well-controlled nanoparticles into ionic liquids.3 Thus, the synthesis and the characterization of ruthenium nanoparticles in various imidazolium based ionic liquids will be described. They are prepared by H2 reduction of the organometallic precursor [Ru(COD)(COT)] (COD = 1,5-cyclooctadiene; COT = 1,3,5-cyclooctatriene) in mild conditions (3 bar H2, 30 °C) and display very small mean size (1-2 nm) with narrow size distributions that make it them very interesting catalytic systems.4 The so-obtained colloidal suspensions have been used in the catalytic hydrogenation of aromatic compounds, which undergo through heterogeneous catalysis, but not through homogeneous one.51 Astruc, D. in Nanoparticles and Catalysis; Astruc, D., Ed.; Wiley-VCH: Weinheim, Germany, 2008; Chapter 1.2 Welton, T. Chem. Rev. 1999, 99, 2071-2084.3 (a) Gutel, T.; Garcia-Anton, J.; Pelzer, K.; Philippot, K.; Santini, C. C.; Chauvin, Y.; Chaudret, B.; Basset, J. M. J. Mater. Chem. 2007, 17, 3290-3292; (b) Gutel, T.; Santini, C. C.; Philippot, K.; Padua, A.; Pelzer, K.; Chaudret, B.; Chauvin, Y.; Basset, J. M. J. Mater. Chem. 2009, 19, 3624-3631.4 Duteil, A.; Quéau, R.; Chaudret, B.; Mazel, R.; Roucau, C. Chem. Mater. 1993, 5, 341-347.5 (a) Hagen, C. M.; Vieille-Petit, L.; Laurenczy, G.; Süss-Fink, G.; Finke, R. G. Organometallics 2005, 24, 1819-1831; (b) Astruc, D.; Lu, F.; Aranzaes, J. R. Angew. Chem. Int. Ed. 2005, 44, 7852-7872; (c) Dyson, P. J. Dalton Trans. 2003, 2964-74; (d) Widegren, J. A; Finke, R. G. J. Mol. Catal. A: Chem. 2003, 198, 317-341.
10:30 AM - Y1.4
Preparation of High-Quality Pt-Cu Nanocubes with Enhanced Electrocatalytic Activity towards Methanol Oxidation Reaction.
Dan Xu 1 , Hongzhou Yang 2 , Shouzhong Zou 2 , Jiye Fang 1
1 Chemistry, State University of New York at Binghamton, Binghamton, New York, United States, 2 Chemistry and Biochemistry, Miami University, Oxford, Ohio, United States
Show AbstractPt-based alloy nanoparticles are frequently used as efficient catalysts for fuel cell reactions because the presence of the second metal often increases their catalytic activity and stability. For many reactions, the catalytic activity of particles depends on the atomic arrangement of their surfaces. It is therefore important to control the particle shape. However, preparation of monodisperse nanopolyhedra of Pt-based bimetals is rather challenging. In this presentation, we report a new strategy of wet-chemical synthesis of Pt-Cu nanocubes as well as their shape evolution. We successfully prepared high-quality Pt–Cu nanocubes by co-reduction of platinum(II) acetylacetonate ([Pd(acac)2]) and copper(II) acetylacetonate ([Cu(acac)2]) using 1,2-tetradecanediol (TDD) in 1-octadecene (ODE) as the solvent, which also contained tetraoctylammonium bromide (TOAB), oleylamine (OLA), and a trace amount of 1- dodecanethiol (DDT). All of the synthetic parameters, such as the OLA/TOAB ratio as well as the amounts of DDT and TDD, were fully optimized. The mechanism of nucleation and nanocrystal growth is explored and discussed based on the observation of the intermediate nanoparticles when some of the reaction parameters were precisely tuned. The electrocatalytic activity of these Pt–Cu nanocubes towards methanol oxidation is also evaluated in comparison with that of spherical Pt–Cu nanocrystals and Pt nanocrystals with similar sizes. The Pt–Cu nanocubes demonstrate a superior electrocatalytic activity towards methanol oxidation to those with mixed crystallographic facets.
10:45 AM - Y1.5
Catalytic Performance of Nanostructured Plate-type Cu and Cu-Fe on ZnO Nanorods for Steam Reforming of Methanol.
Chien-Cheng Li 1 , Ran-Jin Lin 2 , Li-Chyong Chen 1 , Kuei-Hsien Chen 3
1 Center for Condensed Matter Sciences, National Taiwan University, Taipei, 10617, Taiwan, 2 , Intellectual Property Exchange Limited, Hsinchu, 310, Taiwan, 3 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
Show AbstractTwo types of proton-exchange membrane fuel cells (PEMFC) systems are using liquid hydrocarbon sources: the direct methanol fuel cell (DMFC) and the reforming methanol fuel cell (RMFC). For RMFC system, the electrical energy was generated using concentrated hydrogen produced by steam reforming of methanol (SRM). SRM is a promising route to produce hydrogen and thus an attractive power source for on-board or portable devices. Cu-based materials are well known as most active catalysts for SRM. However, traditional CuO/ZnO or CuO/ZnO/Al2O3 catalysts have low thermal and durability above 300°C. Therefore, the development of stable catalysts with high activity and selectivity is required. The stability and activity of the Cu-based catalysts are strongly related to the additive metals, composition, dispersion of Cu, methods of catalyst preparation, surface area, and microstructure of the catalysts. In this study, nanostructured plate-type Cu and Cu-Fe catalysts have been successfully prepared by electroless plating on ZnO nanorods/stainless steel substrates. The plate-type Cu and Cu-Fe catalysts are composed of nanocrystalline crystals. The size of the nanocrystalline crystals is about 10 to 25 nm. The results show that the catalytic activity of the plated Cu-Fe catalysts was improved by adding Fe to plated Cu catalysts. The addition of Fe to plated Cu catalysts has promoted the dispersion and reducibility of CuO. The temperature of reduction of the plated Cu-Fe catalyst is a narrow peak in the range of 125°C to 175°C. However, the plated Cu catalyst is a board peak in the range of 125°C to 250°C. The plated Cu-Fe exhibits higher catalyst durability since Fe effectively inhibited the sintering of copper at high temperatures. The detailed results about the effects of chemical composition and reaction temperature of the plated Cu and Cu-Fe catalysts on their durability in steam reforming of methanol were investigated.
11:30 AM - **Y1.6
Design of Amphiphilic ABC Triblock Copolymer for Templating Synthesis of Large-pore Ordered Mesoporous Carbons with Tunable Pore Wall Thickness.
Dongyuan Zhao 1
1 , fudan university, Shanghai China
Show AbstractAbstract: We demonstrate a successful synthesis of highly ordered mesoporous carbons with large pores and tunable pore walls by using a home-designed ABC amphiphilic triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) with gradient hydrophilicity as a template, resol as a carbon source, via the solvent evaporation induced self-assembly (EISA) strategy. The obtained carbon products possess ordered face-centered cubic (fcc) close-packed (Fm3m) mesostructure with large pores of about 20.0 nm. By simply adjusting the resol/template ratios, the wall thickness of products can easily be tuned in the range of 10 – 19 nm. For the first time, we observed numerous large micro/mesopores in the carbon pore walls, originating from the removal of PMMA segment during the pyrolysis. The obtained mesoporous carbons have an extra-large lattice constant of up to 55.0 nm, high surface areas of ~ 900 m2/g and pore volume of ~ 0.6 cm3/g, as well as high stability even in concentrated KOH solution. Introduction: Ordered mesoporous carbon materials have attracted increasing attention for their unique properties and great potential for applications in various fields, such as adsorption and separation, catalysis, electrochemistry and sensorics.[1-3] The reported highly ordered mesoporous carbons are usually obtained by using two-component amphiphilic block copolymers as templates including PEO-PPO-PEO, PEO-PS and PEO-PMMA block copolymers [4-6]. Compared with AB or ABA block copolymers, amphiphilic ABC triblock copolymers are more adaptive candidates as the templates for the creation of novel mesoporous materials with designable structures, compositions, and tunable pore/wall parameters. Herein, we designed an amphiphilic ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO125-b-PMMA100-b-PS138) with gradient hydrophilicity prepared by the simple method of atom transfer radical polymerization (ATRP).[31] By using this ABC-type triblock copolymer as a template, we have successfully synthesized highly ordered mesoporous carbons with large pores (up to 20 nm) via an EISA method in tetrahydrofuran as the solvent. The obtained carbon products possess ordered face-centered cubic (fcc) close-packed (Fm3m) mesostructure with super-large lattice constant of up to 55.0 nm. By simply adjusting the resol/template ratios, the carbon wall thickness can easily be tuned in the range of 10 – 19 nm. A multitude of large micro/mesopores (around 2 nm) in the carbon walls is, for the first time, clearly observed by HRSEM images.
12:00 PM - Y1.7
Towards the Rational Design of Supported-Bimetallic Nanoparticle Catalysts.
Robert Scott 1 , Priyabrat Dash 1
1 Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
Show AbstractHeterogeneous catalysts consisting of nanoparticles dispersed on an oxide support are a mainstay in industrial reactions, and are often made via thermal reduction of metal salts dispersed onto a pre-synthesized support. In this talk I will document routes developed in our laboratory to design xerogel supported-nanoparticle catalysts by trapping pre-synthesized, structurally controlled polymer-stabilized bimetallic nanoparticle precursors into sol-gel matrices. Such routes allow for the tuning of the size, structure, architecture, and electronic properties of the nanoparticle catalysts, which can allow for the development of highly efficient and selective catalysts. As proof of concept I will document work in our group detailing the synthesis of co-reduced and core-shell nanoparticles on xerogel supports. The final materials have been fully characterized by TEM, energy dispersive spectroscopy (EDS), thermal analysis, and x-ray absorption spectroscopy (EXAFS, XANES). HRTEM, EDS line-scan, and EXAFS results confirm the compositional and structural homogeneity of the final support-nanoparticle materials, and XANES spectra allow catalytically-relevant electronic interactions between the metals to be probed. Finally, I will show that the resulting materials can be used as extremely active and selective catalysts for a wide range of reduction and oxidation reactions as well as extremely selective gas sensors.
12:15 PM - Y1.8
Immobilization of High Temperature Biocatalysts on Nanofibrous Supports.
Christina Tang 1 , Carl Saquing 1 , Sindhura Sevala 1 , Stephen Morton 1 , Robert Kelly 1 , Saad Khan 1
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractA variety of processing techniques can be improved by incorporating enzymes into industrial practices including production of sweeteners from corn starch, soy food processing, and paper bleaching. Enzymes are highly efficient selective biological catalysts and their immobilization can improve their functionality and stability for bioprocessing applications. Immobilization on nanofibrous materials is advantageous due to high surface area to mass ratios. Hyperthermophilic enzymes are of particular interest because they have optimal catalytic activity at high temperatures common to industrial processes. Electrospinning is a simple technique used to generate nanofibrous membranes for enzyme immobilization. We have electrospun aqueous solutions of polyvinyl alcohol (PVA) and a model hyperthermophilic enzyme, α-galactosidase from Thermotoga maritima , to generate nanofibers between 150 and 200 nm in diameter with immobilized enzyme. A maximum enzyme loading of 0.5 % (5 mg enzyme/g PVA) has been achieved. The critical polymer concentration for achieving uniform fibers has been determined, as well as the effect of increasing enzyme loading (weight enzyme/weight of polymer) on solution rheology and fiber size. The enzyme loaded PVA fibers have been chemically crosslinked by exposure to glutaraldehyde (GA) vapor, to make the fibers water-insoluble. After crosslinking, the fibrous structure remains intact and the enzyme retains catalytic activity. However, the enzyme activity of the immobilized enzyme was about 10 fold lower than the free enzyme. The activity as a function of temperature and thermal stability of the enzyme was also investigated. The optimal activity of the immobilized enzymes was around 95°C, the same as the free enzyme. The activity of the immobilized enzyme at 95°C is nearly an order of magnitude higher than the activity at 37°C. We are currently exploring the feasibility of higher enzyme loading and potential effects on solution properties and fiber characteristics.
12:30 PM - Y1.9
Chemical Thermal Stability, Gaseous Catalytic and Sensing Behaviors of ZnO/(La,Sr)CoO3 Composite Nanowire Arrays.
Andy Cai 1 , Paresh Shimpi 1 , Puxian Gao 1
1 , University of connecticut, Storrs, Connecticut, United States
Show AbstractA new class of composite nanowire based nano-catalysts has been synthesized through an integrated two-step fabrication process based on Si flat substrates. The composite nanowire is composed of a de-sulfur ZnO nanowire core and a de-NOx (La,Sr)CoO3 mesoporous nanoshell. A thermal evaporation or wet-chemistry processes were used firstly to grow ZnO nanowire/dendrite skeletons, and then a mesoporous LSCO perovskite nanoparticle coating were deposited on the high surface area of the nano-skeletons using a sol-gel process. ZnO/(La,Sr)CoO3 composite nanowire and nanodendrites have been demonstrated to have excellent chemical/thermal stability as well as photocatalytic and gaseous catalytic properties, as well as gaseous sensing behaviors.
12:45 PM - Y1.10
Characterization of Dispersed Heteropoly Acid on Mesoporous Zeolite using Solid State 31P NMR Spin-Lattice Relaxation.
Jun Liu 1 , Kake Zhu 1 , Jianzhi Hu 1 , Xiaoyan She 1 , Zimin Nie 1 , Yong Wang 1 , Charles H. F. Peden 1 , Ja Hun Kwak 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractDispersion and quantitative characterization of supported catalysts is a grand challenge in catalytic science. In this paper, heteropoly acid H3PW12O40 (HPA) is dispersed on mesoporous zeolite silicalite-1 derived from hydrothermal synthesis using carbon black nanoparticle templates, and the catalytic activity is studied for 1-butene isomerization. The HPAs supported on conventional zeolite and on mesoporous zeolite exhibit very different activities, and thus provide good model systems to investigate the structure dependence of the catalytic properties. The HPA on mesoporous silicalite-1 shows enhanced catalytic activity for 1-butene isomerization, while HPA on conventional silicalite-1 exhibits low activity. To elucidate the structural difference, supported HPA catalysts are characterized using a variety of techniques including 31P magic angle spinning nuclear magnetic resonance (MAS NMR), and are shown to contain a range of species on both mesoporous and conventional zeolites. However, contrary to studies reported in literature, conventional NMR techniques and chemical shifts alone do not provide sufficient information to distinguish the dispersed and aggregated surface species. The dispersed phase and the non-dispersed phase can only be unambiguously and quantitatively characterized using spin-lattice relaxation NMR techniques. The HPA supported on mesoporous zeolite contains a fast relaxation component related to the dispersed catalyst, giving a much higher activity, while the HPA supported on conventional zeolite has essentially only the slow relaxation component with very low activity. The results obtained from this paper demonstrate that the combination of spinning sideband fitting and spin-lattice relaxation techniques can not only provide detailed structural information of the Keggin structure for HPA, but also the degree of dispersion on the support.
Monday PM, November 30, 2009
Room 311 (Hynes)
2:30 PM - **Y2.1
Tailored Mesoporous Silicas: From Confinement Effects to Catalysis.
A. Buchanan 1 , Michelle Kidder 1
1 Chemical Sciences Division, Oak Ridge National Lab, Oak Ridge, Tennessee, United States
Show AbstractOrdered mesoporous silicas continue to find widespread use as supports for diverse applications such as catalysis, separations, and sensors. They provide a versatile platform for these studies because of their high surface area and the ability to control pore size, topology, and surface properties over wide ranges. Furthermore, there is a diverse array of synthetic methodologies for tailoring the pore surface with organic, organometallic, and inorganic functional groups. In this presentation, we will discuss two examples of tailored mesoporous silicas and the resultant impact on chemical reactivity. First, we explore the impact of pore confinement on the thermochemical reactivity of phenethyl phenyl ether (PhCH2CH2OPh, PPE), which is a model of the dominant β-aryl ether linkage present in lignin derived from woody biomass. The influence of PPE surface immobilization, grafting density, silica pore diameter, and presence of a second surface-grafted inert “spacer” molecule on the product selectivity has been examined. We will show that the product selectivity can be substantially altered compared with the inherent gas-phase selectivity. Second, we recently initiated investigation of mesoporous silica supported, heterobimetallic materials for photocatalytic conversion of carbon dioxide. Through surface organometallic chemistry, isolated M-O-M’ species can be generated on mesoporous silicas that form metal to metal charge transfer bands capable of converting CO2 into CO. Initial results from studies of M(IV)-O-Sn(II) [M = Ti, Zr, Hf] on SBA-15 will be presented.
3:00 PM - Y2.2
Key Pore Structure of Zeolite for Selective Production of C3H6 from C2H4.
Toshihide Baba 1 , Yasuyoshi Iwase 1 , To-ru Koyama 1 , Akimitsu Miyaji 1 , Ken Motokura 1
1 , Tokyo Institute of Tehnology, Yokohama Japan
Show AbstractOur group has reported that the conversion of 13C-labeled methane (13CH4) in the presence of ethene (C2H4) proceeds to form 13C-labeled propene (13CC2H6) over Ag+-exchanged zeolites, such as Ag-Y. However, H+-exchanged zeolites, such as H-Y do not yield 13CC2H6, giving only C3H6 as the propene formed. This demonstrates that ethene is converted to propene over Brønsted acid sites.In this work, the conversion of ethylene (C2H4) to propylene (C3H6) was carried out using various zeolites, such as SAPO-34 and CIT-1 to examine the effects of not only physicochemical properties, such as the acid strength of acidic protons, but also various pore structure (pore size and volume) and crystal size of zeolites on the selectivity for C3H6. Zeolites, such as SAPO-34 were packed in a continuous flow reactor. After calcinations of the catalyst, the reaction of C2H4 was carried out using a continuous-flow reactor at atmospheric pressure. Helium served as both a carrier gas and an internal standard for determination of the amount of C2H4 by gas chromatography. The hydrocarbon distributions are expressed on a carbon-number basis, exclusive of the coke remaining in the reactorTo investigate the effect of physicochemical property of catalysts on the C3H6 selectivity, the conversion of C2H4 was carried out using various zeolites at 673 K. The selectivity of C3H6 was plotted against the pore diameter of the catalyst. The C3H6 selectivity over zeolites with 8-members ring was higher than that over zeolites with 10-menbers and 12-members rings. However, among the zeolites with 8-menbers ring, the selectivity for C3H6 strongly depended on the kinds of zeolites, whose pore sizes were almost the same. This means that not only pore size, but also other but also other physicochemical properties, such as pore structure influenced on the C3H6 selectivity. In this presentation, the effect of the pore volume of zeolite together with that of particle size on the selectivity for C3H6 will be shown more in detail. SAPO-34 with the optimum pore volume and pore size can more selectively produce C3H6 than other zeolites. Under optimum reaction conditions, SAPO-34 yielded 55.2% C3H6 with 73.3% selectivity at ethylene conversion of 71.2 %, when the reaction was carried out at 673 K, under 33.3 kPa of C2H4.
3:15 PM - Y2.3
Effect of Nanoparticle Configuration on the Phase and Catalytic Properties of Clay-based Hybrid Materials.
Jung-Kun Lee 1 , You-Hwan Son 1 , Yee Soong 2 , Donald Martello 2 , Minking Chyu 1
1 Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 , National Energy Technology Laboratory, Pittsburgh, Pennsylvania, United States
Show AbstractIn this paper, the effect of nanoparticle configuration on the phase and catalytic properties of montmorillonite-clay based hybrid materials is explored. New iron oxide-clay hybrid particles were synthesized through the ion exchange method. The size and location of α-Fe2O3 nanoparticles depend on the surface properties of Fe polycations. When Fe polycations were intercalated into the interlayer space, embedded iron metal or iron oxide nanoparticles were synthesized. A combination of x-ray diffraction and transmission electron microscopy shows that the location of nanoparticles provides a unique opportunity to control the reducing process of Fe compounds. If the starting nanomaterials are embedded in the interlayer space, the efficiency of the reducing reaction is enhanced due to their high surface area contacting with ambient atmosphere, leading to the easy transition from α-Fe2O3 to Fe3O4 or α-Fe. The magnetization of the hybrid particles is proportional to their content of α-Fe possesses, which is in a good agreement with the fact that the saturated magnetization of the α-Fe is larger than α-Fe2O3 and Fe3O4. Newly developed Fe, Fe2O3, and Fe3O4 nanoparticles embedded in the hybrid particles are exploited to decompose the pollutants and purify water. Their differences in the catalytic efficiency is explained in terms of zero-valent Fe effect and specific surface area.
3:30 PM - Y2.4
Organometallic Synthesis of Nickel Nanoparticles With Different Morphology.
Mar Tristany 1 , Karine Philippot 1 , Bruno Chaudret 1
1 , Laboratoire de Chimie de Coordination du CNRS, Toulouse France
Show AbstractMany efforts have been devoted in the last decades to the preparation of transition-metal nanoparticles. This interest comes from their small size and their particular electronic properties that lead to applications in various fields [1]. The development of synthesis procedures to tune their shape, morphology and size distribution is of high importance because these characteristics have been found to provide subtle control of their chemical and physical properties. For that purpose, the organometallic approach is well-adapted, since it gives rise to well-controlled nanoparticles with tunable size, morphology and surface state [2].Nickel(0) nanoparticles have been studied for their magnetic [3] and catalytic [4] properties. For our part, we are interested in the synthesis of various shape nickel nanoparticles to compare their catalytic activity depending on their exposed surfaces. Nickel nanoparticles were thus prepared by hydrogenation of the organometallic Ni(COD)2 precursor under mild conditions and in presence of various stabilizing agents. The so-obtained nanoparticles were characterized by different techniques (TEM, HREM, SQUID, XRD) and tested in butadiene hydrogenation as supported catalyst.[1] T. Hyeon, Chem Commun., 2003, 927; K. J. Klabunde, in Nanoscale Materials in Chemistry (Ed. K. J. Klabunde), Wiley Intersciences, New York, 2001; M. R. Diehl, J.-Y. Yu, J. R. Heath, G. A. Doyle, S. Sun, C. B. Murray, J. Phys. Chem. B, 2001, 105, 7913; D. L. Leslie-Pelescky, R. D. Rieke, Chem. Mater., 1996, 8, 1770.[2] K. Philippot, B. Chaudret, C. R. Chimie, 2003, 6, 1019-1034; B. Chaudret, C. R. Physique, 2005, 6, 117-131; B. Chaudret, Top. Organomet. Chem., 2005, 16, 233-259; K. Philippot, B. Chaudret, in Comprehensive Organometallic Chemistry III, ed. R. H. Crabtree and M. P. Mingos, Elsevier, 2007, vol. 12, ch. 12.03, pp. 71-99.[3] G.G. Couto, J. J. Klein, W. H. Schreiner, D. H. Mosca, A. J. A. de Oliveira, A. J. G. Zarbin, Journal of Colloid and Interface Science, 2007, 311,461-468; M. R. Knecht, J. C. Garcia-Martinez, R. M. Crooks, Chemistry of Materials, 2007, 19, 1201; Y. T. Jeon, J. Y. Moon, G. H. Lee, J. Park, International Journal of Modern Physics B: Condensed Matter Physics, Statistical Physics, Applied Physics, 2006, 20, 4390-4394.[4] A. Saxena, A. Kumar, S. Mozumdar, J. Mol.Cat. A: Chem., 2007, 269, 35-40; F. Alonso, P. Riente, M. Yus, Synlett, 2007, 12, 1877-1880; R. Xun, T. Xie, Y. Zhao, Nanotechnology, 2007,18, 055602/1-055602/5; M. L. Singla, A. Negi, V. Mahajan, K. C. Singh, D. V. S. Jain, Applied Catalysis, A: General, 2007, 323, 51-57; G.-P. Jin, Y.-F. Ding, P.-P. Zheng, Journal of Power Sources 2007, 166, 80-86.
3:45 PM - Y2.5
CO Oxidation by Pd-doped BaCeO3 Catalysts: The Effect of BaCeO3 Host Interactions with Pd Dopant.
Xiaoying Ouyang 1 , Susannah Scott 1 2
1 Department of Chemistry and Biochemistry, University of California, Santa Barbara, California, United States, 2 Department of Chemical Engineering, University of California, Santa Barbara, California, United States
Show AbstractPerovskite BaCeO3 materials with low levels of substitution of Pd(II) on the Ce site and a corresponding number of oxygen vacancies were prepared by a high-temperature synthesis method. The local structure around Pd(II) was studied by extended X-ray absorption fine structure (EXAFS), and the EXAFS results are consistent with the DFT model which considers a square planar Pd(II) accommodated by tilting of CeO5 square pyramid. Reduction of the Pd-doped BaCeO3 catalysts causes the formation of Pd metallic nanoparticles, confirmed with X-ray diffraction (XRD). Interestingly, the extrusion of Pd dopant induces reconstruction of the perovskite surface, with formation of a Ba-rich surface, confirmed with X-ray photoelectron spectroscopy (XPS). The doping of Pd into BaCeO3 lattice significantly enhanced the catalytic activity for CO oxidation. CO oxidation kinetics, at differential conversions, have been studied on BaCe0.9Pd0.1O2.9 catalysts over a wide pressure and temperature range to investigate the effect of BaCeO3 support interactions with Pd dopant on the catalytic properties. Under CO-lean conditions, the reaction orders for CO and O2 are -1 and 1, respectively. But under CO-rich conditions, the reaction order for O2 is dependent on P(CO). When P(CO)/P(O2) varies from 2 to 30, the reaction order for O2 varies from 1 to 0, which indicates that at high P(CO), the active sites might be poisoned by CO, and O2 from the gas phase has little chance to participate in CO oxidation, thus the adsorbed CO on active sites is actually oxidized by the lattice oxygen from perovskite. Interestingly, it shows two different reaction orders for CO under CO-rich conditions. The reaction order for CO is -0.4 at low P(CO) and 0 at high P(CO), respectively, which again suggests two reaction mechanisms for CO oxidation over Pd-doped BaCeO3, at low P(CO) the reaction between adsorbed CO and adsorbed atomic oxygen is averaged out with the reaction between adsorbed CO and lattice oxygen from perovskite, however at high P(CO) only the reaction that lattice oxygen participated is prominent. Steady state isotopic transient kinetic analysis (SSITKA) by using 18O2 for CO oxidation confirmed the coexistence of the two reaction mechanisms mentioned above, and the reaction between adsorbed CO with lattice oxygen from perovskite can be promoted by higher temperature.
4:30 PM - Y2.6
Effect of Particle Size and Shape on NH3 Decomposition on Ru.
Ayman Karim 1 3 , Vinay Prasad 1 4 , Giannis Mpourmpakis 1 , Anatoly Frenkel 2 , William Lonergan 1 , Jingguang Chen 1 , Dionisios Vlachos 1
1 Chemical Engineering Department, University of Delaware, Newark, Delaware, United States, 3 Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, Washington, United States, 4 Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 Department of Physics, Yeshiva University, New York, New York, United States
Show AbstractNH3 synthesis and decomposition on Ru have been reported to be structure sensitive reactions [1-3]. The active sites for ammonia synthesis have been reported by Jacobsen et al. to be B5-type step sites [1]. Several groups have hypothesized the optimal Ru particle size for the highest concentration of B5 sites to be in the range of 1.8-2.5 nm [1-3]. If all types of step sites are considered, Gavnholt and Schiøtz reported the optimal Ru particle size to be around 3 nm [4]. However, to our knowledge, there has not been a study where the Ru particle size has been varied over a large range. In addition, different Ru particle shapes have not been investigated.In this work, we synthesized Ru/γ-Al2O3 catalysts with different average Ru particle size, ranging from 0.8 nm to 7.1 nm. We show that catalyst pretreatment has a strong effect on Ru average particle size as well as particle shape. The average Ru particle size was measured using electron microscopy and the Ru dispersion was measured using CO chemisorption. In order to estimate the Ru particle shape, images of the spent catalysts obtained by high resolution transmission electron microscopy (HRTEM) were combined with the first four shell coordination numbers obtained from Extended X-ray Absorption Fine Structure (EXAFS). We show that for small particles, a unique solution for a single shape can be obtained by combining the results from electron microscopy, CO chemisorption and EXAFS. We show that the TOF of NH3 decomposition increases by almost 2 orders of magnitude on Ru particle sizes ranging from 0.8-7.1 nm.[1]Jacobsen C.J.H., Dahl S., Hansen P.L., Tornqvist E., Jansen L., Topsoe H., Prip D.V., Moenshaug P.B., Chorkendorff I., J Mol Catal A: Chem 163, 19 (2000). [2]Raróg-Pilecka W., Miskiewicz E., Szmigiel D., Kowalczyk Z., J. Catal., 231, 11 (2005) [3]Zheng W., Zhang J., Xu H., Li W., Catal. Lett. 119, 311 (2007)[4]Ganvnholt P. and Schiøtz J., Phys. Rev. B 77, 035404 (2008)
4:45 PM - Y2.7
Nanoporous Ni-Pt Based Materials for the Oxygen Reduction Reaction.
Joshua Snyder 2 1 , Jonah Erlebacher 1 2
2 Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 1 Materials Science, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractElectrochemical dissolution of Ni from Ni-Pt based bulk alloys are shown to result in a highly porous material, with pore sizes ~3 nm in diameter, and specific surface areas ~50 m2/g. We have assessed these materials for the oxygen reduction reaction, toward which they are highly active, a result correlated to the ~30% residual Ni content and Pt skin. The half-wave for oxygen reduction can be pushed greater than 0.97 V vs. RHE. We interpret this result as primarily due to roughness effects within the model of Wang, Zhang, and Adzic (2007). In contrast to typical porous electrodes, however, there appears to be little mass transport limitations within the porous layer. Materials synthesis strategies employing the use of ternary or quaternary based precursor alloys to improve the oxygen reduction kinetic current will be discussed.
5:00 PM - Y2.8
Highly Dispersed and Uniform Pt Nanoparticles over Spherical-Al2O3 by Atomic Layer Deposition: Synthesis and Characterization.
Jeffrey Miller 1 , Hao Feng 1 , Jeffrey Elam 2 , Jeffrey Miller 1 , Christopher Marshall 1 , Fabio Ribeiro 3 , Eric Stach 4 , Seung Min Kim 4
1 Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Energy Systems Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Chemical Engineering, Purdue University, West Lafayette, Indiana, United States, 4 Materials Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractAtomic Layer Deposition (ALD) was used as an alternative method to conventional impregnation for the depositing of Pt over spherical-Al2O3 support. The main advantage of using ALD was that the Pt particles were uniformly dispersed over the surface of the support with very narrow particle size distribution. In-situ X-ray absorption fine-structure (XAFS) was used to determine the mechanism of the Pt nanoparticle formation during ALD and to monitor Pt particle size and oxidation state during catalyst evaluation. Transmission electron micrograph (TEM) was utilized to measure the size and distribution of Pt particles. Pt/sp-Al2O3 catalysts were synthesized in an in-house design ALD system. The support, sp-Al2O3 (NanoDur®, Alfa Aesar) has spherical shape with diameter around 40-50 nm and the surface area of approximately 30-40 m2/g. The reactor setup for Pt ALD over powder support consisted of a quartz tube reactor in an enclosed furnace, an organometallic precursor bubbler and a vacuum pump. Methylcyclopentadienyl trimethyl platinum (IV) (MeCpPtMe3) (Strem Chemicals) was loaded into the precursor bubbler in a glove box, then transferred and connected to the main reactor set up. Prior to Pt ALD, the sp-Al2O3 was degassed at 150°C under vacuum with a flow of He. Pt ALD has 4 main steps in each ALD cycle: 1) Pt dosing at 100 or 300°C; 2) Purging with He; 3) Removal of organic ligand with 4% H2/He or air at 300°C; 4) Purging with He. Similar ALD system was used for the in situ XAFS ALD experiments to determine the Pt ALD mechanism. X-ray absorption near edge structure (XANES) at the Pt L3 edge and Extended X-ray absorption fine structure (EXAFS) were recorded at each ALD steps until no changes in the spectra were observed. The measurements were conducted at the insertion-device beamline of the Materials Research Collaborative Access Team (MR-CAT) at the Advanced Photon Source, Argonne National Laboratory.During Pt ALD, Pt loading increased linearly with the number of Pt cycles and the particle size also increased. In general, the Pt ALD mechanism consisted of MeCpPtMe3 adsorbed on the hydroxyl sites, then most of the precursor decomposed as the support was heated up to 300°C in He. The remainder of the organic ligand was decomposed when exposed to air or H2. When air was applied as treatment gas, the Pt particles were oxidized to PtO. With H2, Pt particles maintained as metallic Pt. Pt particle size from ALD depended on the support type and treatment gas. Air provided larger Pt particle size than when H2 was used for 1 cycle Pt ALD over sp-Al2O3.
5:15 PM - Y2.9
Water Adsorption and Dissociation on Reduced Anatase TiO2 (101) Surfaces.
Ulrich Aschauer 1 , Hongzhi Cheng 1 , Yunbin He 2 3 , Shao-Chun Li 2 , Ulrike Diebold 2 , Annabella Selloni 1
1 Departement of Chemistry, Princeton University, Princeton, New Jersey, United States, 2 Department of Physics, Tulane University, New Orleans, Louisiana, United States, 3 Faculty of Materials Science & Engineering, Hubei University, Wuhan, Hubei, China
Show AbstractTiO2 is a material with a wide application field, most notably in photocatalytic processes such as hydrogen production and solar energy conversion. Since most applications of TiO2 involve an aqueous environment, the interaction of its surfaces with water is of great interest. The Anatase phase, although known to be more reactive, has been significantly less studied than rutile. This makes the investigation of this phase and in particular it’s most abundant (101) surface a topic of great interest.Recently our groups have established the predominance of subsurface defects, particularly oxygen vacancies, on reduced anatase (101) (He et al., PRL, 102(10), 106105, (2009) and Cheng and Selloni, PRB, 79(9), 092101, (2009)). Using the same combined approach based on Scanning Tunneling Microscopy (STM) measurements, Density Functional Theory (DFT) calculations and First Principles Molecular Dynamics (FPMD) simulations, in this work we investigate the reactivity of the reduced anatase (101) surface toward water adsorption. Our DFT calculations show a strong site dependence of the reactivity with respect to the subsurface vacancy position, which is also seen in STM experiments. Water adsorption in proximity of the subsurface vacancy is favored, and dissociative adsorption is only ~ 0.1 eV less favorable than adsorption in molecular form at this site, whereas the difference is ~ 0.4 eV at regular sites. Moreover calculations using the nudged elastic band method show that also the water dissociation barrier depends on the position of the adsorption site, being particularly low, ~ 0.2 eV, in proximity of the subsurface vacancy. In fact, water dissociation events at this site are observed in FPMD simulations. These results indicate that subsurface defects mediate water adsorption and dissociation on reduced anatase (101) surfaces. The newly gained understanding on the role of subsurface vacancies in water adsorption and dissociation on the anatase (101) surface can be useful both for the interpretation of surface science experiments and to advance our understanding of photocatalytic processes.
5:30 PM - Y2.10
Plasmon Assisted Control of Heterogeneous Catalysis.
James Adleman 1 , David Boyd 1 , David Goodwin 1 , Demetri Psaltis 2 1
1 Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, United States, 2 School of Engineering, EPFL, Lausanne Switzerland
Show AbstractWe introduce a new method for studying in situ many types of heterogenous catalysis.The method makes use of the plasmon resonance present in nanoscale metal catalysts themselves to provide the necessary heat of reaction whenilluminated with a low power laser. We demonstrate our approach by reforming a flowing, liquid mixture of ethanol and water in a microfluidic channelembedded with a self-assembled array of gold nanoparticles, which serve as the catalysts. The heat generated in the gold nanoparticles allows vapor to be generated and reactions to take place locally, and the products of the reaction, CO2, CO, CH4, and H2, are consistent with steam reforming of ethanol. The approach, which we refer to Plasmon-Assisted Catalysis, is general and can be used with a variety of processes. A feature of the localized heating is that it allows the reactor system to be at room temperature. We will discuss our results as well as the advantages, challenges, and potential applications of the technique.
5:45 PM - Y2.11
Novel Green Routes For Synthesizing Zeolites.
Feng-Shou Xiao 1
1 , Jilin Univ, Changchun China
Show AbstractAluminosilicate zeolites have been widely applied in the petroleum catalysis and refining industry, and most of industrial applications require these zeolites with a low cost and friendly to the environment. However, modern synthesis technologies are normally used by organic templates for their synthesis, which leads to the increase of zeolite cost and the formation of environmentally unfriendly gas formed by the removal of organic templates calcined at high temperature. To save the energy and reduce the synthesis cost, the best way is to synthesize zeolites in the absence of organic templates. This work shows novel green routes for organotemplate-free synthesis of ZSM-34, ECR-1, and Beta zeolites. ZSM-34 is an intergrowth of offretite and erionite zeolite, ECR-1 is an intimate twin of the mordenite-like sheets between layers of mazzite-like cages, and Beta zeolite has three-dimensional 12-ring pores. It is believable that the successful synthesis of these zeolites in the absence of organic templates would be very important for their industrial applications.
Y3: Poster Session
Session Chairs
Tuesday AM, December 01, 2009
Exhibit Hall D (Hynes)
9:00 PM - Y3.1
IR and XRD Amorphous Synthesis Residue Showing Zeolitic Micropores.
Anthony Chiang 1 , Sewn-Yi Fun 1 , Jan-Sen Wu 1 , Tseng-Chang Tsai 2
1 Chem& Mater. Eng., National Central University, Chung-Li Taiwan, 2 Applied Chemistry Dept., National University of Kaohsiung, Kaohsiung Taiwan
Show AbstractDue to its three-dimensional interconnected channels, with 12-membered elliptical openings having mean diameters of 0.64 X 0.76 nm, Beta zeolite has been a good candidate as catalyst for isomerization or hydroisomerization (with metal) of C6-C8 n-alkanes, as well as an effective adsorbent for the separation of hexane isomers. The synthesis of beta zeolite is however not straightforward, and often suffers from a low crystalline yield. This is particularly true when one follows the clear sol approach to synthesis colloidal beta zeolite for catalyst or adsorbent with smaller crystal size ad thus less diffusion resistance. In this study, nano-size (<80 nm) BEA zeolite was synthesis by the hydrothermal reaction of clear TEOS/ATIP/TEAOH/H2O synthesis sol at 90oC for extended period. By introducing a vacuum evaporation step before the hydrothermal reaction, which brought the silica concentration to 30 wt%, we were able to reduce the crystallization time from 10 days to 5 days. The crystalline product was separated by high speed centrifuge to calculate the zeolite yield. The particle size distributions, XRD and IR spectra of the amorphous solids in the supernatant and the crystalline sediments were also followed. The maximum yield achieved was 50 wt%, independent of the evaporation step. However, to our surprise, the XRD and IR amorphous solids in the supernatant turned out to be uniform nanoparticles which, after calcination, showed similar micropore volume as that of the centrifuged BEA nanocrystals. The hexane isomer TPD measurements further indicated that both the crystalline and the amorphous products were more selective toward the smaller hexane molecule. Therefore, at least in terms of the adsorption capacity and the selective for hexane isomers there is no need to remove the amorphous part of the product before use as adsorbent or catalyst.
9:00 PM - Y3.11
Design of Nanocomposite Cermets for Hydrogen Production and SOFC Anodes.
Natalia Mezentseva 1 , Vladislav Sadykov 1 2 , Galina Alikina 1 , Rimma Bunina 1 , Vladimir Pelipenko 1 , Oleg Bobrenok 3 , Alevtina Smirnova 4 , Julian Ross 5 , Oleg Smorygo 6
1 , Boreskov Institute of Catalysis, Novosibirsk Russian Federation, 2 , Novosibirsk State University, Novosibirsk Russian Federation, 3 , Institute of Thermal Physics, Novosibirsk Russian Federation, 4 Connecticut Global Fuel Cell Center, University of Connecticut, Storrs, Connecticut, United States, 5 Centre of Environmental Research, University of Limerick, Limerick Ireland, 6 , Powder Metallurgy Institute, Minsk Belarus
Show AbstractDesign of materials able to efficiently perform steam reforming of CH4 or biofuels without coke deposition in the 500-600 C range is important but demanding problem for hydrogen energy including internal reforming of fuels on SOFC anodes. A promising approach consists in synthesis of nanocomposites comprised of components able to efficiently activate C-H and C-C bonds in the fuel molecules (Ni, precious metals) and oxide components providing activation of water molecules and transfer of hydroxyls and/or hydroxocarbonate/oxygen species to the metal particles where they interact with C-H-O species producing syngas. Nanocomposite cermets comprised of Ni particles (10-60 wt.%) embedded into complex oxide matrix (Y- or Sc-stabilized zirconia combined with doped Ce-Zr oxides or perovskites) and promoted by Pt or Ru were synthesized via Pechini and (co)impregnation routes. Samples were characterized by BET, XRD, TEM with EDX, H2 and CH4 TPR. The catalytic properties of nanocomposite materials were studied in the SR of CH4, ethanol and acetone at short contact times. Applied preparation procedures result in pronounced interaction between nanocrystalline active components including decoration of NiO/Ni particles by oxidic fragments, epitaxial intergrowth between particles of different phases, incorporation of Ni, Pt and Ru cations into perovskite or fluorite particles, redistribution of elements between phases directly revealed by EDX and reflected in variation of lattice spacings and particle sizes. TPR spectra show strong effect of this interaction on oxides reactivity, oxygen mobility and ability of surface sites in reduced nanocomposites to dissociate CH4 yielding H2 while carbon is stored as surface/bulk hydroxocarbonates without surface blocking by coke deposits.In SR of all fuels in stoichiometric feeds, developed nanocomposite cermets possess a high and stable activity even at 500- 600 C, coking being completely suppressed. For easily activated biofuels, promotion by Pt or Ru does not improve performance determined mainly by the oxygen mobility in doped ceria-zirconia or perovskite oxides and accessible Ni surface decorated by oxidic species, the highest activity being achieved for systems with Pr-La-Ce-Zr-O additive. In CH4 SR, Pt and Ru as co-promoters help to activate CH4, thus providing a high activity at temperatures ~ 600 C. Performance of best compositions supported as porous strongly adhering layers on Ni/YSZ anode cermets or crofer/fechraloy nonporous/porous monolithic substrates was demonstrated to be also high and stable for all types of fuels (even glycerol and sunflower oil) ensuring reformate composition close to equilibrium. Any cracking or detachment of layers after reaction was absent, making these systems promising for efficient in-cell SR of methane or biofuels. This work is supported by NATO SFP 980878, Integration Project 57 of SB RAS and Project 57 of Presidium RAS.
9:00 PM - Y3.12
Tuning Near-surface Oxygen Concentration in Nanoscale Ceria Films Through Photo-excitation.
Masaru Tsuchiya 1 , Shriram Ramanathan 1
1 Harvard School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractCeria has been widely used in various catalytic applications, including the three-way catalysis for the automobile pollution control, water-gas shift reaction and steam reforming of hydrocarbons. For all of these applications, near surface oxygen defects play crucial role in determining the catalytic activities. Despite these experimental evidences on the role of oxygen defects on activities of ceria surfaces, few studies are available for the quantitative relationship between oxygen defects and catalytic activities at present. In this presentation, we will overview an unique approach to tailor near surface oxygen defect properties in nanoscale ceria thin films utilizing ultraviolet (UV) photon irradiation. Nanoscale films are a good model system to investigate near surface oxygen defects properties due to its large surface-to-volume ratio.Ceria thin films of nearly identical thickness (~ 65 nm) were grown on sapphire c-plane substrates by molecular beam epitaxy (MBE) and electron beam (e-beam) evaporation. The microstructure of these two films were distinctly different; MBE grown film was highly textured in [111] direction, while e-beam grown film was randomly oriented with nanocrystalline (~ 30 nm) grains. Grain growth kinetics in nanocrystalline e-beam grown film was self-limiting and the out-of-plane orientation was found to be substrate and annealing ambient dependent. From electrical conductivity relaxation measurements, oxygen surface exchange kinetics in nanocrystalline ceria was found to be faster than that in highly textured ceria. The relaxation time to the change in P(O2) from 1.07 x 10−12 to 5.43 x 10−10 Pa at 1148 K was 0.65 s for highly textured films, while it was only 0.13 s under identical conditions.The extent of oxygen nonstoichiometry on properties was systematically studied by utilizing UV irradiation. The proximity of photon energy to the bond energy of oxygen molecule creates activated oxygen species, thereby oxygen kinetics are enhanced under UV. This process is very effective even at near room temperature; thereby we can use this as a method to manipulate anion point defects. Ceria films were grown by room temperature oxidation of dc-sputtered Ce metal thin films with and without UV irradiation. The valence state of Ce at ceria surface grown by natural oxidation was a mixture of Ce3+ and Ce4+, while UV grown ceria had no distinct Ce3+ peaks. Interestingly, UV grown ceria were preferably oriented along [111] direction even at room temperature, while naturally oxidized ceria had random orientation. These differences can lead to interesting changes in catalytic activity as well.Detailed quantitative and physical analysis on the relationship between structure, oxygen defects and oxidation/reduction kinetics will be given in this presentation.
9:00 PM - Y3.13
Plasmonic-based Detection of Harsh Environment Emissions Gases by Thin Film Nanocomposites.
Phillip Rogers 1 , Nicholas Joy 1 , Michael Carpenter 1
1 College of Nanoscale Science and Engineering, University at Albany, State University of New York, Albany, New York, United States
Show AbstractThe development of novel harsh environment compatible chemical sensing technologies is of critical need for optimal control of future zero and low emission power production as current sensor technologies cannot withstand these environments. Gold nanoparticle embedded yttria-stabilized zirconia (Au-YSZ) and titanium oxide (Au-TiO2) nanocomposite films have been deposited on optically transparent sapphire substrates. The Au nanoparticle localized surface plasmon resonance (LSPR) band was monitored as concentrations of oxygen, hydrogen, and nitrogen dioxide in nitrogen, were varied and flowed over nanocomposite films at elevated temperatures. Titration experiments were performed and will be discussed in terms of reactions occurring between exposure gases, Au nanoparticles and embedded matrix, which result in charge transfer to and from the Au nanoparticles upon concentration changes in gas exposure environment. We monitored electrochemical charge transfer caused by catalytic reactions occurring between the nanocomposite and exposure environment by monitoring the optical properties of the nanocomposite thin films, specifically the peak position and dampening of the LSPR band. We have clarified that the shifts observed in the LSPR band peak position for these nanocomposites agrees with free electron theory, and have developed a model which relates the observed broadening of the LSPR band to inelastic scattering of the surface plasmons by diffusing oxygen ions. Arrays of Au-YSZ and Au-TiO2 nanocomposites have been deposited in an attempt to increase the selectivity of these nanomaterials for future use in harsh environment sensing applications. The further development of deposition techniques to more finely tune nanocomposite particle size and matrix doping to enhance selectivity of sensing arrays is also underway.
9:00 PM - Y3.14
Morphology-dependent Optical Absorption and Conduction Properties of PEC Photocatalysts for H2 Production: A Case Study.
Muhammad Huda 1 , John Turner 1
1 , National Renewable Energy Lab, Golden, Colorado, United States
Show AbstractEfficient photoelectrochemical H2 production by solar irradiation depends not only on the photo-catalyst’s band gap and its band-edge positions, but also on the detailed electronic nature of the bands, such as localization or delocalization of the band edges and their orbital characters. These determine its carrier transport properties, reactivity, light absorption strength etc. and significantly impact its efficiency as a photoconverter. The localization or delocalization of band edges may arise either due to the orbital nature of the bands or the structural morphology of the materials. A recent experimental report on a photo-catalyst based on s/p orbitals showed very poor performance for H2 production despite the delocalized nature of the s/p bands as compared to the d-bands of transition metal oxides. It is then important to examine whether this poor performance is inherent to these materials or rather arises from some experimental limitations. A theoretical analysis by first-principle methods is well suited to shed light on this question.
9:00 PM - Y3.17
Reduction on Aluminum Nanoparticles: A Simple Method to Synthesize Porous Metallic Nanostructures.
Qingzhou Cui 1 , Jacqueline Pelealuw 2 , Julie Chen 2 , Zhiyong Gu 1
1 Chemical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts, United States, 2 Mechanical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractIn the present study, we explore the synthesis of metal nanostructures from a new template material - aluminum (Al) nanoparticles by the reduction method. The standard reduction potential of Al3+/Al is -1.66 V [versus standard hydrogen electrode (SHE)], which can reduce most other metal ions in solution. Due to the confinement effect of the aluminum nanoparticles, the reduction reaction takes place on each individual aluminum nanoparticle through a mechanism known as galvanic replacement reaction. The new template material improves our ability to fabricate new discrete nanostructures such as core-shell nanoparticles in a scalable, batch process. In this paper, we demonstrate that we can extend the galvanic replacement reaction to synthesize porous magnetic metallic nanostructures including Ni, Co, Fe, etc. Synthesis of other metallic nanostructures including Cu, Pd, and Pt is also demonstrated from the reduction on the Al nanoparticles. These nanostructures have been characterized by SEM, TEM, EDAX and XRD. The effectiveness of these novel porous materials for applications such as catalysts and nanoscale heating materials (nano-heaters) is under investigation.
9:00 PM - Y3.18
Theoretical Analysis of the CO Oxidation Processes on Neutral and Single Ionized Au18 Clusters.
Jorge Castro 1 2 , Jorge Soto 2 , Bertha Molina 2 , Alipio Calles 2
1 Dep. Física, CINVESTAV del IPN, Mexico City, Del. Gustavo A.Madero, Mexico, 2 Dep. Física, Fac. Ciencias, UNAM, Mexico,D.F. Mexico
Show AbstractExperiments on the reactivity of CO for Au nanoclusters have shown a local maximum in the adsorption of the first molecule for Au18 and its cation, whereas O2 adsorption has been observed in Au18-. In this work we present a theoretical analysis of the preferential sites for the adsorption of the CO and O2 molecules on neutral and single ionized Au18 clusters with C2v symmetry, which has been shown both theoretical and experimentally, to be the most stable isomer of the Au18 cluster. We present the results of the calculation for the binding energies of CO for non-equivalent sites and compare with the experimental values. We also present the analysis of the reaction path and barrier energies for the CO oxidation around the most favourable O2 adsorption site. The study is based on a DFT-GGA calculation with the PW91 functional.
9:00 PM - Y3.19
Atomic-level Control of Oxygen Non-stoichiometry at Oxide Surfaces Through Electric Fields: Atomistic Simulation Studies.
Subramanian Sankaranarayanan 1 , Shriram Ramanathan 1
1 Materials Science, Harvard University, Cambridge, Massachusetts, United States
Show AbstractSynthesis of ultra-thin oxide films with controlled functional properties is of tremendous technological importance. These applications include but are not limited to templates for model catalysts and passivation layers to protect against corrosion. Oxide non-stoichiometry is an important factor which significantly affects the functional properties of metal oxides and hence their applicability. Here, we report on the ability to athermally control oxygen non-stoichiometry in ultra-thin zirconium and aluminum oxides through local electric field perturbations. Using two representative examples of Al(100) and Zr(0001) oxidation, we report on the ability to modify the structure and composition (Metal/Oxygen) of ultra-thin oxides grown on metal surfaces at room temperature by utilizing externally applied electric fields. Molecular dynamic simulations employing dynamic charge transfer between metal atoms is used to model the oxidation process in the presence of external electric fields. Precise understanding of the microscopic processes involved in electric field assisted oxidation of metal substrates is provided by the atomistic models employing dynamic charge transfer between atoms. We show for the first time that electric field-assisted synthesis can be used to overcome the activation energy barrier for ionic migration leading to significantly enhanced oxidation kinetics, enabling us to control the oxide composition at atomic length scales. For example, we find that activation energy barrier for Zr(0001) oxidation decreased from 1.13 eV with no field to 0.08eV for an applied field of 10 MV/cm. The calculated structural and dynamical correlation functions indicate that externally applied electric field (~ 10^7 V/cm) drives the surface chemisorbed oxygen to the vacancy sites in the oxide interior leading to dramatic density and stoichiometry improvements of the grown ultra-thin oxide film. Oxide stoichiometry (O/Zr ratio) for natural oxidation with no field was 1.42 indicative of a sub-stoichiometric and oxygen deficient oxide which increased to near stoichiometric value of 1.86 for 10 MV/cm field assisted oxidation. Similarly, the application of 15 MV/cm electric field in case of Al(100) oxidation increased oxygen stoichiometry from 1.27 to 1.40, respectively. Our simulations thus demonstrate a pathway to athermally control oxygen concentration in near-surface regions that is of great importance to contemporary problems utilizing ultra-thin oxides ranging from catalysis to energy technologies.
9:00 PM - Y3.2
Study of Catalytic Activity of Magnetic Nanoparticles by Chemiluminescent Probe Reaction.
Galyna Krylova 1 , Elena Shevchenko 1
1 Center for Nanoscale Materials, Argonne National laboratory, Lemont, Illinois, United States
Show AbstractMagnetic nanoparticles (MNP) are extensively studied because of the great promise for ultrahigh-density magnetic recording media, biomedicine, catalysis, gas sensors, etc. Surface chemistry of MNPs can be optimized by control over states of surface atoms and tailored molecules that significantly affect their activity and specificity. Iron-based MNPs are widely used as MRI, hypothermia, drug delivery agents. However, there is a fear to use cobalt-based nanoparticles associated with potential harm to the cells due to reactivity of cobalt despite better magnetic properties. Co(II) is known to lead to the formation of free OH radicals and replace Zn and Mg active sites in co-enzymes. An advanced catalytic performance was shown for transition metal/platinum magnetic alloy with carefully removed surface atoms of transition metals. Thus it is important to monitor the surface states of the initial transition metal-based MNPs and their surface transformation during processes (catalysis, surface functionalization, etc) and storage in the real conditions of their applications. In this contribution we suggest to probe transition metal atoms with highly sensitive chemiluminescent (CL) reaction of luminol and hydrogen peroxide and compare our observation with XPS data. The cations Fe(II) and Co(II) interact with hydrogen peroxide producing hydroxyl radicals which further initiate luminol oxidation accompanied by the blue light emission. We have found that magnetic CoPt3 and Co nanoparticles of different sizes can catalyze the decomposition of luminol while iron based nanoparticles have not resulted in detectable CL response. These data indicate significant number of Co(II) at the surface of cobalt-based MNPs and lack of Fe(II) at the surface of iron-based MNPs (FexOy, PtxFey). No CL has been detected for CoPt3/Au dumbbells as well, that provides evidence of surface Co(II) atoms participation in reduction of Au(III) during the growth of dumbbells. Also we have observed slow removal of Co from the surface of MNPs in aqueous media that finally results in complete transfer of surface cobalt into the solution; however, it is likely that “bulk” cobalt atoms stay intact. We will report the comparative study of magnetic properties of initial MNPs and MNPs with cobalt-deficient surface layer. Moreover Au and Pt constituents of MNP have been found to scavenge OH radicals leading to the decrease of CL intensity. The obtained results contribute to understanding of the principles of MNPs’ design and surface modification for rendering them desirable properties e.g. biocompatibility, increased catalytic activity and selectivity without substantial loss of their magnetic response.
9:00 PM - Y3.21
Synthesis and Characterization of Photocatalysts for Overall Water Splitting under Visible-Light Irradiation.
Limin Wang 1 , Wei Kang 2 , Peichuan Shen 3 , Mark Hybertsen 2 , Alexander Orlov 3 , Peter Khalifah 4 1
1 Chemistry, Brookhaven National Laboratory, Upton, New York, United States, 2 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States, 3 Materials Science and Engineering, Stony Brook University, Stony Brook, New York, United States, 4 Chemistry, Stony Brook University, Stony Brook, New York, United States
Show AbstractThe development of visible-light-responsive semiconductors for water splitting is a necessary step towards efficiently and economically producing renewable H2 fuel using solar energy. Recent work on visible light absorbing perovskite and pyrochlore-related oxides synthesized by powder and single crystal methods will be discussed, including optical, electrochemical, and theoretical studies. The resulting picture of the energy levels in these materials, including evidence for raised valence band energies, will be presented in the context of the detailed structural characterization of these phases.
9:00 PM - Y3.22
PVA-assisted Hydrothermal Preparation of Nano-size Bi25FeO40 and Their Photocatalytic Activity.
Cheng Jinrong 1 , Li Jianmin 1
1 , Shanghai university, Shanghai China
Show AbstractBi25FeO40 have attracted increasing attention because of its various properties ,such as photorefractivity, optical activity, and photoconductivity. A PVA-assisted hydrothermal synthesis route was utilized to fabricated single-phase Bi25FeO40 crystallites. X-ray diffraction (XRD) results indicated that sillenite Bi25FeO40 have been synthesized at the temperature of 200 degrees centigrade using the KOH concentration of 4M. The band gap of Bi25FeO40, as determined by using UV-vis diffuse reflectance spectroscopy (UV-DRS),was found to be 2.2eV (564nm).The photocatalytic activity was evaluated by the degradation of methyl orange under UV-visible irradiation and was found to be higher than that of the well-known TiO2-xNx photocatalyst,suggesting that Bi25FeO40 might be a potential material for photocatalytic decomposition of organic contaminants.The possible formation mechanism of Bi25FeO40 is also discussed.
9:00 PM - Y3.23
Dye-sensitized Solar Cell Using a TiO2 Nanocrystalline Film Electrode Prepared by Solution Combustion Synthesis.
Shyan-Lung Chung 1 , Ching-Mei Wang 1
1 , National Cheng Kung University, Tainan Taiwan
Show AbstractA solution combustion synthesis method was developed to prepare the TiO2 nanocrystalline film electrode for fabrication of dye-sensitized solar cells (DSSC). DSSC based on nanoporous TiO2 electrodes are currently attracting widespread and intense academic and industrial interest for the conversion of sunlight into electricity. We have recently launched in our laboratory a research program aiming to study the key materials and technologies for developing low cost and highly efficient DSSCs. In this presentation, we will report a study on the fabrication of DSSC with nanoporous TiO2 electrodes which were prepared using TiO2 nanoparticles with different morphologies and different crystalline structures. These TiO2 particles were synthesized by a solution combustion synthesis method by using metal nitrates as the oxidizer and using urea or glycine as the fuel. Titanium n-butoxide was used as the precursor. It was first hydrolyzed to obtain titanyl hydroxide [TiO(OH)2], which was then converted to titanyl nitrate [TiO(NO3)2] by reacting with nitric acid. The TiO(NO3)2 in aqueous solution was added with a fuel (i.e., urea or glycine) and was then heated to initiate the combustion synthesis reaction. The properties of the products thus synthesized, e.g., morphology, specific surface area, porosity, crystalline phase and band gap, were found to be strongly affected by the experimental conditions such as fuel type, fuel to oxidizer ratio, and combustion temperature. TiO2 nanoparticles with different sizes, morphologies and different crystalline structures can be obtained and controlled by changing the experimental parameters. These TiO2 with different properties were used to prepare the film electrodes and DSSCs were fabricated. The photoelectric conversion efficiency was found to depend strongly on the properties of the TiO2. Up to date, the highest efficiency obtained was 5.7% with Voc=677mV, Isc=19.15mAcm-2 and F.F.=0.44. Further investigation is being undertaken to study the effect of the properties of TiO2 on the photoelectric conversion efficiency.
9:00 PM - Y3.24
The Effects of Doping Sites of Vanadium Ions on the Physicochemical and Photocatalytic Properties of TiO2.
Sue-min Chang 1 , Wei-szu Liu 1
1 , National Chiao Tung University, Hshinchu Taiwan
Show AbstractBulk and surface incorporation of TiO2 with vanadium ions have been done using sol-gel and surface sol-gel method. The effect of doping sites on the physicochemical properties including crystalline transformation, bandgaps, charge trapping and interfacial charge transfer was investigated. Moreover, the photocatalytic activities of bulk and surface doped TiO2 were characterized. The UV-vis spectra of the bulk doped TiO2 shows an additional absorption band at 250~286 nm when the V/Ti ratio was below 1.7×10-3, indicating the appearance of extra energy levels in the conduction bands because of V5+ ions. Significant red-shift of the absorption edge of TiO2 to 500 nm, corresponding to 2.5 eV, was observed as the V/Ti increased to 1.27×10-2. In which V4+ became dominant in the bulk lattice. In contrast to the reduced states, V5+ ions were the primary one at the surface site. Pure TiO2 was anatase mainly and had an average crystal size of 8.4 nm. Bulk doped vanadium ions decreased the anatase crystal size to 7.1 nm, while surface doped ions had little effects on the microstructures. Grazing angle XRD results show that the surface doped TiO2 was coated with a thin V2O5 shell, ¬while the V2O5 crystals were dispersed in the surface layer of bulk doped TiO2. The SIMS and XPS data of the bulk doped samples also indicated that the surface V/Ti ratios were 2 times higher than the total ones. These findings reveal the low solubility of V5+ in the TiO2 lattice. Pure TiO2 exhibited rate constant of 6.3×10-2 1/min for the photocatalytic degradation of Rhodamine B(RhB). Bulk doping decreased the activity to 6-fold when the V/Ti ratio increased to 1.2 ×10-2. In contrast, surface doping enhanced the rate constants to 1.4-fold at the same V/Ti ratio. Substantial recombination centers at V4+ sites lead to detrimental effects on the low photocatalytic activity of bulk doped samples. However, surface V2O5 shell promotes electrons diffusion to surface and further facilities charges transfer to reactants, thereby greatly improving the degradation efficiency.
9:00 PM - Y3.28
Photocatalytic Degradation of Pharmaceuticals and Mechanical Filtration by TiO2 Nanowire Membranes.
Anming Hu 1 , Shine Zhang 2 , K. Oakes 2 , N. Zhou 1 , M. Servos 2
1 Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Ontario, Canada, 2 Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
Show AbstractTiO2 nanowire membranes have the potential for the removal of emerging contaminants in wastewater. Recently, we have successfully fabricated gram-level TiO2 nanowires through an environmentally friendly hydrothermal growth process. After annealing at 600oC for 2 hours under ambient atmosphere, X-ray diffraction patterns show these nanowires are in the anatase mineral form of TiO2. Experiments demonstrate that these TiO2 nanowires are typically up to 100 µm in size, and can be processed into different devices such as 2-dimensional membranes or 3-dimensional cups through spin-coating and casting. UV-Vis diffuse reflection spectra show that the optical energy gap of obtained TiO2 membranes is 3.35 eV. Permeability of TiO2 nanowire membranes was characterized using a polycrystalline diamond suspension solution containing particles with a mean diameter of 250 nm. The concentration of diamond particles was determined by UV-Vis absorption spectra against calibration curves. The results illustrate filtration of diamond solutions by either two-layer paper filter (Whatman™# 1001042) or TiO2 membranes. A spectrum of pure H2O is also displayed for comparison. An absorption band centered at 265 nm (4.67 eV) corresponds to the sp3-bonded diamond phase. It is evident that 250 nm diamond particles can easily pass through the filter paper, whose filtering efficiency did not change with the addition of a second filtering step (data not shown). In contrast, TiO2 membranes effectively removed 95% of the diamond nanoparticles utilizing a 0.5 mm thick membrane).Photocatalytic degradation was evaluated as follows: a complex solution of 22 pharmaceuticals (including monensin, trimethoprim, fluoxetine, triclocarban, atorvastatin, among others) at concentrations of approximately 100 µg/L was used as the initial test solution. The persistence of analytes in treatments with and without TiO2 membranes, and in the presence and absence of 100 W UV irradiation, were evaluated to elucidate both compound degradation by TiO2 nanowires, and impacts of surface absorption. The concentration of the pharmaceutical analytes was sampled as a function of time in all treatments using solid phase extraction, with final analyte concentrations determined by HPLC–tandem mass spectrometry. The results illustrate the degradation of the antibiotic trimethoprim following exposure to TiO2 nanowires/UV irradiation. Stable trimethoprim concentrations over time in treatments lacking both UV irradiation and TiO2 nanowires strongly suggests photocatalytic degradation is responsible for the trimethoprim removal. Similar degradation responses were observed for fluoxetine, monensin, norfluoxetine, 17α-ethinylestradiol, and triclocarban.
9:00 PM - Y3.29
Microfibrous Entrapped Catalysts for Low Temperature CO Oxidation.
Shirish Punde 1 , Bruce Tatarchuk 1
1 Chemical Engineering, Auburn University, Auburn, Alabama, United States
Show AbstractLow temperature CO oxidation is characterized by slow reaction kinetics and CO self-poisoning of the catalyst, which compete with each other. A platinum catalyst with ceria as a promoter supported on a high surface area silica support has been developed. The catalyst has a significant activity for CO oxidation even in the presence of moisture. The catalyst showed a significant increase in activity with decreasing particle size (η<0.95, even at 100µm), indicating a clear transport limitation.In case of larger catalyst particles the diffusional resistances affect the reaction kinetics, leading to greater rates of CO self-poisoning causing deactivation of the catalysts. However, conventional packed bed of smaller particles poses problems such as high pressure drop, packing issues, bed channeling, flow maldistributions, and dead zones in the reactor bed, which result in poor inter-phase heat and mass transfer rates. Most of these problems are related to poor packaging of smaller particles, strongly suggesting the need for immobilization of small particles. A new class of micro-structured materials consisting of sorbents/catalysts entrapped in metal, ceramic, or polymer microfibers (MFES/MFEC) has been developed at Auburn University. These materials immobilize the small particles by sinter-locking them in fiber mesh. The immobilization of particles results in better heterogeneous contacting efficiency. Additional studies have shown that the high voidages and structural uniformity of the MFES lowered the flow maldistributions, eliminated the peaking flows between particles, and helped achieve better radial dispersion. Thus MFEC/MFES improved inter-phase transport rates. The Pt-CeO2/SiO2 catalyst entrapped in metal microfibers demonstrated a significant improvement in CO conversion compared to a conventional packed bed configuration while maintaining a lower pressure drop. Further catalyst entrapment in metal microfibers minimized cold spots in the reactor bed due to better intra-phase heat transfer rate. Higher effective thermal conductivity of MFEC improved the activity of the catalyst, which was particularly visible at high CO concentration wherein the CO inhibition kinetics takes over. For example, MFEC with 1/3rd of catalyst loading as that of packed bed of same particle size, outperformed packed bed configuration.The catalysts were prepared by incipient wet impregnation. Surface characterization of catalysts was carried out using CO, H2, O2 chemisorption, O2 – H2 titration, N2 physisorption, powder XRD, and was correlated with catalytic activity. This microfibrous entrapped catalyst demonstrated a great potential for low temperature CO oxidation. These MFEC can be used in air purification, emergency escape products, and as a cathode air filter for PEM fuel cells.
9:00 PM - Y3.3
Novel Electrode Coating based on Metal-cyclam Complexes and Polymeric Nanofiber Assembly.
Yingjun Liu 1 , Xiaohu Xie 1
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractA novel electrode coating with artificial enzyme immoblized in nanofiber is developed. The artificial enzyme is designed with metal-cyclam complexes as redox active center, which can catalyze superoxide reduction reaction. Porous nanofiber membrane is intoduced on the surface of electrode to enhance electron transfer and molecules exchange. The perfomances of the biosensor are characterized with surface enhanced raman spectroscopy, mass spectroscopy, X-ray diffraction, cyclic voltammetry. This novel electrode coating has great potential to applied for water splitting and hydrogen production.
9:00 PM - Y3.30
Defect Engineering of the Electrochemical Characteristics of Carbon Nanotubes for Catalytic Applications.
Mark Hoefer 1 , Prabhakar Bandaru 1
1 Materials Science, Mechanical Engineering department, University of California, San Diego, La Jolla, California, United States
Show AbstractWe consider the electrochemical behavior of carbon nanotubes (CNTs) containing both intrinsic and extrinsically introduced defects, through Cyclic Voltammetry and Raman Spectroscopy. Bamboo and hollow multi-walled carbon nanotube morphologies provide examples of the former while the controlled addition of argon ions was used for studying extrinsic defects. We show that the electrocatalytic response of the hollow type CNTs can be tailored more significantly compared to bamboo type CNTs, which have innately high reactive site densities and are less amenable to modification. The work also has implications in the design of nanotube and nanowire based chemical sensors and energy storage.
9:00 PM - Y3.31
Investigation on the Contradictory Gas Sensing Behaviors of Semiconducting ZnO and Zn2SnO4 Single Crystalline Nanowires Arrays.
Andy Cai 1 , Puxian Gao 1
1 , University of connecticut, Storrs, Connecticut, United States
Show AbstractBoth ZnO and Zn2SnO4 nanowire arrays were found sensitive to ethanol at ~150 oC in both close and open enviroments upon ~150 ppm ethanol pulses, resulting in a sensitivity of 10 and 25, respectively. Positive and negative responses were observed in these two sensors, respectively. The increased conductivity in ZnO nanowire sensor is attributed to the direct sensing of ethanol molecules as a result of surface donation of electrons from ethanol reduction. The reduced conductivity in Zn2SnO4 sensor might be due to the catalytic activation of ambient oxygen detection triggered by the ethanol pulses associated with residual Ag2O nanoparticles decorated around the nanowire surfaces and electrodes-nanowire film interfaces. In order to verify the theory, Ar plasma treatment was utilized in Zn2SnO4 sensor and a reversed sensing trend was achieved, leading to resistance drop upon ethanol pulses. The semiconducting oxide nanowires decorated with Ag2O nanoparticles presented here could bring up new nanosensor design through a unique reversible catalytic oxidation/redox chemical detection mechanism. They may find potential applications in vehicle and petrochemical flammable and toxic gas detection.
9:00 PM - Y3.32
In situ X-ray Characterization of Oxygen Reduction in La0.6Sr0.4Co0.2Fe0.8O3-δ at Elevated Temperature and Variable Oxygen Partial Pressure.
Tim Fister 1 , Dillon Fong 1 , Jeffrey Eastman 1 , Paul Salvador 2 , Balasubramaniam Kavaipatti 2 3 , Paul Fuoss 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 3 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractWith its desirable combination of catalytic, transport, and thermal properties, the mixed conducting perovskite La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) is becoming a standard cathode material in solid oxide fuel cells. Here, we focus on epitaxial thin films as model cathodes to isolate surface and bulk reactions. Using in situ synchrotron x-ray scattering and spectroscopy, we focus on two possible rate-limiting steps in the performance of LSCF: oxygen reduction at the surface and ionic transport within the bulk. At 700°C, fractional-order in-plane diffraction peaks indicate an atomic surface reconstruction in (001)-oriented LSCF thin films. We examine this feature as a function of oxygen partial pressure, temperature, and crystal orientation. Following surface reduction, we examine the nature of oxygen transport through LSCF via vacancies in the perovskite lattice. Comparing the cobalt and iron x-ray absorption spectra, we find that the minority cobalt sites are preferentially reduced with increasing temperature. We also find decreasing coordination number near the cobalt atoms, confirming that oxygen vacancies are largely localized near these sites.This work was provided by the U.S. Department of Energy (DOE), Basic Energy Sciences, under contract DE-AC02-06CH11357 and through the DOE Solid State Energy Conversion Alliance (SECA) program
9:00 PM - Y3.34
Effects of Zn Doping and High Energy Ball Milling on the Photocatalytic Properties of TiO2.
Paula Algarin 1 , Li Chennan 1 , Nikolai Kislov 1 , Sesha Srinivasan 1 , Ayala Phani 2 , Elias Stefanakos 1 , Yogi Goswami 1
1 Clean Energy Research Center, University of South Florida, Tampa, Florida, United States, 2 , Nano-RAM Technologies, Bangalore India
Show AbstractThis paper explores the effects of Zn doped TiO2, prepared by the sol-gel method, on its photocatalytic activity to decompose organics and the characterization of the doped samples. Preliminary examination revealed a relatively low photocatalytic efficiency of the samples. The objective is to modify/improve its properties by high energy ball milling which is expected to generate accumulations of defects, particle size reduction and an increase in the active surface area. The characterization of doped and mechanochemical treated materials has been analyzed by optical diffuse reflectance measurements and optical absorption calculations using the Kubelka-Munk approach. The phase structure and particle size of the materials were determined using X-ray diffraction (XRD). The BET surface area of the samples is obtained using an Autosorb instrument. The photocatalytic decomposition properties of Methyl Orange in an aqueous solution were systematically studied using built in-house tubular reactor with capability of operation using UV and/or fluorescent light.
9:00 PM - Y3.35
Enhancement of TiO2 Organic Degradation Ability Under Visible Light by N Doping.
Li Chennan 1 , Nikolai Kislov 1 , Sesha Srinivasan 1 , Elias Stefanakos 1 , Yogi Goswami 1
1 Clean Energy Research Center, University of South Florida, Tampa, Florida, United States
Show AbstractThis paper investigated a relative inexpensive way to lower band gap of commercial TiO2 by doping it with nitrogen and enhanced its photoactivity under visible light. It accomplishes substitutional nitrogen doping of the catalyst using a gas phase impregnation method which anhydrous ammonia was used as a nitrogen source and doping amount was further optimized. Experiments showed that photocatalytic effect increases with increasing nitrogen concentration. This continues until a threshold concentration (625oC, 2-3 hours) is exceeded at which point the photocatalytic efficiency decreases. Further, catalysts were characterized and doping mechanism was discussed. The photocatalytic decomposition properties of Methyl Orange in an aqueous solution were systematically studied and modeled using built in-house tubular reactor with capability of operation using UV and/or fluorescent light. The positive results showed the application potential of N-doping TiO2 in municipal water/wastewater treatment process.
9:00 PM - Y3.36
Fabricating Nanocomposite Catalysts through Interfacial Fusion of Metallic Nanoparticles.
Yong-Jae Choi 1 , Chi-Kai Chiu 1 , Tsan-Yao Chen 1 , Tzy-Jiun Luo 1
1 Materials Science and Engineering, NC State University, Raleigh, North Carolina, United States
Show AbstractFusion of metallic nanoparticles at both surfaces of silica colloids and nanoporous bulk materials has been utilized as an effective method to integrate inorganic and organic components into nanocomposite materials. When performed on substrates that have been modified with aprotic functional groups, silica colloids decorated with metallic nanoparticles adhere to the substrates and self-assemble into nanocomposite film with its thickness being the function of the time. This is made possible through ethylenediamine functional groups on the silica colloids. In contrast, without metal-bound functional groups, fusion of metallic nanoparticles can be induced at the interface of nanoporous silica composite without affecting the silica structure if polymer is utilized as the mobile phase. Formation, mobilization, and fusion of metallic nanoparticles within the polymer phase can be simultaneously induced at 160 C, during which reactions contribute to the physical change of the materials from transparent to silver metallic color. These two fusion methods are suitable to create functional structures through either soft-lithography or contact-imprint methods that exhibit electrochemical property. Furthermore, two fusion methods when combined with titanium oxide allow us to fabricate nanocomposite catalysts that are suitable for solar cell and fuel cell electrodes.
9:00 PM - Y3.37
Degradation of Semiconductor Photoelectrodes in Aqueous Environments from Ab-initio Molecular Dynamics.
Brandon Wood 1 , Tadashi Ogitsu 1 , Eric Schwegler 1
1 , LLNL, Livermore, California, United States
Show AbstractAmong currently known approaches for hydrogen production, catalytic splitting of water molecules using semiconductor-based photoelectrochemical (PEC) devices has garnered particular interest, with reasonably high efficiencies already demonstrated in laboratory conditions. Unfortunately, these materials often evidence extremely facile surface corrosion, severely limiting theirpractical use in real-world devices. Currently, a clear understanding of this corrosion process at the water-semiconductor interface and its damaging effecton catalytic activity is lacking. Although certain theoretical efforts have attempted to address this issue, these studies have generally focused on zero-temperature gas-phase molecular adsorption, forgoing a realistic model of the liquid-solid interface. Accordingly, we have performed extensive ab-initio molecular dynamics simulations to probe the structure, chemistry, and dynamicsof the water-electrode interface for model semiconductor systems in a realistic aqueous environment. Our work has focused on InP and GaAs, which, although structurally and functionally similar, exhibit substantial differences in terms of stability in an aqueous environment and in surface reactivity. These calculations are able to provide a unique in-depth understanding of surface structure and transport. As such, they promise to provide a crucial first step towards understanding the complex interplay between the atomistic processes involved in hydrogen evolution and PEC corrosion.
9:00 PM - Y3.38
Optical Bandgap Widening of P-Type Cu2O Flms by Nitrogen Doping.
Yoshitaka Nakano 1 , Shu Saeki 1 , Takeshi Morikawa 1
1 , TOYOTA Central R&D Laboratories, Inc., Nagakute, Aichi, Japan
Show AbstractCu2O is a direct-gap semiconductor with a bandgap energy of ~2.1eV and spontaneously shows p-type conductivity. From the viewpoint of solar energy conversion, Cu2O can be one of good p-type candidates for semiconductor-based photocatalysis and/or photoelectrolysis [1]. Particularly for the application of solar hydrogen production from water, the energy band structure of p-type Cu2O needs to be modified to position the conduction and valence band edges on optimal levels where the conduction band must be above 0V vs. normal hydrogen electrode (NHE) to produce H2 with high efficiency, and the valence band must be below +1.2V vs. NHE to produce O2. Thus, the modification of the Cu2O band structure will count for facilitating photoredox processes after the electron-hole formation upon absorption of a visible-light photon.In this study, we have investigated the effect of N doping into Cu2O films deposited by reactive magnetron sputtering at 400°C using a metallic Cu target in a mixture of Ar, O2, and N2. In order to control N-doping concentration in N-doped Cu2O (Cu2O:N) films, the flow rate of N2 was varied between 0 and 20sccm, with retaining that of Ar+1%O2 mixture gas at 50sccm. All the Cu2O:N samples were confirmed to be polycrystallized and to show p-type conductivity with hole carrier concentrations in the 1016cm-3 range as well as the Cu2O reference sample by XRD and room-temperature Hall-effect measurements, respectively.By XPS analyses, the N-doping concentrations are determined to be 2.3, 2.7, and 2.9% for the Cu2O:N samples prepared under the N2 flow rate of 1.5, 2.5, and 10sccm, respectively. Also, the doping limit of N into Cu2O is found to be ~3%. From optical absorption measurements, the optical bandgap energy Eg of the Cu2O:N films is seen to increase from ~2.1 to ~2.5eV with increasing N2 doping concentration up to 3%. Additionally, photoelectron spectroscopy in air measurements show an increase in the valence and conduction band shifts with the N doping. These experimental results demonstrate possible optical bandgap widening of p-type N-doped Cu2O films, which phenomenon with repeatability is definitely associated with significant structural changes induced by the N doping, as suggested from XRD measurements. Thus, the N doping into Cu2O in this study is considered to artfully generate oxygen vacancies rather than the acceptor doping, which is in reasonable agreement with our previous study of N-doped TiO2 films [2].The p-type Cu2O:N films equipped with various conduction and valence band edges are of great worth as one of promising p-type semiconductors for semiconductor-based photocatalysis and/or photoelectrolysis. These experimental findings in this study and their further detailed investigations are likely to provide important information on the materials design.[1] M. Hara et al., Chem. Commun. 3, 357 (1998).[2] Y. Nakano et al., Appl. Phys. Lett. 86, 132104 (2005).
9:00 PM - Y3.39
Assembly and Interfacial Effects in Hybrid Nanostructures of Zinc Oxide and Gold.
Daisuke Ito 1 2 , James Hutchison 2
1 Environment & Energy Development Dept., Core Device Development Group, Sony Corporation, Atsugi, Kanagawa, Japan, 2 Department of Chemistry and Materials Science Institute, University of Oregon, Eugene, Oregon, United States
Show AbstractZinc oxide (ZnO) is a promising candidate for electric, opt-electric and catalytic applications because of its wide direct band gap of 3.37 eV and large exciton binding energy of 60 meV. In particular, hierarchical and aligned ZnO nanostructures have potential in a wide variety of applications besides nano-optelectrics. To utilize these novel ZnO nanostructures in high-performance materials and devices, fabrication techniques are needed that are highly reproducible, scale to large areas, are low cost, and produce little waste. Previously, we reported a greener method of to control ZnO nanowire growth using chemically anchored Au nanoparticle catalysts. Chemical anchoring can also be used to add novel functions to the finished nanomaterials by ligand interconnections. We demonstrate fabrication methods and characteristics of ligand interconnected ZnO/gold nanostructures, such as nanowires and nano-network arrays that are interfaced with Au nanoparticles. Interconnection between ZnO and Au nanoparticle by 2-mercaptoethylphosphonic acid enhances the sensitivity of the photoconduction to carbon dioxide or methanol gas, providing 100 times higher sensitivity than bare ZnO nanostructures. Because the interconnection is conducted in a Au nanoparticle solution and nanoparticles anchor on only ZnO surface, this technique minimizes the amount of gold waste. We also demonstrate a couple of ZnO/metal and ZnO/metaloxide nanostructures interconnected with organic or inorganic self-assembled monolayer ligands. These ligand interconnection techniques might lead to realize exotic nano-hybrid devices.
9:00 PM - Y3.4
Fabrication and Performance of Catalyst-based Solid-state Sensors for Room Temperature Hydrogen Leak Detection.
Ryan Givens 1 , Claudiu Muntele 1 , Stefon Lewis 1 , Kudus Ogbara 1 , Daryush Ila 1
1 , Alabama A&M University, Normal, Alabama, United States
Show AbstractSilicon carbide based non-linear electronics devices (MOSFET, metal-semiconductor, or p-n junctions) are promising candidates for hydrogen detection schemes if used in conjunction with a platinum group catalyst. For the past decade, the emphasis was mostly on high temperature applications in the automotive (for hydrogen-fueled engines) and in the aerospace industry (for jet engines), but now the focus is broadening to include auxiliary systems such as storage tanks, fuel lines, fuel production systems, all operating in a wide range of temperatures, all the way down to cryogenic levels. Here we are presenting an innovative approach to designing a capacitive configuration sensor solution to address challenges associated with using catalysts as active agents in ultra-sensitive capacitive hydrogen detection schemes at ambiental temperatures. We used e-beam deposition for preparing our samples, and current vs. voltage electrical measurements to monitor the devices’ response to hydrogen. Raman spectroscopy, scanning electron microscopy, and atomic force microscopy were used for investigating the surface morphology of the device and process metrology. Performance results as a function of hydrogen ppm concentration in air and inert environments will be presenting at the meeting.
9:00 PM - Y3.40
Environmental Friendly and Highly Regioselective Oxybromination in Aqueous System by Using SBA-15 Supported Sulfated Zirconia Catalyst.
Chen Ai-Jan 1 , Mou Chung-Yuan 1 2 , Chen Xiao-Rong 3
1 Chemistry, National Taiwan University , Taipei Taiwan, 2 Center of Condensed Matter Science, National Taiwan University, Taipei Taiwan, 3 College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing China
Show AbstractBrominated aromatic compounds have been used widely in synthetic organic chemistry in the manufacture of many bulk and fine chemicals. Particularly, they are versatile synthetic starting materials in carbon-carbon bond formation reactions. In contrast to direct bromination by toxic elemental bromine or HBr used as a bromine source, we developed a safe system for oxybromination by using hydrogen peroxide and ammonium bromide in aqueous phase under mild temperature and near neutral pH condition over sulfated zirconia (SZ). The ready availability of the catalyst and nearly neutral aqueous solution condition employed are the salutary features of this approach. Especially, hydrogen peroxide is a desirable oxidant due to its miscibility with water and ease of handling.Bromination of aromatics with electron-withdrawing group took place readily, and bromoproducts were produced as the products in moderate to excellent yields. A good to excellent para-selectivity was observed. The SZ/SBA-15 catalyst may be re-used several times without substantial loss of activity.We also studied the catalytic activity on bromination with SZ which were supported on mesoporous SBA-15 silica or mesoporous SZ. Silica supported SZ (SZ/SBA-15) shows much improved catalytic ability for bromination then self-supported SZ (m-SZ). Furthermore, we found that catalytic activity of SZ was decreased at higher calcination temperature. The good catalytic performance of the SZ/SBA-15 materials was attributed to high degree of dispersion of sulfate groups to give sulfated silica-zirconia of (1) very good redox property and (2) high strength and high density of acid sites.
9:00 PM - Y3.42
Preparation of FeTiO3/TiO2 Heterojunction and its Photocatalytic Activity Under Visible Light Irradiation.
Song Yi Han 1 , In Gyoung Yu 1 , Kyeong Ha Kim 1 , Wan In Lee 1
1 , Inha University, Incheon Korea (the Republic of)
Show AbstractTiO2 shows very low photocatalytic activity in the visible range even though it shows an excellent efficiency under UV light irradiation. In order to overcome such drawback, we develop a new system that can absorb the light in visible range so that the electron is excited to CB of sensitizer and the hole is created in the VB of TiO2 which can be used for oxidation reaction. The FeTiO3 shows a profound absorption over the entire visible range, and its VB position is close to that of TiO2. Thus it is deduced that the unusually high photocatalytic efficiency of the FeTiO3/TiO2 composite is caused by the hole transfer between VB of FeTiO3 and TiO2. FeTiO3 nanodisc was prepared by hydrothermal reaction. Its size was ~300nm with a shape of hexagonal disc. The heterojunction of FeTiO3/TiO2 was prepared by combining the Degussa P25 and FeTiO3 nanodisc by an organic linker. Then it was applied to the degradation of 2-propanol in gas phase and 4-chlorophenol in aqueous solution under visible light irradiation. The photocatalysis results revealed that the FeTiO3/TiO2 composites exhibited much higher activity than the pure TiO2 and FeTiO3 in the photocatalytic oxidation reactions. Furthermore, it shows a good photochemical stability in the repeated photocatalytic applications.
9:00 PM - Y3.43
Electrochemical Properties of Doped (La0.68Sr0.32)1-δMnO3 Thin Film Fuel Cell Electrodes.
Di Chen 1 , WooChul Jung 1 , Harry Tuller 1
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractProgress in achieving improved solid oxide fuel cell (SOFC) performance, particularly at intermediate temperatures (<800oC), is largely constrained by inadequate cathode catalytic activity. While the current material of choice, (La,Sr)MnO3 (LSM), provides many desired properties, such as, high electronic conductivity, chemical and thermal compatibility with the YSZ electrolyte, and low cost, its performance deteriorates rapidly as the operating temperature is reduced. In this study, the impact on cathode performance of the systematic substitution of foreign ions on both the A and B sublattice of the perovskite LSM structure as well as control of the A/B ratio (i.e. δ) are examined. In order to better understand the source of the change in performance, well defined and reproducible dense thin film LSM cathodes with controlled texture were prepared by pulsed layer deposition onto single crystal YSZ, and their electrochemical and catalytic properties examined by complex impedance spectroscopy. The observed trends are discussed in relation to the defect and transport properties of LSM.
9:00 PM - Y3.44
High-resolution in-situ Environmental TEM Observation of Dynamic Behavior of Au/CeO2 Catalysts in CO/Air.
Tetsuya Uchiyama 1 , Hideto Yoshida 1 , Tomoki Akita 2 , Masanori Kohyama 2 , Hideo Kohno 1 , Masatake Haruta 3 , Seiji Takeda 1
1 Graduate School of Science, Osaka University, Osaka Japan, 2 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Osaka Japan, 3 Faculty of Urban Environmental Sciences, Tokyo Metropolitan University, Tokyo Japan
Show AbstractGold in bulk is chemically inert and has often been regarded to be poorly active as a catalyst. However, when gold is deposited as a hemispherical nanoparicles on a selected metal oxide, it shows high catalytic activity in various reactions [1]. For example, gold nanoparticles supported on CeO2 show high catalytic activity in CO oxidation and water-gas-shift reaction. Catalytic activity of gold nanoparticles depends on not only nanoparticle size but also support materials. There is a controversy over the reaction mechanism. Three models about the reaction mechanism are proposed. (1) Perimeter interface between gold nanoparticle and the support is the active site [2]. (2) Gold cations induce reactions [3]. (3) Non metallic nature of gold nanoparticles relate with the reaction mechanism [4]. In order to clarify the reaction mechanism, high-resolution in-situ observation of gold catalyst in reaction conditions is indispensable. We observed Au/CeO2 catalysts in various gases using an environmental transmission electron microscope (ETEM [5]) that enables us to obtain high-resolution in-situ images in a reactive gas of up to several thousand Pa.Au/CeO2 catalysts (gold content: 5wt%) were prepared by a deposition precipitation method. CO/Air consists of CO 1%, O2 21% and N2 78%. This sample shows catalytic activity in CO oxidation at RT. We observed structural changes of gold nanoparticles depending on gas species. Detailed observations will be presented.[1] M. Haruta, Catalysis Today 36 (1997) 153[2] M. Haruta, CATTECH 6 (2002) 102[3] Q. Fu, H. Saltsburg, M. Flytzani-Stephanopoulos, Science 301 (2003) 935[4] M. Valden, X. Lai, and D.W. Goodman, Science 281 (1998) 1647[5] H. Yoshida and S. Takeda, Phys. Rev. B 72 (2005) 195428.
9:00 PM - Y3.45
Immobilization of Polyoxometallate Anions in the Interlayer Space of Surface-Modified Layered Metal Oxide.
Tae Woo Kim 1 , In Young Kim 1 , Seong-Ju Hwang 1
1 Department of Chemistry and Nano sciences, Center for Intelligent Nano-Bio Materials (CINBM), Ewha Womans University, Seoul Korea (the Republic of)
Show AbstractWe have developed a new methodology of surface modification for the intercalative hybridization of anionic polyoxometallate species with negatively charged metal oxide nanosheets. To begin, we have expanded the interlayer distance of protonic layered titanate by the intercalation of octylamine. And then, 3-aminopropyltriethoxysilane (APS) was anchored onto the interlayer surface of layered titanate by condensation reaction between hydroxyl groups on the surface of the titanate sheet and ethoxy groups of APS. The surface modification of layered titanate by APS-anchoring was confirmed by 29Si magic angle spinning-nuclear magnetic resonance (29Si MAS-NMR) and FT-IR spectroscopy underscoring the formation of Si-O-Ti bond. According to zeta potential measurement, the surface-modified layered titanate shows positive surface charge at pH < 6, which contrasts with the pristine layered titanate having zero surface charge at the same pH region. In this way, we were successful in intercalating anionic polyoxometallate (i.e. decavanadate) into the surface-modified layered titanate. The crystal structure and chemical bonding nature of the decavanadate-intercalated titanates were systematically investigated together with their catalytic activity.
9:00 PM - Y3.46
Preparation and Characterization of TiO2 Nanorods for the High Performance Photo-catalyst.
Hyeong Jin Yun 1 , Hyunjoo Lee 2 , Ji Bong Joo 1 , Wooyoung Kim 1 , Nam Dong Kim 1 , Jongheop Yi 1
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractThe development of high performance photo-catalyst is an important subject for the effective conversion of solar energy to electric energy. For this purpose, TiO2 has been attracted much interest as a photo-catalyst for a variety of promising applications. Photocatalytic reaction is conducted via the charge transfer between photo-catalysts and reactants under light illumination. Thus, the amount of e–/h+ on the photo-catalyst surface is a key factor in determining the photocatalytic reaction rate. In this work, we report on the influence of aspect ratio of TiO2 nanorods on the e–/h+ recombination probability and subsequently photo-catalytic performances. In order to varify the shape effect of TiO2 nanoparticles, a variety of shape-controlled TiO2 nanoparticles were prepared and characterized, such as spheres, ellipsoidal rods with a low aspect ratio (low AR), and high aspect ratio (high AR). Experimental results showed that the high aspect ratio of TiO2 nanoparticles increased the charge-transfer rate through interfacial region of the electrolyte due to the reduction of probability of e–/h+ recombination. In addition, the lifetime of e- and h+ on the active sites under the light illumination increased with the increase in the aspect ratio of TiO2 nanoparticles. Thus, the use of high-AR ellipsoidal TiO2 nanoparticles as photocatalysts resulted in enhanced current density and, consequently, an increase in the photocatalytic performances.
9:00 PM - Y3.47
Preparation and Characterization of Nitrogen-doped Mesoporous Carbon Materials using Nitrogen-contained Carbon Precursors.
Wooyoung Kim 1 , Mi Yeong Kang 1 , Ji Bong Joo 1 , Nam Dong Kim 1 , Hyeong Jin Yun 1 , Jongheop Yi 1
1 School of chemical and biological engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractOrdered mesoporous carbon materials (OMCs) have drawn much attention in practical and fundamental research due to their high surface area and regular framework with narrow pore size distribution. Thus, OMCs have been considerd as a promising material for the use of an adsorbent, catalyst support and electrode materials. In addition to the structural properties, the surface chemistry of OMCs via functionalization is an important factor for the tagetted and tailor-made applications. The general way to functionalize carbon surface is a post-treatment which uses acidic solution for the attaching the functional group onto the surface. However, post-treatment may often cause not only the destruction of pore structure but non-uniformly functionlized surface. Another way for the surface functionalization of OMCs is to employ a ploymer with a functionality as a carbon precursor. It should be noted that most mesoporous carbons prepared using such a polymer are rod-type, such as CMK-3. On the other hand, the tube-type, such as CMK-5, is known to have somewhat different pore structure from rod-type one. It is well known that it is difficult to functionalize the surface of tube-type carbons. More importantly, a post-process, such as the use of acidic solution, is not desirable for the functionalization of the surface due to the weak pore structure of the tube-type carbons. In this work, we developed one-step method for the preparation of the nitrogen-functionalized carbons with tube-type using a nitrogen-containing polymer (poly-quinoline) as a carbon precursor. Based on the analyses of SAXS and nitrogen adsorption-desorption isotherm, it was observed that the fabricated carbon materials had high surface area and similar pore structure to the CMK-5 that was typically prepared using furfuryl alcohol as carbon precursor. The elemental analysis and XPS results clearly showed that the surface of prepared OMC was successfully functionalized with nitrogen.
9:00 PM - Y3.48
TiO2 Nanotubes Doped with Nitrogen for Visible-light Photocatalyst.
Se Im Kim 1 , Sung Wook Lee 1 , Jun Mo Yang 2 , BeeLyong Yang 1
1 Dept of Information nano materials, Kumoh National Institute of Technology, Gumi, Geongbuk, 730-701 Korea (the Republic of), 2 National Nanofab Center, Measurement & Analysis Team, KAIST, Eoeun-dong, Yuseong-gu, Daejeon 305-806 Korea (the Republic of)
Show AbstractWe report photocatalytic properties of nitrogen-doped TiO2 (TiO2-XNX) nanotube arrays to address issues of improving the efficiency of water-splitting under visible-light irradiation. TiO2 nanotube arrays with ~2um length and ~180nm diameter were grown by anodizing Ti foils using electrolytes based on DMSO (dimethyl sulfoxide) and acid solutions. The amorphous samples after the anodization were annealed to crystallize at 550°C in oxygen ambient for 4hr. Then to dope nitrogen into TiO2 nanotube arrays, they were annealed in NH3 ambient as a function of different times and temperatures. Results of nanostructural analysis by FE-SEM, XRD and TEM for these samples show that the TiO2 nanaotubes fabricated by the DMSO based-electrolyte consist of 2-3 grains, compared to the samples using the acid-based electrolytes with complete polycrystalline structures. We believe that the reason why the larger grains of the TiO2 nanotubes by the DMSO electrolytes show superior photocatalytic properties is mainly due to less recombination sites of electron-hole pairs created by light excitation, resulting from less grain boundaries. The GC and band gap measurement, and photo-conversion efficiency of the N-doped TiO2 nanotubes for visible light water-splitting will be also discussed.
9:00 PM - Y3.49
Visible-light Water-splitting Performance of TiO2 Nanotube-arrays using Co-catalysts of WO3, Cr2O3, and BiVO4.
Su Min Son 1 , Ji Hoon Whang 1 , Jun Mo Yang 2 , BeeLyong Yang 1
1 Dept of Information nano materials, Kumoh National Institute of Technology, Gumi, Geongbuk Korea (the Republic of), 2 National Nanofab Center, KAIST, Measurement & Analysis Team, Yuseong-gu, Daejeon 305-806 Korea (the Republic of)
Show AbstractWe report photocatalytic properties for composites of TiO2 nanotube/metal oxides(WO3 and BiVO4) to address issues of improving the efficiency of water-splitting under visible-light irradiation. TiO2 nanotube arrays with ~2um length and ~180nm diameter were grown by anodizing Ti foils using electrolytes based on DMSO (dimethyl sulfoxide). The amorphous samples after the anodization were annealed to crystallize at 550οC in oxygen ambient for 4hr. Then after dipping TiO2 nanotube arrays into metal oxide liquid solutions such as V-acetylacetonate, Cr(NO3)3H2O, H2WO4 and Bi(NO3)2H2O, they were annealed in O2 ambient as a function of different times and temperatures. Results of nano-structural analysis by FE-SEM, XRD and TEM for these samples show that metal oxides nano-particles of ~10nm diameter formed stably on the surface of TiO2 nanotubes. Effects of the co-catalysts for TiO2 nanotubes were investigated by photo-current and GC measurements under visible light and the results will be presented in terms of photo-conversion efficiency for water-splitting.
9:00 PM - Y3.5
One-pot Direct Hydrothermal Approach to the Design and Fabrication of Photoactive Materials.
Dimitra Vernardou 1 2 3 , Emmanouil Spanakis 2 3 4 , George Kenanakis 1 2 4 , Emmanouil Koudoumas 1 5 , Nikos Katsarakis 1 2 4
1 Center of Materials Technology and Laser, School of Applied Technology, Technological Educational Institute of Crete, Heraklion Greece, 2 Science Department, School of Applied Technology, Technological Educational Institute of Crete, 710 04 Heraklion, Crete, Greece., Technological Educational Institute of Crete, Heraklion Greece, 3 Department of Materials Science and Technology, University of Crete, Heraklion Greece, 4 , Institute of Electronic Structure and Laser, Foundation for Research & Technology-Hellas, Heraklion Greece, 5 Electrical Engineering Department, Technological Educational Institute of Crete, Heraklion Greece
Show AbstractThe term ‘photoactive materials’ stands for the key elements in a wide range of multi-functional applications, ranging from absorbing or emitting layers in photovoltaic and other optoelectronic devices, and comprises the new classes of metamaterials along with photocatalytic metal oxides. This paper will address photocatalysis through vanadium oxide, tungsten oxide and zinc oxide and the strategies underpinning their growth using a ‘solution processing method’. Among the transition metal oxides, V2O5 (vanadium (V) oxide) (with the band gap energy of 2.80 eV [1]) is a subject of intensive study because its photocatalytic property makes it a promising candidate for the degradation of organic pollutants such as hydrocarbons (not only alkenes but also alkanes). This has a great advantage since degradation of propene over illuminated TiO2 (titanium dioxide) gives carbon dioxide even at low level of conversion of propene [2]. Tungsten Oxide (WO3) has drawn much attention because of its high efficiency in photocatalytic degradation of organic compounds, including a large fraction of environmental toxins. Furthermore, it can be an alternative to TiO2 as it also absorbs blue light [3]. Finally, ZnO (zinc oxide) is a semiconductor that has a similar band gap to TiO2, however it is not thoroughly investigated as a catalysis agent. The greatest advantage of ZnO is that it has higher absorption coefficient than TiO2. One-pot direct hydrothermal growth of these oxides has received a lot of interest because it is a simple, cost-effective and environmental friendly route to prepare (amorphous or crystalline) thin films at low temperature (≤ 95 oC) and short reaction time over a wide range of substrates. We find that coherent photoactive V2O5, WO3 and ZnO layers can be deposited using hydrothermal growth at 95 oC. The photoinduced catalytic activity in degrading stearic acid under UV illumination, is of the order of 57 % for V2O5, 43 % for ZnO and 40% for WO3. We may thus conclude that V2O5 is a most promising alternative to hydrothermally grown TiO2 for photocatalytic applications. References[1] Y. Xu, M.A. Schoonen, Am. Mineral. 85 (2000) 543.[2] J.-M. Herrmann, J. Disdier, M.-N. Mozzanega, P. Pichat, J. Catal. 60 (1979) 369.[3] G. Waldner, A. Brüger, N.S. Gaikward, M. Neumann-Spallart, Chemosphere 67 (2007) 779.[4] N. Daneshvar, S. Aber, M.S. Seyed Dorraji, A.R. Khataee, M.H. Rasoulifard, Proc. Wrld. Acad. Sci. E. 23 (2007) 267.
9:00 PM - Y3.50
Photocatalytic Activity of ZnO Nanostructured Films Grown by Activated Reactive Evaporation.
Yuvaraj Dhayalan 1 , Narasimha Rao 1
1 Department of Instrumentation, Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractFlower-like ZnO nanostructures were synthesized in the gas phase by plasma assisted reactive evaporation. These gas phase grown nanoflowers were then deposited as nanostructured films at room temperature on substrates like glass, polymer and cotton cloth kept above the plasma source. The structure, morphology and composition of the as prepared films on glass substrates were studied by XRD, SEM, TEM and XPS. Raman and PL studies on the nanostructured films reveal high oxygen deficiency in the film. ZnO nanostructured films grown on different substrates have shown good photocatalytic degradation activity on rhodamine B dye at room temperature. Higher activity of these ZnO nanostructured films is attributed to the higher surface area and oxygen defects present in the films.
9:00 PM - Y3.51
Nanohybrids with Engineered Interfaces for Efficient Catalysis.
Paromita Kundu 1 , Aditi Halder 1 , Anumol Ashok 1 , Ravishankar Narayanan 1
1 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractThe efficiency and reliability of supported catalysts depend on the nature of the support and the catalyst/support interface in addition to the dispersion, size, shape and stability of the catalyst. Typical approaches for producing supported catalysts involve synthesis of catalyst particles and the subsequent dispersion on the supports. While there are methods to attach nearly isotropic/equiaxed particles on supports, the formation of hybrids with anisotropic catalysts remains a challenge. Here, we present a heterogeneous nucleation approach to control the size, shape and dispersion of noble metal catalysts on supports for fuel cell application and quantum dots on a variety of different engineered semiconductor supports for solar cell applications. The method involves attaching an intermediate/precursor phase to the substrate by means of heterogeneous nucleation and subsequently obtaining the desired nanostructures with controlled shape, size and chemistry by using appropriate chemical reactions. We will demonstrate the design of porous ZnO and TiO2 matrices and methods to attach CdS and PbS quantum dots using this approach. We will also show how the method can be used for attaching ultrafine particles of Pt or Pd or catalytically active molecular scale Au nanowires to ZnO and hydroxyapatite nanorods, carbon nanotubes, graphene sheets or porous substrates. The structure, stability and catalytic activity of these hybrids will be demonstrated using a variety of techniques. Primarily we used Electron Microscopy and X-ray Photoelectron Spectroscopy to study the characteristics of synthesized hybrids and Cyclic Voltammetry to investigate their catalytic activities.
9:00 PM - Y3.52
Comparative Study of Single Crystal and Polycrystalline Samaria Doped Ceria Films for Oxygen Sensing.
Rahul Sanghavi 1 , M. Nandasiri 2 3 , S. Kuchibhatla 2 , P. Nachimuthu 2 , M. Engelhard 2 , V. Shutthanandan 2 , W. Jiang 2 , S. Thevuthasan 2 , A. Kayani 3 , S. Prasad 1
1 Department of Electrical Engineering, Arizona State University, Tempe, Arizona, United States, 2 , EMSL, Pacific Northwest National Laboratory, Richland, Washington, United States, 3 Physics Department, Western Michigan University, Kalamazoo, Michigan, United States
Show AbstractPortable and sensitive oxygen sensors are required for applications in automobile industry, wherein, the sensors operate at high temperatures to measure the oxygen concentration at the exhaust systems of the automobiles. Oxygen partial pressure can be used as an input quantity for regulating or controlling systems in order to optimize the combustion process. There is a need to identify, characterize and optimize the material system that would potentially function as the active sensing material for such a device that monitors oxygen partial pressure in these systems. The reduction and oxidation abilities of cerium in ceria nanomaterials under oxygen lean and rich conditions are thus utilized to create oxygen vacancies for oxygen detection in oxygen sensors.We have used thin film samaria doped ceria as the sensing material for the sensor operation, exploiting the fact that at high temperatures, oxygen vacancies generated due to Sm doping act as conducting medium for oxygen ions which hop through the vacancies from one side to the other contributing to an electrical signal. The principle of operation is based on the change in the chemi-impedance of the sensor, defined by a relationship between the oxygen exposure to the active sensing material and the overall conductivity of the sensor at high temperatures.We have recently established that 6 at. % samaria doped ceria film is the optimum composition for highest conductivity. In order to understand the influence of grain boundaries on the sensing properties, we have grown high quality single crystal and polycrystalline films using oxygen plasma assisted molecular beam epitaxy (OPA-MBE) system. The influence of oxygen partial pressure at different temperatures, the dynamic response to the rapidly changing oxygen pressures, hysteresis error measured as the difference in the measured conductivity for different cycles of pressure variations for a constant temperature will be discussed in detail for the material systems.
9:00 PM - Y3.54
Oxygen Reduction Reaction Kinetics on Highly Oriented LSM Thin Films at Intermediate Temperatures.
Ethan Crumlin 1 , Yuki Orikasa 1 , Gerardo Jose la O' 1 , SungJin Ahn 1 , Michael Biegalski 2 , Hans Christen 2 , Yang Shao-Horn 1
1 Electrochemical Energy Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Tallahassee, Florida, United States
Show AbstractLa0.8Sr0.2MnO3 (LSM) is a common catalyst for oxygen reduction reaction (ORR) in high temperature solid oxide fuel cells. A large number of thin film studies have reported ORR activity on polycrystalline LSM. However, the effects of LSM surface crystallographic orientations on ORR activity are not understood. In this study, LSM thin-films were grown via pulsed-laser deposition on single crystal 9.5% Y2O3-stabilized ZrO2 having the (100), (110), or (111) orientation with a 20% Gd-doped CeO2 interlayer. Out-of-plane X-ray diffraction was used to estimate relative fractions of the surface crystallographic orientations. The surface morphologies of the samples were investigated using atomic force microscopy, where minimal changes in the film surface were found before and after testing to temperatures below 600°C. Rutherford-backscattering analysis showed that the film bulk composition was stoichiometric while X-ray photospectroscopy of the film surface composition revealed that La and Sr were enriched slightly with respect to Mn. To investigate the ORR activity of the LSM films, the films were patterned into microelectrodes having sizes in the range from 25 μm to 200 μm. These microelectrodes were tested using electrochemical impedance spectroscopy from 500°C to 700°C and in the oxygen partial pressure range from 10-4 atm to 1 atm. The influences of substrate orientation on LSM thin-film ORR activity and rate-limiting reactions will be discussed.
9:00 PM - Y3.55
Catalysis at the Liquid/Solid Interface: Catalyst Synthesis by Atomic Layer Deposition and in Situ Characterization by Surface-Enhanced Raman Spectroscopy.
Kathryn Kosuda 1 , Peter Stair 1 2 , Richard Van Duyne 1
1 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractCatalytic reactions that occur at the liquid/solid interface are of great importance in heterogeneous catalysis, particularly in the processing of biomass to fuels. To better understand the binding and reaction of surface adsorbates, in situ characterization techniques are needed that can identify surface species in aqueous solution. Surface-enhanced Raman spectroscopy (SERS) is ideally suited for such measurements because of its superior surface sensitivity as well as its compatibility with water. Atomic layer deposition (ALD) is a thin film growth technique based on the alternating use of self-limiting reactions between gaseous precursor molecules and a substrate to deposit materials with atomic level precision. The high uniformity and size control afforded by ALD as well as the variety of metal oxide and metallic materials that can be grown make ALD a versatile technique for synthesizing nanostructured catalysts. In this work, ALD is used to synthesize various catalysts over Ag SERS substrates. Ultrathin metal oxide layers improve the thermal and solvent stability of Ag SERS substrates, thus enabling measurements in catalytically relevant liquids like water and ethanol at elevated reaction temperatures. SERS is used to study the nature of adsorbed reactants and intermediates on the catalyst surface, demonstrating the potential of SERS as a powerful tool for in situ studies of catalysis at the liquid/solid interface.
9:00 PM - Y3.56
Characterization of Pore Framework Structure in Monolithic Mesoporous Silica.
Ching-Mao Wu 1 , Szu-Yin Lin 1 , Chin-Cheng Weng 1 , Kuo-Tung Huang 1
1 Material and Chemical Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu Taiwan
Show AbstractMesoporous silica materials have received much interest due to commercial applications in chemical separations and heterogeneous catalysis. Recent studies have reported via a sol-gel nanocasting technique, monolithic mesoporous silica with wormlike pore framework could be prepared by utilizing room-temperature ionic liquids (RTILs) as templates and solvents. Although previous reports have indicated that the wormlike pores would be formed in the silica, the detailed pore network structure still remained the crucial issues to be resolved. In the present study, we investigated the pore structure in the monolithic mesoporous silica, which was templated by RTIL (1-butyl-3-methyl-imidazolium-tetrafluoroborate). We revealed an open fractal pore network with a branched and self-similar appearance was formed by the aggregation of the individual spherical pores. Transmission electron microscopy micrographs displayed that the disordered wormlike pore framework was formed in the silica. Furthermore, the small angle X-ray scattering profile measured herein further exhibited three distinct regions of power-law scattering on the respective length scales. In the high-q region, the profile followed Power behavior and a power-law of -4 was observed for the surface fractal dimension of 2, manifesting the primary pore with a smooth surface and a spherical appearance. In the intermediate-q region, a power-law of -2.5 (mass fractal dimension of 2.5), indicating an open mass fractal network was formed by the aggregation of the individual primary pores. Moreover in the low-q region, the power-law of -4 was observed for mass-fractal agglomerates of aggregates. With the proceeding analysis of unified equation in terms of two structural levels, the radiuses of gyration of primary pore (Rg1) and its aggregates (Rg2) were fitted as ca. 0.9 nm and 5.5 nm, respectively. For a spherical-model pore, the radius of pore (R) was ca. 1.16 nm; thus, the averaged pore diameter (D) was 2.32 nm. The number of primary pores in a fractal aggregate (degree of aggregates, z) was calculated as ca. 67.
9:00 PM - Y3.57
Preparation of Sulfur Containing Ordered Mesoporous Carbons for Catalytic Application.
Jin Hoe Kim 1 3 , Jeong Ah Yoon 1 3 , Eun Joo Park 1 3 , Jeong Kuk Shon 1 3 , Ji Man Kim 1 2 3
1 Chemistry, Sungkyunkwan University, Suwon Korea (the Republic of), 3 BK21 School of Chemical Materials Science, Sungkyunkwan University, Suwon Korea (the Republic of), 2 SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon Korea (the Republic of)
Show Abstract Many research groups study in functionalization of ordered mesoporous materials such as silica, carbon and metal oxide. There are two classes of method for surface functionalization by one or two-step functionalization. One-step method is promoted by precursor which has hetero element in synthesis procedure and two-step approach is post treatment with active gases on prepared material’s surface. These materials show enhanced properties that thermal stability, conductivity, fire resistance, sorptivity, and these functional groups are easy to modify to other one. Especially, sulfur containing materials used to heavy metal sorbents, capacitance materials, and solid acid catalyst. We have chosen one-pot synthesis strategy for fabrication of sulfur containing mesoporous carbon(S-OMC) by nano-casting method with p-toluenesulfonic aicd as sulfur containing precursor. According to this method, we fabricate mesoporous carbon which has high specific surface area and heteroatomic functionality. These materials are easy controlled the content of sulfur element in the mesoporous carbons by controlling carbonization temperature. And this synthesis method is less toxic than other synthesis method due to it isn’t need to polymerization catalyst such as sulfuric of phosphoric acid.
9:00 PM - Y3.59
Single Crystalline La1-xSrxMnO3 Microcubes for Electrocatalysis of Oxygen Reduction.
Mingjia Zhi 1 , Nianqiang Wu 1
1 Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia, United States
Show AbstractLa1-xSrxMnO3 (LSM) microcubes were synthesized by hydrothermal methods. X-ray diffraction (XRD) analysis shows that the microcubes have a perovskite structure. The transmission electron microscopy (TEM) analysis has confirmed that the microcubes are single crystals with the exposed surface terminated with (200) facet. The electrocatalytic activity toward oxygen by the LSM microcube was investigated with DC polarization and impedance spectroscopy from 973K to 1173K under different O2 partial pressures. The activation energy for oxygen reduction of the microcubes sample was lower than that of conventional polycrystalline LSM powder samples in atmosphere air. The detail reaction kinetics was investigated and the rate limit step for oxygen reduction was determined. The origin of the electrocatalytic behavior of the LSM single crystal cubes and polycrystalline powder was discussed. Long term cathodic polarization experiment was carried out to evaluate the stability of the LSM microcubes as a potential cathode material for solid oxide fuel cells.
9:00 PM - Y3.6
Reactivity Studies at the Surface of Ruthenium Nanoparticles - An Approach to Fischer-Tropsch Process.
Fernando Novio 1 , Karine Philippot 1 , Bruno Chaudret 1
1 , Laboratoire de Chimie de Coordination. CNRS, Toulouse France
Show AbstractMetal nanoparticles have been used for a long time to catalyze chemical reactions in both heterogeneous and homogeneous phases.[1] The different techniques used in analysis of traditional heterogeneous and homogeneous catalysis are difficult to combine for the study of metal nanoparticles. Thus, many questions concerning the reactivity of metal nanoparticles are still open, particularly the nature of intermediate surface species.In our team, metal nanoparticles are synthesized by hydrogenation of organometallic precursors in the presence of organic ligands as stabilizers (amines, phosphines, or others).[2] Very small and monodisperse ruthenium nanoparticles can be obtained by this route that display well-controlled surface state. This makes them interesting systems for studying surface reaction mechanisms by a combination of analytical techniques like IR and NMR spectroscopies.[3] We are interested in understanding the surface reactions related to Fischer-Tropsch (FT) process including CO activation, CXHY hydrogenation, hydrocarbon coupling and termination pathways. In this sense Ru presents an optimal position since FT activity decreases dramatically in the order Ru, Fe, Co, Rh, Ni, Pd and Pt.[4] Moreover, Ru also produces selectively very high weight hydrocarbons. Although diverse mechanisms are proposed for FT reaction,[5] the controlling reaction mechanism is still actively debated. We will thus report our recent results in the study of CO behavior at Ru particle surface in the presence of various substrates arising from a combination of diverse analytical techniques, like NMR investigations. In particular, different coordination modes of CO, depending on the coverage ratio, and its reaction with different species coordinated at the nanoparticle surface are observed. [1] a) A. Roucoux, K. Philippot in Hydrogenation with Noble Metal Nanoparticles in Handbook of Homogenous Hydrogenations (Ed.: G. de Vries), Wiley-VCH, Weinheim, 2007, pp. 217–256; b) M. T. Reetz, E. Westermann, Angew. Chem. 2000, 12, 170–173; Angew. Chem. Int. Ed. 2000, 39, 165–168; c) M. Moreno-Mañas, R. Pleixats, S. Villarroya, Organometallics 2001, 20, 4524–4528; d) C. C. Cassol, A. P. Umpierre, G. Machado, S. I. Wolke, J. Dupont, J. Am. Chem. Soc. 2005, 127, 3298–3299; e) D. Astruc, F. Lu, J. R. Aranzaes, Angew. Chem. 2005, 117, 8062–8083; Angew. Chem. Int. Ed. 2005, 44, 7852–7872; f) J. G. de Vries, Dalton Trans. 2006, 42, 1–429.[2] a) K. Philippot, B. Chaudret, C. R. Chim. 2003, 6, 1019–1034; b) B. Chaudret, Top. Organomet. Chem. 2005, 16, 233–259.[3] T. Pery, K. Pelzer, G. Buntkowski, K. Philippot, H.-H. Limbach, B. Chaudret, ChemPhysChem 2005, 6, 605–607. Angew. Chem. Int. Ed. 2008, 47, 2074–2078.[4] M. A. Vannice, J. Catal., 1977, 50, 228-236.[5] a) M. L. Turner, N. Marsih, B. E Mann, R. Quyoum, H. C. Long, P. M. Maitlis, J. Am. Chem. Soc. 2002, 124, 10456-10472. b) I. M. Ciobica, G. J. Kramer, Q. Ge, M. Neurock, R. A. van Santen, J. Catal., 2002, 212, 136-144.
9:00 PM - Y3.60
Structural, Morphological and Photoelectrochemical Behavior of Hematite Modified by 120 MeV Ag9+ Ions.
Aadesh Singh 1 , Saroj Kumari 2 , Rohit Shrivastav 3 , Sahab Dass 4 , Vibha Satsangi 5
1 Department of Physics & Computer Science, Dayalbagh Educational Institute, Agra, Uttar Pradesh, India, 2 Department of Physics & Computer Science, Dayalbagh Educational Institute, Agra, Uttar Pradesh, India, 3 Department of Chemistry, Dayalbagh Educational Institute, Agra, Uttar Pradesh, India, 4 Department of Chemistry, Dayalbagh Educational Institute, Agra, Uttar Pradesh, India, 5 Department of Physics & Computer Science, Dayalbagh Educational Institute, Agra, Uttar Pradesh, India
Show AbstractHigh energy heavy ion irradiation provides the researchers a new dimension to introduce the desired changes in the behaviour of the material, which largely influence their properties. Nanostructured hematite thin film for photoelectrochemical (PEC) splitting of water has great potential in the design of low-cost, environmental friendly solar-hydrogen production. Presently, solar-to-hydrogen conversion efficiency of PEC cell using iron oxide is limited by its poor charge transport due to high recombination losses and mismatch of band edges position with the redox level of water. In order to get efficient PEC system, spray-pyrolytically deposited nanostructured hematite thin films were modified by irradiating the samples with 120 MeV Ag9+ ions with fluences ranging from 5x1011 to 1x1013 ions cm-2. Irradiated samples exhibited a transition from the hematite to the magnetite phase and reduction in particle size as indicated by XRD and Raman analysis. TEM picture showed a decrease the thickness and porosity of the films after irradiation. These irradiated films, when used in PEC cell showed significantly higher photocurrent density than unirradiated α-Fe2O3.
9:00 PM - Y3.61
Synthesis of Electrospun Indium Oxide Materials for Photocatalytic Applications.
Ellen Steinmiller 1 , Kun Ha Park 1 , Sara Skrabalak 1
1 Chemistry, Indiana University , Bloomington, Indiana, United States
Show AbstractThe development of new photocatalysts for solar energy conversion is critical to meeting the ever increasing demand for energy. One strategy for improving the performance of semiconductor-based photocatalysts is to couple two semiconductors with appropriate electronic structures together in order to provide enhanced electron-hole separation. Electrospinning is an attractive synthetic method for the development of semiconductor fibers, with the final morphology of the fibers being easily tuned by manipulating system parameters such as applied potential, spin rate, working distance. Furthermore, composite semiconductors can be facilely achieved by either controlling the solution components prior to electrospinning or during the electrospinning process. This presentation will discuss electrospun In2O3 fibers and electrospun In2O3:TiO2 composite fibers. In2O3 fibers were prepared by electrospinning solutions of indium nitrate, ethanol, and polyvinylpyrrolidone (PVP). Prepared fibers are amorphous, but can be converted to crystalline In2O3 by calcining at 500°C. Composite In2O3: TiO2materials were prepared by either utilizing a side by side spinneret system in which one side contained the In2O 3 precursor and the other the TiO2 precursor (titanium (IV) isopropoxide, acetic acid, and PVP) or by combining the In2O3 precursor and a TiO2 precursor before electrospinning. The observed photocatalytic activity of the prepared samples during methylene blue degradation will be discussed as a function of the individual and composite features and compared to photocatalysts prepared by conventional methods. Additionally, these materials will be explored for their potential water splitting capabilities.
9:00 PM - Y3.63
Thermally Stable Nanocrystalline Mesoporous Gallium Oxide Phases.
Chinmay Deshmane 1 , Moises Carreon 1
1 Chemical Engineering, University of Louisville, Louisville, Kentucky, United States
Show AbstractGallium oxides and gallium-based oxides are of great interest in the field of heterogeneous catalysis. Gallium oxide is a well known strong acid catalyst. Ga2O3-based catalysts are active in the dehydrogenation of light alkanes and in the selective catalytic reduction of NOx by hydrocarbons in the presence of oxygen. Supported gallium oxides are preferred over zeolites in the de-NOx reaction because of their acidity. These catalysts are also effective in the aromatization of ethane in the presence of CO2. Different polymorphs of gallium oxide have been employed for the dehydrogenation of alkanes to alkenes.Recently, gallium oxide has been studied as catalyst in the epoxidation of cyclooctene in the presence of hydrogen peroxide.Gallium oxide has been synthesized using diverse techniques, such as thermal decomposition, homogeneous precipitation using ammonia, and surface layer adsorption. However, these methods offer poor control over structural, morphological and compositional properties. It has been prepared in nanowire form by a number of techniques, including arc-discharge, vapor-liquid-solid (VLS), carbothermal reduction, and thermal oxidation. All these methods produced crystalline Ga2O3 nanowires with relatively low specific surface areas. Furthermore, these techniques are complex, time consuming and costly. Herein, we present the synthesis of thermally stable mesoporous gallium oxide employing, Evaporation-Induced Self-Assembly (EISA) and Self-Assembly Hydrothermal-Assisted (SAHA) approaches.[1] These methods not only eliminate the need for high synthesis temperatures commonly required for solid-state reactions, but also offer the possibility to synthesize thermally stable mesoporous oxides with controlled morphological, textural and structural properties. EISA led to partially crystalline mesoporous gallium oxide phases displaying unimodal pore size distribution in the ~2-5 nm range and surface areas as high as 300 m2/g. SAHA led to nanocrystalline mesoporous uniform micron-sized gallium oxide spheres (~0.3-6.5 μm) with narrow size distribution displaying cubic spinel type structure. These mesophases displayed surface areas as high as ~221 m2/g and unimodal pore size distribution in the ~5-15 nm range. Textural properties such as surface areas and pore sizes were effectively fine-tuned by the nature and relative concentration of the structure directing agents. Due to their high surface areas, tunability of pore sizes and the nature of the wall structure, these gallium oxide mesophases could find potential applications as heterogeneous catalysts. [1] C.A. Deshmane, J.B. Jasinski, M.A. Carreon, Eur. J. Inorg. Chem. 2009, in press, DOI: 10.1002/ejic.200900359
9:00 PM - Y3.64
Self Assembly Hydrothermal Assisted Synthesis of Mesoporous Anatase in the Presence of Ethylene Glycol.
Amruta Katti 1 , Surendar Venna 1 , Moises Carreon 1
1 Chemical Engineering, University of Louisville, Louisville, Kentucky, United States
Show AbstractDecolorization of effluents from textile dyeing and finishing industry, is of great interest because of aesthetic and environmental concerns. Dyes even in low concentration are visually detected and affect the aquatic life and food web. Because of the potential toxicity of these substances and their visibility in surface waters, removal or degradation of organic dyes has been a matter of considerable interest. TiO2 has been recognized as the ideal photocatalyst for the destruction of common organic pollutants in textile industry because of its biological and chemical inertness, stability towards photochemical and chemical corrosion, an electronic band gap that upon photoexcitation creates highly oxidizing holes, high recombination rate of photogenerated electron–hole pairs and highly reducing electrons. Herein we present the synthesis of mesoporous nanocrystalline titania employing a modified self-assembly approach, namely self-assembly hydrothermal-assisted (SAHA) approach.Mesoporous nanocrystalline anatase was prepared hydrothermally employing P123 as structure directing agent. Ethylene glycol was used as a key synthesis parameter to fine tune the morphology, crystal size and pore size of the resultant mesophases. The incorporation of EG in the synthesis gel resulted in the formation of 1-2 µm sphere-like shapes and led to an increase in the specific surface area from ~95 m2/g to ~170 m2/g, decrease in the average pore size from ~11 nm to ~4.8 nm, and decrease in the average crystallite size from ~17 nm to ~12 nm. These mesophases were used as photocatalysts for the UV degradation of methylene blue and methyl orange. The mesoporous anatase phases photodegraded MB ~ 1.5-3 times faster than commercially available DP25 and showed limited photocatalytic behavior for methyl orange.
9:00 PM - Y3.7
High Activity of Amorphous Potassium in Pt/K/Al2O3 NOx Storage-reduction Catalysts.
Robert Buechel 1 , Alfons Baiker 2 , Sotiris E. Pratsinis 1
1 D-MAVT, ETH Zurich, Zurich Switzerland, 2 D-CHAB, ETH Zurich, Zurich Switzerland
Show AbstractTo meet upcoming stricter emission limits new catalysts for NOx removal are development. Today, the main challenge is to reduce NOx under oxygen rich conditions as encountered in lean burn and direct injection engines. NOx storage-reduction (NSR) catalyst can trap exhaust NOx under fuel lean conditions on alkali- or alkaline earth metals in the form of metal-nitrates whereby K and Ba are reported to be the best. The NOx trap is regenerated during a short fuel rich period, where the metal-nitrates are decomposed and the released NOx are reduced to nitrogen. Potassium and barium have been studied extensively for their NOx storage and regeneration behavior whereby K showed higher performance especially at elevated temperatures. Furthermore K2CO3 is less toxic and cheaper than BaCO3. Here, we prepared Pt/K/Al2O3 catalysts using a twin flame spray pyrolysis (FSP) setup [1] allowing to separate synthesis of the support and storage components of the NSR catalyst [2]. This setup also allows controlling the location of Pt-clusters on the support or the storage sites of the NSR catalysts [3]. Raman investigations showed amorphous K2CO3 to be present, exhibiting a higher NOx conversion compared to Ba at high as well as low temperatures. The K concentration is a crucial factor for the steady-state NOx conversion efficiency of a given fuel lean/rich cycle length. An advantage of the K based catalysts was that during the switch from fuel lean to fuel rich the typical undesired overshooting of the NOx was decreased for higher temperatures. The superior performance was attributed to good K distribution in the sample as evidenced by STEM combined with EDX analysis. Preferential Pt deposition on K increased the catalyst efficiency, especially during the reduction phase. In contrast to flame made BaCO3 which transforms from orthorhombic to monoclinic structure, amorphous K2CO3 showed no measurable crystal change and stayed stable even during TGA measurements up to 1000°C. References[1]R. Strobel, L. Madler, M. Piacentini, M. Maciejewski, A. Baiker, S.E. Pratsinis, Chem. Mater. 18 (2006) 2532-2537.[2]M.O. Symalla, A. Drochner, H. Vogel, R. Büchel, S.E. Pratsinis, A. Baiker, Appl. Catal., B 89 (2009) 41-48.[3]R. Büchel, R. Strobel, F. Krumeich, A. Baiker, S.E. Pratsinis, J. Catal. 261 (2009) 201-207.
9:00 PM - Y3.8
Analysis of High Resolution C 1s X-ray Photoelectron Spectra of Mo2C Powders.
Robert Savinelli 1 , Susannah Scott 1 2
1 Chemistry, University of California, Santa Barbara, California, United States, 2 Chemical Engineering, University of California, Santa Barbara, California, United States
Show AbstractCarbon deposition poses a significant challenge to the performance of many heterogeneous catalysts. Surface contaminates are often a mixture of partially oxidized, graphitic, and amorphous carbon. The relative amount of each can depend on catalyst preparation, handling, and usage. Transition metal carbides (TMC) exhibit catalytic activities which are similar to noble metals and have shown resistance to CO and SO2 poisoning. Carbon deposition is a major deactivation pathway for these catalysts. It is valuable to know which carbon phases are present near the catalyst surface in order to develop effective coke prevention and or catalyst regeneration strategies. X ray photoelectron spectroscopy (XPS) has had limited success for the analysis of surface carbon due to the presence of overlapping C 1s components and adventitious carbon. Reported C 1s binding energies (BE) and component widths (FWHM) of related materials are not in agreement due to differences in instrumentation, calibration, charging, and sample selection. XPS was used to investigate the near surface carbon composition of Mo2C powders prepared by temperature programmed carburization, in a carbon rich atmosphere, from ammonium paramolybdate. Rigorous analysis of the C 1s spectra revealed a consistent approach for determining the relative amount of carbonate (C=O, C-O), amorphous (a-C-C), graphite (g-C-C), oxycarbide (C-Mo-O), and carbide (C-Mo) carbon for a broad distribution of carbon contaminated Mo2C surfaces. Precise BE and FWHM were assigned after careful BE calibration, and use of component parameters from spectra with minimal overlap. BE were referenced to high resolution spectra of the Fermi energy and were internally consistent with Au 4f and Mo 3d BE shifts. C-Mo and g-C-C fitting parameters were determined from samples with clearly resolved C-Mo components and from pure graphite respectively. BE assignments are similar the literature though FWHM are narrower (≥0.55 eV) due to the monochromatic X-rays and a low detector pass energies (10 eV) used, Table 1. Narrow FWHM are necessary to resolve the C-Mo-O and C-Mo components which have BE separated by less than 1 eV. Many of these spectra could not be fit using the known component parameters and a five component model. This issue was resolved by the addition of another component, C-Mo-O, between the g-C-C and C-Mo components. A significant amount of C-Mo-O (up to 27%) was measured in the spectra of certain samples. Among all the samples, the total carbon atom percent varied from 30 to 82%. The relative C-Mo, g-C-C, and a-C-C compositions were from 9% – 52%, 4% - 72%, and 10% - 51% respectively. C-Mo-O rich powders have an additional signal intensity in the O 1s spectra.
9:00 PM - Y3.9
A Study of NixPy/CeO2 Catalysed Autothermal Reforming of N-octane.
Lei Liu 1 , Liang Hong 1
1 , National University of Singapore, Singapore Singapore
Show AbstractAbstractAutothermal reforming (ATR) of fossil fuels will be a promising technique for the production of hydrogen for fuel cell use because of its thermodynamic self-sustainability. In this work, we report an investigation of ATR of n-octane using the CeO2-supported NixPy catalyst, which was prepared by electroless nickel plating. NixPy represents the compound (x/y = 3.7) formed. For comparison purpose a Ni/CeO2 catalyst was prepared by the impregnation method. The investigation was carried out under the optimum operating conditions (i.e. O2/C =0.5; H2O/C =1.7, air-H2O(g)-octane feed GHSV = 9,000 ml/h/gcat, and at 900 deg.C). The two catalysts although displayed similar performance over an evaluation of 8 hours, a heavy growth of carbon whisker was identified on the Ni/CeO2 reference, in contrast, the NixPy /CeO2 catalyst was completely free of coking. The catalysts were characterized by XPS and TPR, relative to the known interaction between Ni and CeO2, the valence electronic structure and reducibility of Ni in NixPy is more strongly affected by the formation of the compound with P. Such interaction is deemed to be responsible for the prevention of carbon deposition. Keywords: Hydrogen; Autothermal reforming; Carbon deposition; Electroless nickel plating; n-Octane
Symposium Organizers
Sheng Dai Oak Ridge National Laboratory
Harold H. Kung Northwestern University
Jun Liu Pacific Northwest National Laboratory
Chung-Yuan Mou National Taiwan University
Y4
Session Chairs
Victor Lin
Chung-Yuan Mou
Tuesday AM, December 01, 2009
Room 311 (Hynes)
9:30 AM - **Y4.1
The Development of Routes to New Zeolite Materials Which Can Be Compatible With Commercialization For Environmental Process Technology.
Stacey Zones 1
1 , Chevron Energy and Tech., Richmond, California, United States
Show AbstractZeolite Molecular Sieves have seen a large scale commercial deployment in refining and petrochemicals in the second half of the 20th Century. Meanwhile exploratory research has generated a large number of newer molecular sieve structures, including materials based upon metal-organic frameworks ( MOF's ) with very high void volumes but selective pore sizes. Other new matrerial have emerged from the use of germanium into the silicon synthesis chemistry. WHile both of these breakthrough approaches have generated greater numbers of newer structures, one of the challenges which remains is how to match the new material with the right application and then find a commercially feasible approach to making a desired material once the use has been found. In this presentation I will try to link some of the pieces along this continuum of discovery of material, discovery of application to route of synthesis
10:00 AM - Y4.2
In-Situ Optical Imaging of Single Nanoparticle Catalysis at Single-Turnover Resolution.
Peng Chen 1
1 Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
Show AbstractMetal nanoparticles can catalyze many chemical transformations for energy conversion, petroleum processing, and pollutant removal. Charactering their catalytic activity is important, but challenging in ensemble measurements due to their morphology dispersions and variable surface active sites. Using single-molecule microscopy of fluorogenic reactions, we monitor the redox catalytic reactions on the surface of individual Au-nanoparticles in an aqueous environment in real time at single-turnover resolution. We find that for catalytic product generation, all Au-nanoparticles follow a Langmuir-Hinshelwood mechanism, but individual nanoparticles show drastically different reactivity. And for product dissociation, three nanoparticle subpopulations are present that show differential selectivity between parallel dissociation pathways. Individual nanoparticles show large temporal activity fluctuations, attributable to both catalysis-induced and spontaneous dynamic surface restructuring that occurs at different timescales at the surface catalytic and product docking sites. Individual Au-nanoparticles also show reactant-concentration dependent dynamic surface switching between a low reactivity state and high reactivity state. Strong size dependences are also observed in the catalytic activity, selectivity, and dynamics of these Au-nanoparticles. Smaller particles are more reactive but bind the reactant weaker. Larger particles are less selective in the parallel reaction pathways. The smaller particles are more prone to dynamic surface restructuring, whose activation energies and timescales are quantified. The results exemplify the power of the single-molecule approach in revealing the interplay of catalysis, heterogeneous reactivity, and surface structural dynamics in nanocatalysis.References: (1) W. Xu, J. S. Kong, Y.-T. E. Yeh, P. Chen "Single-Molecule Nanocatalysis Reveals Heterogeneous Reaction Pathways and Catalytic Dynamics" Nature Materials 2008, 7, 992-996. (2) W. Xu, J. S. Kong, P. Chen "Single-Molecule Kinetic Theory of Heterogeneous and Enzyme Catalysis" Journal of Physical Chemistry C, 2009, 113, 2393-2404. (3) W. Xu, J. S. Kong, P. Chen "Probing the Catalytic Activity and Heterogeneity of Au-Nanoparticles at the Single-Molecule Level" Physical Chemistry Chemical Physics 2009, 11, 2767-2778. (4) P. Chen, W. Xu, X. Zhou, D. Panda, A. Kalininskiy "Single-Nanoparticle Catalysis at Single-Turnover Resolution" Chemical Physics Letter 2009, 470, 151-157.
10:15 AM - Y4.3
X-ray Atomic Imaging of Supported Mixed Catalyst VOx-WOx / α-TiO2 (110) During a Redox Cycle.
Zhenxing Feng 1 , Jeffrey Elam 2 , Zhan Zhang 2 , Chang-Yong Kim 3 , Michael Bedzyk 1 2
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 , Argonne National Lab, Argonne, Illinois, United States, 3 , Canadian Light Source, Saskatoon, Saskatchewan, Canada
Show AbstractMetal-oxide monolayers deposited on oxide surfaces have applications in catalysis and chemical sensing. Supported mixed catalysts (VOx/WOx/α-TiO2(110)) are of particular interest. If the atomic-scale geometrical and electronic surface structure of mixed VOx and WOx could be predicted, this would impact our understanding of numerous complex chemical processes. As a model catalytic system, atomic layer deposition (ALD) was used to grow VOx and WOx on α-TiO2(110). AFM was used to study the surface morphological changes. X-ray fluorescence and in situ X-ray standing waves (XSW) were used in combination to determine the geometric structure changes during the redox reaction. The XSW results for 1.1 ML V on 0.7 ML W show that V cations on the surface occupy different positions in the oxidized and reduced states, while W cations show no redox-induced changes. In situ XSW measured atomic density maps show that these adsorption sites are different from just vanadia on the rutile surface. X-ray photoelectron spectroscopy (XPS) is used to correlate the V and W oxidation state(s) with the above redox induced structural changes. A model is proposed to explain the reversible geometrical/electronic structure changes during this redox reaction. This study is related to our earlier study of the ALD grown 0.3 ML WOX/α-TiO2(110) interface.[1][1] C. Y. Kim, J. W. Elam, M. J. Pellin, D. K.Goswami, S. T.Christensen, M. C.Hersam, P. C. Stair, M. J, Bedzyk, J. Phys. Chem. B 110, 12616 (2006).
10:30 AM - Y4.4
Plasmonics Meets Catalysis: A Novel Highly Versatile Remote Sensing Technique to Monitor Catalytic Reactions.
Elin Larsson 1 , Christoph Langhammer 1 , Igor Zoric 1 , Bengt Kasemo 1
1 Applied Physics, Chalmers University of Technology, Gothenburg, Sweden Sweden
Show AbstractWe report a new “nanoplasmonic” (localized surface plasmon resonance, LSPR) method that with a remarkably simple optical transmission (or reflection) measurement can sensitively follow catalytic reactions in real time and can be applied to both model catalysts and real supported catalysts at atmospheric pressure. Many industrial processes as well as the environmental and energy sectors depend on catalysis. To understand and improve heterogeneous catalyst systems it is important to be able to monitor the catalyst’s state (e.g. reactant coverage or oxidation state) and to follow the reaction in real time. However, there is still a need of new experimental probes that allow such investigations to be made on the often complex catalyst structures and under real reaction conditions. The technique presented here is suitable for use in harsh environments and in a remote sensing set up. The principle is “nanoplasmonic” sensing, which has been intensely investigated for biosensing. The plasmon excitation causes a peak in the optical extinction versus wavelength spectrum. The peak position, λmax, measured in the experiment, is sensitive to surface changes of e.g. catalyst particles in the near (nm) proximity of the plasmonic particle. We show that LSPR sensing can be used to detect coverage changes on Pt clusters (ca. 12nm in diameter), with a sensitivity of less than 0.1 monolayers of oxygen during oxidation of H2 or CO. Additionally, we show that NOx storage and release from BaO (commonly used in NOx storage catalysts) can be monitored using this technique [1]. We predict that nanoplasmonic sensing of catalytic reactions on supported and model catalysts will open up a new field in catalysis research and may provide new sensors e.g. for the automotive industry. The same "nanoplasmonic" sensing scheme has also be applied to monitor hydrogen absorption and desorption from palladium clusters (1-10nm) [2].1. E. M. Larsson, C. Langhammer, I. Zoric, B. Kasemo , Nanoplasmonics meets catalysis, Submitted to Science2. C. Langhammer, E. M. Larsson, B. Kasemo, I. Zoric, Localized surface plasmons: shedding light on nanoscale hydrogen storage system
11:30 AM - **Y4.6
Understanding the Factors Controlling Catalyst Activity and Selectivity Through the Use of In Situ Spectroscopy and Multi-Scale Simulation.
Alexis Bell 1
1 Department of Chemical Engineering, University of California, Berkeley, California, United States
Show AbstractIt is well recognized that the composition and structure of catalysts affect their activity and selectivity. For the most part, an understanding of composition/structure-activity/selectivity relationships has come from experimental data of various types. In recent years, though, theoretical methods have developed to the point where meaningful interpretations of experimental can be carried out, as well as simulations of reaction kinetics, and the overall performance of microporous catalysts, including the effects of diffusional mass transfer. This talk will illustrate how a comprehensive understanding of complex reaction systems can be obtained by combining measurement of reaction kinetics, in situ spectroscopic observations, quantum chemical calculations, and the principles of chemical reaction engineering. The examples discussed will include various examples of reactions relevant to fuels and chemicals production. The take home message of this presentation will be that a much deeper understanding of how the performance of a catalyst is related to it composition and structure can be obtained by combining experimental and theoretical methods.
12:00 PM - Y4.7
Optimal Design of Catalysts via Multiscale Modeling: Application to Hydrogen Production.
Zachary Ulissi 1 , Vinay Prasad 1 , Jonathan Sutton 1 , Dionisios Vlachos 1
1 Chemical Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractFundamental multiscale models are increasingly being used to describe complex systems. Microkinetic models, which consider a detailed surface reaction mechanism containing all relevant reactions, are prototypical multiscale models. These multiscale microkinetic models employ results from fundamental techniques such as density functional theory (DFT) and transition state theory (TST), along with semi-empirical methods such as bond order conservation (BOC), and couple them with larger scale models (kinetic Monte Carlo or mean field, and reactor scale models) to build predictive models. The predictive capabilities of these models make them suitable candidates for catalyst design. In this work, we describe a novel optimization-based technique, which calculates the optimal values required for atomic descriptors (e.g., binding energies of adsorbates), and then calculates alloys or single metal catalysts that best approach the optimal values. A key advantage of this method is that the models used account explicitly for the coupling between the atomic scale descriptors and the macroscale environment (type of reactor, operating conditions), leading to the optimal design of catalysts under actual conditions of operation. We demonstrate the overall framework for the ammonia decomposition reaction for hydrogen production. Extension of the modeling framework to complex bifunctional, bimetallic catalysts will be presented and comparison to temperature programmed desorption experiments will be shown.
12:15 PM - Y4.8
The Dimensionality of Au/TiO2(110) Nanoparticles During the Catalytic Oxidation of CO, as Determined By in situ Grazing Incidence Small Angle X-ray Scattering (GISAXS).
Marie-Claire Saint-Lager 1 , Aude Bailly 1 , Miguel Mantilla 2 , Stephanie Garaudee 1 , Remi Lazzari 2 , Pierre Dolle 1 , Odile Robach 3 , Jacques Jupille 2 , Issam Laoufi 1 , Pierre Taunier 1
1 , Institut Neel, Grenoble France, 2 , Institut des Nanosciences de Paris, Paris France, 3 , Nanosctructures et Rayonnement Synchrotron, CEA, Grenoble France
Show AbstractThe catalytic activity of supported gold nanoparticles [1] has generated great excitement over the two last decades and it is still debated. Although bulk gold is mostly inert, the activity of gold particles increases dramatically as their size decreases [2]. A maximum in reactivity (molecule per gold atom per second) has been observed for the oxidation of CO on Au/TiO2(110) clusters of 2.5 to 3 nm in diameter D [3]. It was attributed to a quantum size effect with a maximum in activity for two-atoms-thick clusters [4], though this effect was later questioned on the basis of a vibrational study of the CO/Au films of various thicknesses [4]. In a much different way and in the same spirit as the earlier suggestion that the reactivity of gold nanoclusters is a peripheral property [5], it was concluded from density functional approaches that the activity of gold nanoparticles mostly comes from low coordinated atoms [6].To date, a direct characterization of the morphology of gold nanoclusters during catalytic reactions is lacking. The present works reports on observations by Grazing Incidence Small Angle X-Ray Scattering (GISAXS) of Au/TiO2(110) supported particles during the catalytic oxidation of CO, by using a dedicated set up. The analysis chamber, operated from ultra-high vacuum to normal pressure, is acting as a reactor [7]. The reactivity is determined by mass spectrometry. In the present case (20 mbar O2 + 0.1 mbar CO on Au/TiO2(110) at 200 K), it rapidly increases for particles < 5 nm. GISAXS demonstrates that reacting gold particles are always three-dimensional with an aspect ratio H/D ≈ 0.6 (H is the height of the particles) which, for the smallest particles under study (D = 2 nm) still corresponds to 5 atomic layers of gold. The reaction mechanism is discussed via the relationship between the reactivity and the particle size.[1] M. Haruta et al., Chem. Lett. 2 (1987) 405.[2] F. Bocuzzi et al., J. Phys. Chem. 100 (1995) 3625.[3] M. Valden et al., Science 281 (1998) 1647.[4]. C. Lemire et al., Angew. Chem., Int. Ed. 43 (2004) 118.[5] M. Haruta et al., J. Catal. 144 (1993) 175.[6] N. Lopez et al., J. Catal. 223 (2004) 232.[7] M.-C. Saint-Lager et al., Rev. Sci. Instrum. 78 (2007) 083902.
12:30 PM - Y4.9
Electron Photoinjection from Ru Complexes Bound to Shortened Multilayered Titania Nanotubes Through Manipulation of Band Edge Energy Levels by Li Intercalation.
Gregory Mogilevsky 1 , Jacob Forstater 2 , Matthew Brennaman 3 , Alfred Kleinhammes 2 , Thomas Meyer 3 , Yue Wu 2
1 Curriculum in Applied Sciences and Engineering, UNC-Chapel Hill, Chapel Hill, North Carolina, United States, 2 Physics & Astronomy, Univesity of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 3 Chemistry, Univesity of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractMultilayered titania nanotubes (TiNTs) are a novel material with potential applications in photocatalysis and solar energy. The unique nanotube morphology, characterized as delaminated anatase, gives rise to high surface areas that allow for high coverage by dye molecules with similar chemistry as observed in anatase nanocrystals. The nanotubes can be cut by a cold grinding process to form mono-dispersed short nanotubes. They form transparent films for photoelectrochemical characterizations and applications. In these applications, TiNT films coated with the phosponated dye complex Ru(bpy)2(4,4’-PO3H2bpy)2+ are being investigated for possible water splitting with visible light. The conduction band of the TiNTs is 300 meV higher than for anatase nanoparticles; but, as for anatase, the band structure can be manipulated by heat treatments of the nanotubes or Li+ ion intercalation, as shown by the present work. Photoinjection by the Ru dye complex into the Li+ loaded short TiNT films has been monitored through photoluminescence and time-resolved absorption spectroscopy.
Tuesday PM, December 01, 2009
Room 311 (Hynes)
2:30 PM - **Y5.1
Bridging the Gap in Electrocatalysis from Single-Crystal Surfaces to Nanoparticles.
Yang Shao-Horn 1
1 MSE/ME, MIT, Cambridge, Massachusetts, United States
Show AbstractDesign of highly active nanoscale catalysts for electro-oxidation of small organic molecules such as CO and methanol, and electro-reduction of oxygen is of great importance to the development of efficient fuel cells for energy storage of renewable energy. In this paper, we discuss two examples, where we verify whether fundamental knowledge of electrocatalytic activity established on single-crystal surfaces can be applicable to understand nanoparticle activity. First, we look at how the surface atomic structures of Pt nanoparticles influence CO and methanol electro-oxidation reaction, where we show increasing surface steps on Pt nanoparticles of ~2 nm can lead to enhanced intrinsic activity up to ~200% (current normalized to Pt surface area). Second, the surface electronic structures of Pt alloy nanoparticles as a result of near-surface compositions but not the surface atomic structures influence ORR activity. We discuss direct evidence of surface Pt sandwich-segregation structures of “Pt3Co” nanoparticles, which exhibit specific ORR activity ~4 times relative to Pt.
3:00 PM - Y5.2
Cross-sectional TEM Studies of Pt/γ-Al2O3 Model Catalyst System.
Zhongfan Zhang 1 , Long Li 1 , Malay Shah 1 , Lin-lin Wang 2 , Sergio Sanchez 3 , Qi Wang 4 , Duane Johnson 2 , Anatoly Frenkel 4 , Ralph Nuzzo 3 , Judith Yang 1
1 Mechanical Engineering and Materials Science Department, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Materials Science Department, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Department of Physics, Yeshiva University, New York, New York, United States
Show AbstractPlatinum nanoparticles (NPs) dispersed on γ-alumina substrate is one of the most widely used heterogeneous catalysis systems in commercial chemical and energy industrial applications, including petroleum refining and, hence, has been investigated extensively as a model catalyst system to elucidate structure-catalytic activity and selectivity relationships. γ-specific substrate characteristics contribute greatly both to geometry modifications of catalytic sites around the metal cation and to electron density changes around catalytic particles. Meanwhile, Pt particle size, shape, and oxygen defect density of support are crucial for catalyst performance. These results have a major impact on catalyst design and development. To elucidate the role of metal ions anchored in oxide supports, and the role of oxide structures in stabilizing the metal ions in their active state for catalyzing reactions, it is important to build up a model system to understand the structural relation of catalyst substrate. We develop new forms of model materials to establish with atomic precision the nature of the bonding that mediates metal support interactions in heterogeneous catalysis. Our specific research interest is to understand γ-Al2O3 support effects on the structure and chemistry of the Pt catalyst. In order to bridge the gap between the “real” and “simulated” worlds, we have produced thin films of single crystal γ-Al2O3 as model support material. We oxidize (110) NiAl alloys to grow γ- Al2O3 thin films, where oxidation temperature, air flow and oxygen partial pressure are systematically altered to determine optimal growth conditions. Atomic Force Microscopy, X-ray diffraction and Scanning Electron Microscopy are employed to characterize the γ-Al2O3 film morphology. Surface roughness is very important for the model system; we observed that morphology becomes flatter but more discontinuous as oxidation temperature is lowered from 950 to 600°C. Pt NPs will be deposited onto the oxides surface by Electron beam evaporation. Our interests will focus on the Pt/γ- Al2O3 interface by cross-sectional TEM in order to elucidate the support effects on catalyst particles.
3:15 PM - Y5.3
Novel Pathways to Hydrogen Dissociation and Diffusion on Pd Alloys.
Heather Tierney 1 , Ashleigh Baber 1 , John Kitchin 2 , E. Charles Sykes 1
1 , Tufts University, Medford, Massachusetts, United States, 2 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractDissociation of molecular hydrogen on the surfaces of Pd-based alloys is a key step in a number of energy-related technologies, including CO2 conversion and hydrogen separation. An understanding of the nature of H2-surface interactions, including molecular adsorption, dissociation and surface diffusion provides a basis for the development of next-generation energy technologies. In this low-temperature scanning tunneling microscopy study we have demonstrated that individual Pd atoms in an inert Cu matrix are active for the dissociation of hydrogen and subsequent spillover onto Cu sites. The atomic-scale composition of both Pd/Cu{111} and Pd/Au{111} near-surface alloys were elucidated and H uptake was quantified. Our results indicated that H spillover was facile on Pd/Cu at 400 K but that no H was found under the same H2 flux on a Pd/Au sample with identical atomic composition and geometry. Based on a simplistic model involving the adsorption energies of H on Pd{111}, Cu{111} and Au{111} it would appear that the barrier for H to migrate from Pd to Cu or Au is too high to occur at 400 K. DFT calculations provided insight into this unusual activity of Pd/Cu alloys for dissociation and uptake of H. The calculations revealed that the barrier for diffusion of H away from isolated Pd sites on Pd/Cu{111} alloys is lower than that of pure Pd{111}, but that this same diffusion barrier is insurmountable at 400 K on Pd/Au alloys. These results demonstrate the powerful influence an inert substrate has on the catalytic activity of Pd atoms supported in its surface.
3:30 PM - Y5.4
Engineering Pd Islands Supported on Au{111} for Hydrogen Dissociation and Storage.
Ashleigh Baber 1 , Heather Tierney 1 , Timothy Lawton 1 , E. Charles Sykes 1
1 Chemistry, Tufts University, Medford, Massachusetts, United States
Show AbstractThe use of bimetallic alloys in catalysis has enhanced the catalytic activity and selectivity of many reactions, leading to an increase of products and a reduction of side products and thermal waste. Palladium/gold (Pd/Au) bimetallic alloys have been used to catalyze important processes ranging from the synthesis of vinyl acetate and hydrogen peroxide to oxidative reactions of methanol, formic acid, and CO. Ultra-high vacuum scanning tunneling microscopy (UHV STM) is used not only to image bimetallic alloys, but also to spectroscopically probe the local electronic changes in both Pd and Au atoms when the two are alloyed. By elucidating the temperature dependence of the geometric structure of these surfaces, control can be gained over the position of the Pd atoms in the subsurface, surface, or overlayer islands. STM has been used to study hydrogen dissociation and spillover, which occurs easily on Pd/Cu{111}, yet not when small amounts of Pd are alloyed into the surface or subsurface layers of Au{111}. Pd/Au alloys may be prepared so that nanoparticle-sized Pd islands form on Au{111}. This structure provides an excellent test bed for the study of hydrogen interaction with Pd particles supported on Au{111}.
3:45 PM - Y5.5
Structural Investigation of Model Planar Perovskite-Supported Precious-Metal Catalysts.
Michael Katz 1 , Hong Liu 1 2 , Hung-Wen Jen 3 , Richard Soltis 3 , George Graham 1 , Xiaoqing Pan 1
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 College of Materials Science and Engineering, Sichuan University, Chengdu, Sichuan, China, 3 Chemical Engineering Department, Ford Motor Company, Dearborn, Michigan, United States
Show AbstractThe Daihatsu Intelligent Catalyst, for three-way automotive exhaust-gas catalysis, is based on the idea that precious-metal particles can alternately enter a perovskite support as cations under lean conditions and re-form as small metallic particles under rich conditions, thereby preventing particle coarsening and loss of catalytic activity over time. In order to investigate the underlying processes in detail, platinum, palladium, or rhodium was vacuum-deposited on various single-crystal perovskite support films, grown by pulsed laser deposition, and the resulting samples were treated under varying oxidative and reductive conditions. Transmission electron microscopy and related techniques were then utilized to observe precious-metal/perovskite interactions in these model planar catalyst systems and to characterize the resulting crystal structures. Preliminary results generally reveal dissolution and re-formation of metal particles. Many important features such as maintenance of long-term catalytic activity remain under investigation.
4:30 PM - Y5.6
Correlations Between Catalysis of Redox Reactions and Ionic Conductivity in Nanoparticles of Cerium Oxide Doped with Cu or Pd.
Hongying Liang 1 , Chih-Hui Lo 1 , Nan Yi 2 , Joan Raitano 1 , Rui Si 2 , Lihua Zhang 3 , Syed Khalid 4 , Maria Flytzani-Stephanopoulos 2 , Siu-Wai Chan 1
1 Dept. Applied Physics & Applied Math., Columbia University, New York, New York, United States, 2 Dept. Chemical & Biological Engineering, Tufts University, Medford, Massachusetts, United States, 3 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States, 4 National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractNanoparticles of Cu-CeO2 and Pd-CeO2 were prepared by aqueous co-precipitation for catalysis applications. The 8%Cu-CeO2 nanoparticles exhibited roughly similar levels of CO to CO2 conversion in catalysis of the water-gas shift reaction as samples with higher copper content. Impedance spectroscopy of Cu-CeO2 samples showed an increase in ionic conductivity and a decrease in activation energy for conduction with copper content and sintering temperature. However, the 1%Pd-CeO2 nanoparticles exhibited higher levels of conversion in steam reforming of methanol and methanol decomposition than higher Pd contents, and impedance spectroscopy of Pd-CeO2 showed a more complex relationship between Pd-dopant levels and ionic conductivity and activation energy. Select samples were characterized by high resolution transmission electron microscopy, x-ray diffraction, and x-ray absorption near edge spectroscopy. The implications of these results will be discussed as well as correlations between catalytic performance and ionic conductivity.
4:45 PM - Y5.7
Size-dependent Crystallinity of Nnoscale Heterogeneous Catalyst Pt/γ-Al2O3 Studied by HRTEM, EXAFS and ab initio Molecular Dynamics.
Long Li 1 , Lin-lin Wang 2 , Sergio Sanchez 3 , Joo Kang 3 , Qi Wang 4 , Zhongfan Zhang 1 , Anatoly Frenkel 4 , Duane Johnson 2 , Ralph Nuzzo 3 , Judith Yang 1
1 Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Department of Physics, Yeshiva University, New York, New York, United States
Show AbstractThe Pt nanoparticles (NPs) supported on γ-Al2O3 are well-known heterogeneous catalysts in the oxidation of hydrocarbon and CO, in fuel cells and oil-refining. Small metal NPs can exhibit reactivity and catalytic activity that are dramatically distinct, and sometimes completely opposite, from behaviors seen with larger particles, indicative of size-dependent structural changes. As an example, a novel phenomenon of negative thermal expansion (NTE) when the Pt particle sizes were ~1 nm was discovered recently [1]. To gain insights into NTE as well as explore other size-dependent structural anomalies, we characterized Pt NPs with a size range from sub- to 5 nm using high-resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine-structure spectroscopy (EXAFS) as well as modeled with ab initio molecular dynamics (MD) calculations. In order to enhance the HRTEM contrast of ~1 nm Pt NPs relative to the γ-Al2O3 support and C-film, focal-series reconstruction (FSR) was employed. The FSR HRTEM data revealed that Pt NPs <1 nm have a disordered structure while those >2.5 nm have an fcc structure. A transition range exists between 1.1 and 2.4 nm, in which more than 80% of the NPs appeared disordered and less than 20% ordered. The EXAFS measurements indicated an increasing distribution of disordered Pt-Pt bond lengths with decreasing nanoparticle sizes, which agrees with the general trend of size-dependent crystallinity. The MD simulations demonstrated that the ground-state structure of 1.1-nm Pt37/γ-Al2O3 (100) prefers a disordered structure, which is energetically more favorable than the ordered fcc structure by 1.53 eV (or 0.04 eV per Pt atom). The simulations support our experimental observation that the supported Pt NPs with diameters of ~ 1nm prefer a disordered structure.[1] J. H. Kang, L. D. Menard, R. G. Nuzzo, A. I. Frenkel, J. Am. Chem. Soc. 128 (37), (2006) 12068.
5:00 PM - Y5.8
Electrical Conductivity and Chemical Surface Exchange Studies in Nanoscale Titania Thin Films.
Changhyun Ko 1 , Annamalai Karthikeyan 1 , Shriram Ramanathan 1
1 SEAS, Harvard University, Cambridge, Massachusetts, United States
Show AbstractNonocrystalline Titania (TiO2) has been considered as one of promising candidates for various recently spotlighted applications such as photocatalysis, solar energy-driven water-splitting for hydrogen production, photovoltaics, chemical gas sensors, and self-cleaning coatings due to its photonic and electronic properties adequate for these applications as well as cheap price. Therefore, to improve the photoelectrochemical functionality of TiO2, the properties related with defect structure and kinetic parameters have been intensively researched. However, up to date, the surface kinetics of thin film TiO2 have been relatively less or not studied in comparison of bulk single crystalline TiO2 despite of technological advantages of thin film structures. In our work, the electric conductivity and chemical surface exchange coefficient were measured on ~500 nm-thick nanocrystalline TiO2 thin films (~13 nm grain size) grown on (0001) Al2O3 substrates by electrochemical impedance spectroscopy techniques and electrical conductivity relaxation measurements in our home-built furnace-type system equipped with four-probe measurement tools. In our films, n-type conductivity behavior was observed in the reduced atmosphere (PO2 < 10^-16 atm) at temperature higher than 700C and the measured conductivity values are quite well consistent with those obtained from single crystalline samples by other researchers. The activation energy for electric conduction is measured as ~1.45 eV and ~0.86~7 eV in air and reduced atmosphere regime (PO2 ~ 10^-17 atm) respectively. The surface kinetic constant was observed to be raised with increasing temperature. However, no significant influence from PO2 variation on surface kinetics was observed in the reduced environment regime (PO2 < 10-15 atm). The surface exchange coefficient was measured as 10^-4.9 cm/s and 10^-4.3 cm/s at 800C and 900C respectively.
5:15 PM - Y5.9
Enhanced Photocatalytic Disinfection of Escherichia Coli Bacteria by Silver and Nickel Co-modification of Nitrogen-Doped Titanium Oxide Nanoparticle Photocatalyst under Visible-Light Illumination.
Caixia Sun 1 , Qi Li 2 , Shian Gao 1 , Lihua Cao 1 , Jian Shang 1 2
1 Materials Center for Water Purification, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, Liaoning, China, 2 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractAnion-doped titanium oxide photocatalysts could be activated by visible light illumination, so that a greater portion of the solar spectrum may be utilized to provide energy input for photocatalytic disinfection system, which could eliminate the need of expensive and possibly hazard UV light source and reduce the operation cost. However, the photocatalytic efficiency of these anion-doped TiO2 photocatalysts under visible light illumination is relatively low due to the serious problem of massive charge carrier recombination from anion-doping. We recently reported that single-type transitional metal ion modification could largely improve the photocatalytic performance of TiON under visible light illumination due to the optoelectronic coupling between transitional metal ion addition and TiON semiconductor matrix, which promotes the charge carrier separation and subsequently decreases the electron-hole recombination. In this research, we furthered our work to a two-type transitional metal ion modification by synthesizing a nitrogen-doped titanium oxide nanoparticle photocatalyst with silver and nickel co-modification (TiON/Ag/Ni) and investigating its visible-light-induced photocatalytic disinfection effect on E. coli bacteria. Our work found that by introducing a small amount of second type transitional metal ion modification (nickel here in our current study with a Ni/Ti atomic ratio at only 0.3 %), the photodisinfection efficiency of the photocatalytic material system could be largely enhanced under visible light illumination. With careful optimization of the types and concentrations of transitional metal ion additions, multi-transitional metal ion modification could be a novel and effective approach to enhance the photocatalytic performance of anion-doped TiO2, and it has a great potential to provide photodegradation effect on organics, or disinfection effects on microorganism under visible light illumination for a wide range of environmental applications.
5:30 PM - Y5.10
Synthesis and Characterization of ZnO Supported Noble Metal Nanocatalysts for Energy Applications.
Jingyue (Jimmy) Liu 2 , Lawrence Allard 1
2 Center for Nanoscience and Dept. of Chemistry and Biochemistry, University of Missouri-St. Louis, St. Louis, Missouri, United States, 1 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractZnO supported noble metal catalysts have broad applications in energy production, conversion and utilization. For example, Pd supported on ZnO has shown promising properties as a catalyst for onboard steam reforming of methanol to produce hydrogen [1]. Fabricating nanocatalysts with atomic level control of the active sites requires atomic level understanding of the synthesis processes and how the synthesized nanostructures evolve during catalytic reactions. To better understand the atomic level processes of ZnO supported metal catalysts, we recently developed model nanocatalysts consisting of ZnO nanobelts and nanowires as support materials. The use of better-controlled nanostructures as catalyst supports not only provides a new route to synthesizing nanostructured heterogeneous catalysts but also greatly facilitating the atomic level understanding of the fabricated nanocatalysts. Catalyst precursor materials were produced by chemically deposit noble-metal containing salts onto the well-defined ZnO nanobelts or nanowires. There precursor materials were then reduced in an aberration-corrected (CEOS GmbH, Heidelberg, Ger) JEOL 2200FS microscope and by using a novel heating technology provided by Protochips Co. (Raleigh, NC) to study the formation processes of noble metal nanoparticles and their interactions with ZnO supports. The heating technology involves the use of unique MEMS-based heater chips that allow heating rates of 106 °C/sec, with extremely high specimen stability [2]. The atomic level processes of the formation of PdZn alloy nanoparticles, which have been considered to be responsible for the improved catalytic performance of Pd/ZnO catalysts [1], were investigated. The unusual interaction of Pd with ZnO and the newly created ZnO sites during the reduction processes may explain some of the recently reported performance of Pd/ZnO catalyst reduced at moderate to high temperatures [3-4]. Our in-situ electron microscopy data provided insights into the synthesis of ZnO supported noble metal nanocatalysts, the structural evolution of the metal nanoparticles and the nature of the final nanocatalysts [5].References1. Iwasa, N. et al. Appl. Catal. A 125, 145 (1995).2. Neyman, K. M. et al. Phys. Chem. Chem. Phys. 9, 3470 (2007).3. Conant, T. et al. J. Catal. 257, 64 (2008).4. Allard, L.F. et al. J. Micros. Res. & Tech. 72:208–215 (2009)5.This research at the Oak Ridge National Laboratory's High Temperature Materials Laboratory was sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program, and by the University of Missouri.
Symposium Organizers
Sheng Dai Oak Ridge National Laboratory
Harold H. Kung Northwestern University
Jun Liu Pacific Northwest National Laboratory
Chung-Yuan Mou National Taiwan University
Wednesday AM, December 02, 2009
Room 311 (Hynes)
9:30 AM - **Y6.1
Multifunctional Mesoporous Catalysts for Selective Conversions of Biological Feedstocks to Biodiesel and Ethanol.
Victor Lin 1 2
1 Department of Chemistry, Iowa State University, Ames, Iowa, United States, 2 , U.S. DOE Ames Laboratory, Ames, Iowa, United States
Show AbstractWe have developed a new synthetic strategy for preparing a series of multifunctionalized mesoporous metal oxide nanoparticle materials. This method allows us to tune the relative ratio of different functional groups and the resulting particle morphology of these nanomaterials. By utiliz-ing this method, we have developed a new cooperative catalytic system for biodiesel production from various biological feedstocks, including vegetable oils, animal fats, and algae. Also, we have synthesized a series of mesoporous carbon nanoparticle-supported metal catalysts for selective con-version of biomass-generated synthetic gas (CO and H2) to ethanol with high efficiency.
10:00 AM - Y6.2
HRTEM and DFT Studies OF MOS2/CO9S8 Interfaces: ``Understanding The Promotion Effect, Planar Interaction, And Bending Structures In Unsupported Catalysis Systems.”
Manuel Ramos 1 3 , Russell Chianelli 1 , Brenda Torres 1 , Domingo Ferrer 2
1 Materials Research Institute, UTEP, El Paso, Texas, United States, 3 Ciencias Basicas, Universidad Autonoma de Cd. Juarez, Cd. Juarez, Chihuahua, Mexico, 2 Microelectronics Research Center, University of Texas at Austin, Austin, Texas, United States
Show AbstractA study made using density functional theory based molecular modeling is presented here. This research work is made in order to understand promotion effect and structure/function on unsupported catalyst. Results indicated that d-electrons plays an important role promoting catalytical active sites at the edges of the so-called CoMoS phase (MoS2-Co9S8) unsupported catalytical particles. Information about how Co-Mo/S acted together on is been approached by Mössbauer spectroscopy, EXASF and other techniques. Using information obtained by TEM and HRTEM conducted DFT molecular modeling is presented for a MoS2/Co9S8 interface to explain planar contact between Co9S8 and MoS2 in an effort to explain observed structures in HRTEM using a FEI Tecnai instrument.
10:15 AM - Y6.3
A Comparative Study of Hydrogen Production from Methanol on Sub-nanometer Pd, Cu, and Co Clusters.
Faisal Mehmood 1 , Jeffrey Greeley 2 , Larry Curtiss 1 2
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractSupported subnanometer metal clusters are an emerging class of catalytic particles that, while not greatly studied in the past because of difficulties in stabilizing the clusters under realistic reaction conditions, have recently been shown to exhibit novel catalytic properties. In this contribution, we present a comparative density functional theory study of the methanol decomposition reaction on a spectrum of subnanometer clusters, including Pd4, Co4, and Cu4. The thermodynamics and kinetics of three decomposition routes involving C-O, C-H and O-H scission are investigated; activation energy barriers are determined with the nudged elastic band method. A detailed analysis of the PES for methanol decomposition shows C-O activation to be the least favorable step on all three metals. However, we find the activation barrier to be ~0.30 eV smaller on Co clusters. In addition, an analysis of all possible reaction paths reveals that activation energy barriers for most reactions on Co4 clusters are relatively low in comparison to Pd4 and Cu4 clusters, suggesting that the catalytic properties of Co4 will be significantly different from those of the other elements. Finally, we discuss the implications of a linear correlation that exists between the transition state and final state energies of all elementary reaction steps on the different metal clusters.
10:30 AM - Y6.4
Morphological Instability of Metallic Surfaces: Adsorbate Induced Nanoscale Faceting.
Govind Gupta 1 , Robert Baier 2 , Wenhua Chen 3 , Hao Wang 3 , Theodore Madey 3
1 Surface Physics & Nanostructures , National Physical Laboratory, New Delhi India, 2 , Helmholtz Zentrum Berlin für Materialien and Energien Abteilung Heterogene Materialsysteme, Glienicker Strabe 100, D-14109 Berlin Germany, 3 Department of Physics & Astronomy and Laboratory for Surface Modification, University of Rutgers, , Piscataway-08854, New Jersey, United States
Show AbstractHeterogeneous catalysis is a field of major interest in the surface science and development of new supported model catalysts with a narrow size distribution. The possibility to create narrow size distributions is to use the faceted surface structures as self assembled templates on which metal nanoclusters can grow. In the present study, new aspects of adsorbate induced faceting and nanoscale phenomena on adsorbate-covered metallic surfaces are studied on atomically-rough morphologically unstable metallic fcc (Rh) and hcp (Re) surfaces. Formation of oxygen induced faceting of atomically-rough Rh (210) surface has been studied and characterized by means of LEED, STM and AES. The LEED studies confirm the formation of three sided faceted (nanoscale pyramidal structure) Rh(210) surface when the oxygen covered Rh surface annealed to temperature higher than 550K. The facet orientations of the nanopyramid are characterized as two {731} face and a reconstructed (1 1 0) face. The excess oxygen overlayer can be removed from pyramidal faceted Rh(210) surface via catalytic reaction at low temperature using CO oxidation or H2 reaction while preserving the pyramidal structure. The average size of the nanopyramids is observed to be dependent on annealing temperature and vary from 12nm to 21nm. The atomically resolved STM images confirm the LEED observations and also revealed that (110) face of nanopyramids exhibits various reconstructions (1×n, n = 2-4) depending on oxygen coverage. Further, oxygen induced nanoscale faceted Re (12-31) surface has been formed which consist of nano-trenches (two sided ridges) with facets in (112-1) and (01-10) direction. These two- sided faceted Re (12-31) surface is used as a template to grow gold nanostructures. Under controlled growth conditions, the gold induced nanostructures are formed on oxygen induced nano-trenched Re (12-31) surface. It is observed that gold grows in the form of islands on the faceted rhenium substrate i.e. at lower coverages (≥0.8ML), it forms 2D islands whereby for higher coverages 3D islands are formed on top of the nano-ridges. The surfaces morphology of the gold covered faceted Re surface changes drastically on annealing, for the temperature >870 K, gold atoms wet the rhenium template while annealing to higher temperature (~970K) led to the development of a three sided nanopyramids. On further annealing to higher temperatures (>1100K) cause the complete destruction of the faceted structure. LEED and STM studies revealed that the gold induced three sided nanopyramids consists of two faces of original two sided ridges with(11-21), (01-10) orientation and an additional facet in (12-32) direction. The high resolution STM images revealed that the (12-32) facet of the nanopyramid is fully decorated with single atomic zigzag gold nanochain. These faceted surfaces can be potential template for heterogeneous catalysis and development of new supported model catalysts with a narrow size distribution.
10:45 AM - Y6.5
Understanding Oxygen Reduction Reaction Process on Fe-Phthalocyanines (FePc) and Co-Phthalocyanines (CoPc) in Alkaline Solution from Density Functional Theory Calculations.
Guofeng Wang 1 2
1 Department of Mechanical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana, United States, 2 Richard G. Lugar Center for Renewable Energy, Indiana University Purdue University Indianapolis, Indianapolis, Indiana, United States
Show AbstractCatalytic FePc and CoPc molecules have been studied extensively as catalysts for oxygen reduction reactions (ORR), particularly for fuel cell application in alkaline solution. Despite much progress, reaction mechanisms of ORR on the FePc or CoPc catalysts at a molecular level have not been well understood yet. By applying density function theory (DFT) calculations to studying the adsorption process of reactant, intermediate, and product molecules on the FePc or the CoPc surface, we achieved a fundamental understanding of the ORR mechanisms catalyzed by the FePc and CoPc. Specifically, we determined the fully optimized structure and energy for O2, H2O, OH, HOOH, and H2OO molecules adsorbed on the surface of the FePc and CoPc molecules using DFT method. By relating our theoretical results with published experimental observations, we concluded for ORR on FePc and CoPc that (1) O2 adsorption process is the limiting step affecting the kinetics of ORR, (2) OH adsorption process determines the durability of FePc and CoPc, and (3) H2O2 adsorption process distinguishes the four-electron and two-electron routes of ORR. Our study provides new guiding principles on how to tailor the chemistry to attain better macrocycle molecule catalysts for solid electrolyte alkaline fuel cells.
11:30 AM - **Y6.6
Roles of Surface Junctions and Co-catalysts Played in Photocatalytic Hydrogen Production.
Can Li 1
1 Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian China
Show AbstractThis lecture presents recent progress made in photocatalytic hydrogen production utilizing solar energy and fundamental understanding of photocatalysis and photochemical reactions on semiconductor catalysts. The concerns about the depletion of fossil fuel reserves and the pollution caused by continuously increasing energy demands make hydrogen an attractive energy source. Solar energy is the primary source for clean and renewable energy alternative. Photocatalytic hydrogen production using solar energy is a promising process for renewable energy production, considered as an efficient strategy to eventually realize hydrogen economy. Semiconductor materials are believed to be the most promising components for photocatalysts, so the discovery and synthesis of novel semiconductor materials are crucial for the development of advanced photocatalysts. To convert more solar energy into chemical energy, much attention has been paid to reducing charge recombination and improving solar energy conversion efficiency. Our recent results demonstrate that the formation of surface phase junction and hetero-junction on semiconductor catalysts can significantly enhance the activity in photocatalytic hydrogen production. By mimicking the photosynthesis, loading spatially separated dual cocatalysts for oxidation and reduction on semiconductor nanoparticles can obviously avoid the charge recombination and consequently increase the photocatalytic activity. These findings provide a strategy to develop highly active photocatalysts for hydrogen production utilizing solar energy.
12:00 PM - Y6.7
Superior Electrocatalytic Activity of Pt3Co Nanocubes towards Methanol Oxidation Reaction.
Jun Zhang 1 , Hongzhou Yang 2 , In-Tae Bae 3 , Dae Young Jung 3 , Shouzhong Zou 2 , Jiye Fang 1
1 Chemistry, State University of New York at Binghamton, Binghamton, New York, United States, 2 Chemistry and Biochemistry, Miami University, Oxford, Ohio, United States, 3 Small Scale Systems Integration and Packaging Center, State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractWe report a novel, reliable and high-yield synthesis strategy developed using a high-temperature organic solution approach for preparing monodisperse Pt3Co nanocubes. TEM and SEM-based characterization shows that the as-prepared alloy particles are single crystalline and cubic in shape with a monodistribution of size. X-ray diffraction and HRTEM investigation confirms the presence of {100} faces among these nanocubes. Using energy dispersive X-ray spectroscopic (EDS) and inductively coupled plasma mass spectrometric (ICP-MS) techniques, the composition was determined as Pt3Co. The electrocatalytic activity of these Pt3Co nanocubes towards methanol oxidation reaction is also evaluated in comparison with similarly sized irregular shaped Pt3Co and pure Pt nanocubes, respectively. The results show that these monodisperse Pt3Co nanocubes fabricated through a relatively facile wet-chemical approach demonstrate a superior electrocatalytic activity towards methanol oxidation, and they could potentially be used as efficient anode electro-catalysts in fuel cells.
12:15 PM - Y6.8
Model Based Prediction of a Ni/Pt Bimetallic Catalyst for H2 Production from NH3 Decomposition.
Danielle Hansgen 1 , Jingguang Chen 1 , Dionisios Vlachos 1
1 Chemical Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractThe ammonia decomposition reaction has recently received increased attention due to the possibility of ammonia being used as a hydrogen storage medium in a possible hydrogen economy. We have explored this decomposition reaction through multiscale microkinetic modeling for a number of transition metal catalysts, including Cu, Pt, Ir, Ru, Pd, Rh, Co, Ni, Fe, W, and Mo, to better understand the reaction mechanism. An understanding of the reaction mechanism and electronic properties of these metals has given insight into how to tailor catalysts to improve catalytic activity for this reaction.The mechanism consists of 12 elementary reaction steps and 5 surface species, namely N, H, NH, NH2, and NH3. For many of the metals, a large portion of the surface is covered by adsorbates. For these metals, repulsive adsorbate-adsorbate interactions were expected to change the binding energies of the surface species, thereby changing the elementary reaction activation barriers and modifying the catalytic activity [1]. Coverage dependant atomic heats of chemisorption were calculated through DFT using the Vienna Ab-initio Simulation Package (VASP) for the various transition metal catalysts. Coverage dependant molecular binding energies were calculated using a method based on scaling relationships published by Abild-Pederson et al. [2] and activation barriers were calculated through the bond-order conservation (BOC) method [3]. Inclusion of the interaction parameters to the models resulted in reduced nitrogen coverages and a peak shift in the volcano curve. The conversions were plotted against the characteristic nitrogen heat of chemisorption for each metal, which was found to be an adequate descriptor for this reaction. The volcano curve of the conversions calculated through the microkinetic models are in good agreement with experimental data of single metal catalysts by Ganley and coworkers [4]. The maximum activity was found at a nitrogen heat of chemisorption of approximately 130 kcal/mol.A DFT study of nitrogen binding energies on Pt-3d bimetallic surfaces showed a binding energy of 131 kcal/mol on the Ni-Pt-Pt surface, indicating that it could be a potentially active catalyst; therefore surface science experiments were performed to assess the microkinetic model and DFT results. The Ni-Pt-Pt surface was found to be more active at decomposing ammonia at low temperatures and desorbed nitrogen at lower temperatures than a Ru(0001) surface, currently the most active single metal catalyst.1. Mhadeshwar, A.B., Kitchin, J.R., Barteau, M.A., and Vlachos, D.G., Catal. Lett. 96, 13 (2004). 2. Abild-Pedersen, F., Greeley, J., Studt, F., Rossmeisl, J., Munter, T.R., Moses, P.G., Skulason, E., Bligaard, T., and Norskov, J.K., Phys. Rev. Lett. 99(2007). 3. Shustorovich, E., and Sellers, H., Surf. Sci. Rep. 31, 5 (1998). 4. Ganley, J.C., Thomas, F.S., Seebauer, E.G., and Masel, R.I., Catal. Lett. 96, 117 (2004).
12:30 PM - Y6.9
Anodic Growth of self-organized TiO2-nanotubes and Catalytic Properties.
Robert Hahn 1 , Indhumati Paramasivam 1 , Felix Schmidt-Stein 1 , Patrik Schmuki 1
1 University Erlangen, Department Material Science, Institute of Surface Science, Erlangen Germany
Show AbstractSelf organized nanotubular structures of transition metal oxides grown on their metallic substrates, especially titanium [1], have attracted great scientific and technological interest due to the possibility to exploit their functional properties (such in photo-catalysis, solar energy conversion and biotechnology) in a nanotubular morphology. In the first part of the work we report on the growth of anodic TiO2 nanotubes by a simple one-step electrochemical treatment of Ti in fluoride containing electrolyte (for an overview see [2,3]) and the optimization of the nanotube morphology for catalytic applications.The second part of the presentation will demonstrate that the catalytic properties of these TiO2 nanotubes can be significantly modified by loading with suitable nanoparticles (Ag, Au, Fe3O4) [4], filling with Zeolite [5] or C-doping [6,7] for very high electronic conductivity.Literature:[1] V. Zwilling, M. Aucouturier, E. Darque-Ceretti, Electrochim. Acta, 45, 921 (1999).[2] J.M Macak et al., Curr Opin Solid State Mater Sci 11 (2007).[3] A. Ghicov, P. Schmuki, Chem. Commun. Andrei Ghicov and Patrik Schmuki, Chem. Commun., 2791, doi:10.1039/b822726h (2009)[4] I. Paramasivam, J.M. Macak, P. Schmuki Electrochemistry Communications 10 (2008) 71–75[5] I. Paramasivam, A. Avhale, A. Inayat, A. Boesmann, P Schmuki and W Schwieger Nanotechnology 20 (2009) 225607 (5pp)[6] R. Hahn, A. Ghicov, J. Salonen, V. Lehto, P. Schmuki, Nanotechnology, 18, 105604 (2007).[7] R. Hahn et al. (2009) submitted.
12:45 PM - Y6.10
Hydrogen Adsorption on Pd Decorated ZnO Nanopowders.
Eduardo Cruz-Silva 1 , Paige Landry 2 , Andrew Lupini 1 , Bobby Sumpter 1 , John Larese 1 2
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of Tennessee, Knoxville, Tennessee, United States
Show AbstractMolecular hydrogen adsorption on Zinc Oxide nanopowders synthesized using a novel process and subsequently decorated with Pd nanoclusters has been investigated using thermodynamic, electron microscopy and inelastic neutron scattering (INS) methods. These measurements suggest that molecular hydrogen is adsorbed preferentially on the surface of Pd and does not form a metal hydride phase, but apparently physisorbs. The INS measurements suggest that the hydrogen bond length increases by about 6%.To probe these findings, the adsorption dynamics of H2 in Pd and ZnO is investigated by ab initio and semiempirical calculations. Modeling results confirm that hydrogen tends to form hydrides as the first adsorption layer in both materials. However, semiempirical calculations of the combined system show that charge transfer effects cause hydrogen to stretch by about 15% and adsorb in the surface of the Pd cluster, in accord with the experimental results. This result suggests that the combined system may yield promising information for applications in hydrogen storage and catalysis. This work was supported by U.S. DOE Basic Energy Science, with contract no. DE-AC05-00OR22725 with ORNL.
Y7
Session Chairs
Maria Flytzani-Stephanopolous
Harold Kung
Wednesday PM, December 02, 2009
Room 311 (Hynes)
2:30 PM - **Y7.1
Designing Electrocatalytic Nanoarchitectures in 3D.
Debra Rolison 1 , Jeffrey Long 1 , Jean Marie Wallace 2 , Christopher Chervin 2 , Justin Lytle 3 , Jennifer Dysart 1
1 Surface Chemistry, U.S. Naval Research Laboratory, Washington, District of Columbia, United States, 2 , Nova Research, Inc., Alexandria, Virginia, United States, 3 Chemistry, Pacific Lutheran University, Tacoma, Washington, United States
Show AbstractThe support–catalytic metal–molecule intersection typical of many heterogeneous catalytic and electrocatalytic reactions has always exemplified nanoscience en route to important technological and societal processes that produce energy or chemicals. Rethinking this three-phase intersection can now be done in light of architectural nanoscience, i.e., the design and fabrication of three-dimensional (3-D) multifunctional architectures from the appropriate nanoscale building blocks [1], including the use of “nothing” (void space) and deliberate disorder as design components [2]. Improved performance arises when the multifunctionality inherent to catalytic processes, including molecular transport of reactants and products, is structured within such architectures [3]. Our nanoarchitecture of choice for electrocatalysis is sol–gel-derived aerogels and nanofoams (underdense, innately nanoscale, ultraporous materials) in which the desired catalytic nanoparticle is introduced by modifying fiber paper-supported polymer gels with thiophenyl moieties to produce, upon pyrolysis [4], highly conductive carbon nanofoams containing an anchoring site for electrocatalytic metal nanoparticles. By preparing the foams within the voids of carbon fiber paper, device-ready electrodes are obtained that provide through-connected flow fields for reactant and product transport to surface-anchored nanoscale catalysts such as Au, Pt, Pd, or Ag. This core structure provides an electrocatalytic reactor that can be segued as desired for fuel cells, semi-fuel cells, air cathodes, or electrosynthesis.[1] D.R. Rolison, J.W. Long, J.C. Lytle, A.E. Fischer, C.P. Rhodes, T.M. McEvoy, M.E. Bourg, A.M. Lubers, Chem. Soc. Rev. 2009, 38, 226.[2] D.R. Rolison, Science 2003, 299, 1698.[3] J.W. Long, D.R. Rolison, Acc. Chem. Res. 2007, 40, 854.[4] W.S. Baker, J.W. Long, R.M. Stroud, D.R. Rolison, J. Non-Cryst. Solids 2004, 350, 80.
3:00 PM - Y7.2
Synthesis of High Surface Area Materials for Solid Oxide Fuel Cells.
Robin Chao 1 , John Kitchin 2 , Paul Salvador 1 , Christopher Matranga 3
1 Material Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 3 , National Energy Technology Laboratory, Pittsburgh, Pennsylvania, United States
Show AbstractThe efficiency of solid oxide fuel cells (SOFCs) is limited by cathode polarizations; therefore, it is essential to understand the factors that influence the oxygen reduction reaction at the surface of cathode materials. Many tools useful for surface chemical measurements, such as IR spectroscopy, require very high specific surface area powders to generate a usable signal. Conventional methods used to synthesize perovskites, materials commonly used for SOFC cathodes, are known for producing particles of limited specific surface areas (4m2/g ~ 30m2/g). Two approaches to the production of extremely high surface area (>100m2/g) powders were explored in this work: evaporated-induced self-assembly (EISA) and SBA-15 hard templating. In EISA, a mesoporous soft template is first formed with surfactants, is then backfilled with metal precursors, and is finally calcined to produce mesoporous oxide powders with high surface areas. In the SBA-15 route, an orderly mesoporous SBA-15 sieve is used as the hard templating agent, it is backfilled with nitrate precursors, and oxide powders again form on calcination, after which the hard silica template removal. The powders made were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and gas adsorption analysis, such as BET and BJH methods. By controlling the synthesis parameters and the nature of the surfactants in EISA, pure perovskites (such as LaMnO3 and La1-xSrxMnO3) were produced with specific surface areas of 40m2/g~50m2/g, higher than powders prepared from conventional methods. It was observed that the surface area increases from 4m2/g to 50m2/g as the precursor/surfactant ratio increases. Results also suggest that powders produced with CTAB surfactants have higher surface areas than the ones produced with P123 surfactants. The LSM powders prepared using the SBA-15 hard template approach had extremely high surface areas, >100m2/g. Parameters that lead to high surface area powders will be dicussed. Characterization of the high surface area perovskite powders were done using temperature programmed desorption (TPD) and thermogravimetric analysis (TGA); results will be correlated to oxygen exchange mechanisms.
3:15 PM - Y7.3
Understanding the Role of Ni-YSZ During Reducing Conditions.
L. Saraf 1 , D. Baer 1 , Z. Zhu 1 , A. Lea 1 , J. Strohm 2 , C. Wang 1 , D. King 2
1 Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington, United States, 2 Energy and Environmental Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractFundamental understanding of oxygen transport behavior and catalytic reactions in solid oxide fuel cells (SOFC) has been of great interest to research community for years due to the need for development in efficient alternative energy technology. Recent developments in new spectroscopic and microscopic techniques have made it possible to investigate catalytic materials related to SOFC in greater details. Large scale efforts throughout the research community are underway to enable an effective oxygen ion transport, hydrocarbon dissociation in SOFCs at intermediate operating temperatures. Ni-YSZ (nickel yttria-stabilized zirconia) is being developed as an anode material for use in SOFC fuel cells where the choice of Ni comes from its moderate cost compared with precious metals and high catalytic activity to steam reform CH4 to generate hydrogen, which is subsequently electrochemically converted as a fuel. By using ToF-SIMS, EDS as well as AES mapping along with FIB sectioning on Ni-YSZ samples prepared after hydrogen reduction followed by prolonged methane reforming, we investigate the reduction process in Ni-YSZ along with mobility of Ni during these processes. The data is discussed in the context of Ni exsolution process along with interfacial phase segregation reactions and its impact on long term SOFC operation efficiency and stability.
3:30 PM - Y7.4
Surface Reconstruction Studies of SOFC Cathodes using a Combination of Synchrotron Radiation Techniques and Electrochemical Measurements.
Lincoln Miara 1 , Jacob Davis 1 2 , Laxmikant Saraf 3 , Tiffany Kaspar 3 , Uday Pal 1 , Soumendra Basu 1 , Karl Ludwig 2 , Srikanth Gopalan 1
1 Division of Materials Science, Department of Mechanical Engineering, Boston University, Brookline, Massachusetts, United States, 2 Department of Physics, Boston University, Boston, Massachusetts, United States, 3 WR Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractEpitaxial crystals of Strontium doped Lanthanum Manganite (LSM) were grown by Pulsed Laser Deposition (PLD). LSM is used as a cathode material in Solid Oxide Fuel Cells (SOFCs) due to its stability at high temperature, good compatibility with the YSZ electrolyte, high electronic conductivity and its high catalytic activity for the reduction of oxygen. In the commercialization of SOFCs a great challenge is to lower the operating temperature from 1000 degrees Celsius to between 600 and 700 degrees. At these lower temperatures the cathodic reduction of oxygen becomes the limiting step of SOFC performance. However, the role of the cathode surface in the oxygen reduction and incorporation reaction is poorly understood especially at these low temperatures. Thus, in this study we investigated the two phase boundary between the epitaxially grown cathode and the surrounding gas phase at different partial pressures of oxygen in the temperature range of 600-750 degrees Celsius. 25nm thick samples of LSM on Lanthanum Aluminate (LAO) were grown by PLD. These samples were then investigated on at the National Synchrotron Light Source (NSLS)at Brookhaven National Laboratory (BNL). The aim of the study was to correlate structural changes to changes in electronic properties of the cathode. To accomplish these tasks we have correlated equilibrium EXAFS, XANES, XPS, and XAS results to electrical conductivity data. Also we have used time resolved EXAFS on the Sr, La, and Mn edges, as well as the Electrical Conductivity Relaxation (ECR) measurements to correlate the surface exchange coefficient to cation surface segregation. Future work will involve examining the effect of a potential bias on structural and electrical characteristics, as well as the investigation of a cathode that is a mixed ionic and electronic conductor.
3:45 PM - Y7.5
Strain-enhanced Oxygen Reduction in Epitaxial (La,Sr)CoO3 Films for SOFCs.
SungJin Ahn 1 , Gerardo Jose la O' 1 , Ethan Crumlin 1 , Yuki Orikasa 1 , Michael Biegalski 2 , Hans Christen 2 , Yang Shao-Horn 1
1 Electrochemical Energy Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractReduction of operating temperatures is of vital importance to shorten start-up time and reduce degradation of components in solid oxide fuel cells (SOFCs). Decreasing the operating temperature, however, reduces the SOFC conversion efficiency since the kinetics of electrochemical reactions, especially the oxygen reduction reaction (ORR), are thermally activated. The lack of fundamental understanding of the ORR mechanism at the molecular level limits the design of new cathode materials with enhanced activity at intermediate temperatures. In this study, we show that strains in epitaxial oxide thin films can enhance the ORR activity. This enhancement was demonstrated using (001)-oriented La0.8Sr0.2CoO3-δ (LSC) films. LSC films were epitaxially grown on 9.5 mol% Y2O3-stabilized ZrO2 (YSZ) (001) single-crystals, with an epitaxial buffer layer of 20 mol% Gd-doped CeO2 (GDC) using pulsed-laser deposition. The thicknesses of the LSC films were 45 nm and 135 nm, each exhibiting different strains. Stoichiometric surface and film compositions of the LSC films were verified using Rutherford backscattering spectroscopy and Auger electron spectroscopy. Crystallinity, epitaxial relationships, and strains of LSC/GDC/YSZ (001) films were analyzed using 4-circle X-ray diffraction. ORR activity of the films was investigated using electrochemical impedance spectroscopy at 520°C under varying oxygen partial pressures between 10-4 atm to 1 atm. It is hypothesized that the enhanced surface exchange coefficient of the 45 nm LSC (001) film can be attributed to a larger tensile strain than in the thicker layer, leading to a higher oxygen vacancy concentration.
4:30 PM - Y7.6
Halogenated Polypyrroles as Catalysts for Proton Exchange Membrane Fuel Cells.
Jeremy Pietron 1 , Justin Biffinger 2 , Syed Qadri 3
1 Surface Chemistry Branch, Code 6170, Naval Research Laboratory, Washington, District of Columbia, United States, 2 Chemical Dynamics and Diagnostics Branch, Code 6110, Naval Research Laboratory, Washington, District of Columbia, United States, 3 Materials and Sensors Branch, Code 6360, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractMetallated polypyrroles have recently been shown to be moderately active catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC), and thus as a potential candidates for replacement of the precious metal catalysts therein (e.g.: R. Bashyam, P. Zelanay Nature 443 (2006) 63–66; A. L. M. Reddy, N. Rajalakshmi, S. Ramamprabhu Carbon 46 (2008) 2–11; M. Yuasa, A. Yamaguchi, H. Itsuki, K. Tanaka, M. Yamamoto, K. Oyaizu Chem. Mater. 17 (2005) 4278–4281). We have synthesized perfluorinated pyrrole using a method developed by DiMagno and co-workers (E. K. Woller, V. V. Smirnov, and S. G. DiMagno J. Org. Chem 13 (1998) 5706-5707), with the goal of developing perfluorinated polypyrrole (F–ppyr) electrocatalysts that perform the ORR at considerably lower overpotentials than existing Co–ppyr/C catalysts. Fluorine substitution on the β-position of pyrrole withdraws electron density from coordinated metal centers generating an anodic shift in the redox potential of the metal. Adding halogen groups to pyrrole provides a means of tuning the electronic state of electrocatalysts derived from them and thus the overpotentials of the reactions they catalyze. Synthesis of perfluorinated pyrrole and polypyrrole will be described, as well as the deposition of F–ppyr on carbon, and the metallation of the composite catalyst. The activity of the F-ppyr composite catalyst for the ORR will be compared to that of Co–ppyr/C. Additionally, initial attempts at application of F-ppyr composite catalysts as anode catalysts for the oxidation of alternative fuels such as methanol will be described.
4:45 PM - Y7.7
Tungsten Monocarbide (WC) and Pt-Modified WC as Hydrogen Evolution Catalysts.
Daniel Esposito 1 2 3 , Irene Hsu 1 2 , Kevin Dobson 3 , Brian McCandless 3 , Robert Birkmire 3 , Jingguang Chen 1 2
1 Chemical Engineering, University of Delaware, Newark, Delaware, United States, 2 Center for Catalytic Science and Technology, University of Delaware, Newark, Delaware, United States, 3 Institute of Energy Conversion, University of Delaware, Newark, Delaware, United States
Show AbstractFor the electrolysis of water in acidic solutions, the best hydrogen evolution reaction (HER) catalysts are precious metals such as platinum (Pt), but their prohibitively high costs are major hurdles for the widespread production of hydrogen by this means. One approach for overcoming this challenge is to disperse small amounts of the active precious metal on a low-cost, stable support or co-catalyst. In this work, we investigate the performance of tungsten monocarbide (WC), modified by sub-monolayer to multilayer amounts of Pt, as HER catalysts. WC is an attractive material for this purpose, as it shows Pt-like catalytic properties [1], displays good stability in acidic solutions [2], and has demonstrated synergistic effects when combined with Pt as an electrocatalyst [3]. One complication in using tungsten carbide as an electrocatalyst is the tendency of forming a thin layer of carbonaceous carbon on its surface during synthesis [4]. Carbon is commonly used as a stable catalyst support material, but it is also known to have detrimental effects on the Pt-like properties of WC [4]. In this work, we investigate the role of surface carbon on the stability of phase pure WC and Pt-modified WC in acidic solutions, as well as the activity of both towards the HER. These studies have been conducted using phase-pure WC thin film electrodes deposited on polycrystalline tungsten foils. The phase purity of WC films has been verified using X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) has been used to show that the amount of surface carbon on the WC film surface may be altered by modification of gas flow during synthesis. The stability and activity of the WC electrode in a 0.1 M H2SO4 solution has been investigated using linear sweep voltammetry (LSV) and cyclic voltammetry (CV). Preliminary CV measurements indicate that carbonaceous carbon increases the activity of WC towards the HER, but also increases its susceptibility to corrosion. Pt-modification of the WC surface is achieved by physical vapor deposition of Pt, and the coverage of Pt is characterized by XPS and SEM. LSV measurements show that HER activity on WC approaches that of pure Pt upon modification with Pt, and post-electrochemistry XPS measurements indicate no loss of Pt from the carbon-free WC surface. Current work is focused on investigating the effect of different coverages of Pt on the HER activity on carbon-free and carbon-containing WC surfaces.References[1] R.B. Levy, and M. Boudart, Science, 181 (1973) 547.[2] M.B. Zellner and J.G. Chen, Catal. Today, 99 (2005) 299-307.[3] E.C. Weigert, A.L. Stottlemyer, M.B. Zellner and J.G. Chen, J. Phys. Chem. C, 111 (2007) 14617.[4] P.N. Ross and P. Stonehart, J. Catal., 39 (1975) 298.
5:00 PM - Y7.8
A Nanostructured ZnO-carbon Composite as Materials Platform for Cataylsis and Sensing.
Joerg Schneider 1 , Jayaprakash Khanderi 1 , Aleksander Gurlo 1 , Rudolf Hoffmann 1
1 Department of Chemistry, TU Darmstadt, Darmstadt Germany
Show AbstractCarbon nanotubes (CNTs) and ZnO nanostructures have each found widespread interest in the areas of catalysis as well as physical and chemical sensing. Therefore an assembly of ZnO nanoparticles onto the surface of CNTs may create interesting synergistic effects which are different from the single components alone. Using a single source approach we have synthesized nanoscale ZnO at moderate temperatures and decorated these nanoparticles on the outside of multi walled CNTs. The degree and particle agglomeration of ZnO decoration can be steered by adjusting the molecular precursor concentration. The ZnO/CNT material is a highly selective sensor for very low (20, 50 and 200 ppm) CO concentrations. By further grafting Au nanoparticles onto the surface of this ZnO/CNT composite a ternary catalytic active material is formed. The interface of the nanoparticles is studied by various techniques.
5:15 PM - Y7.9
Synergetic Interplay of Electronic and Geometric Effects in Enhanced H - Pd Nanoparticle Interaction.
Manika Khanuja 1 , Bodh Mehta 1 , Pawan Kulriya 2 , Devesh Avasthi 2
1 Physics, Indian Institute of Technology Delhi, New Delhi India, 2 , Inter-University Accelerator Centre, Aruna Asif Ali Road, New Delhi-110067, Delhi, India
Show AbstractPd-H interaction is probably the most important solid surface - gas molecule interaction due to its direct relevance in hydrogen technology and also due to the scientifically interesting physical, chemical and electronic processes accompanying the interaction. In the present study, the effect of nanoparticle character on the Pd-H interaction has been studied by investigating hydrogen induced changes in the structural and electrical properties of Pd nanoparticle and thin film samples. Our results show that the change over from the normally observed slow saturation response in Pd thin films or bulk samples to a pulsed response in Pd nanoparticles is due to increased physical adsorption and the presence of interparticle gaps in nanoparticle layers. In pulsed response, electrical resistance first increases due to electronic effect followed by a sudden decrease due to geometric effect. Electronic effect is due to hydrogen acting as scattering centres due to which electrical resistance increases and geometric effect arises due to lattice expansion during PdH formation due to which electrical resistance decreases. For H2 concentration ≥ 2.5% pulsed response has been observed whereas for H2 concentration ≤ 2.0%, a saturated response has been observed at room temperature. The threshold concentration at which the changeover (from slow saturation to pulsed response) takes place is observed to be a sensitive function of measurement temperature. In-situ X-ray diffraction measurements show a marked difference in the hydrogen induced structural changes (lattice expansion and crystallinity degradation) in Pd nanoparticles in comparison to thin film samples, especially at low H concentrations and low measurement temperature. Single β phase is observed in case hydrogen loaded Pd nanoparticle samples in a larger concentration and temperature range in comparison to mixture of α and β phases in thin film samples. The crystallite interlocking, stresses due to difference in the lattice constant of two PdH phases retards hydrogenation process in Pd thin film samples. These results will be explained in terms of the basic processes of physical adsorption, chemisorption and diffusion and their dependence on temperature and pressure. This study shows that by varying the relative magnitude and response time of geometric and electronic changes by controlling nanoparticle size and interparticle gaps, a hydrogen sensor having the fast response of the electronic effect, large sensitivity of the geometric effects and capable of functioning at low temperature (- 100°C) can be fabricated.
5:30 PM - Y7.10
Influence of Catalyst on Nanostructured Metal Oxide Gas Sensor Performance.
George Whitfield 1 , Erin Kyle 1 , Sooh-Yun Kim 2 , Il-Doo Kim 2 , Harry Tuller 1
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Center for Energy Materials Reseach, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractNanostructured chemical sensors based on semiconducting metal oxides (SMOs) exhibit high sensitivity to oxidizing and reducing gases (e,g, NO2 and CO) when heated to temperatures sufficiently high to activate chemisorption/desorption processes. Such sensors often suffer from poor selectivity due to activation of competing reactions from multiple interfering gases in the ambient. Noble metals (e.g. Pt, Ru, Au) are known to have a high level of catalytic activity in the presence of such gases, especially when fabricated in the form of nanoparticles. In prior studies, metal nanoparticles were combined with SMOs to form chemical sensors with reduced operating temperatures and improved selectivity. [1,2] However, the mechanisms that underlie the observed improvements in performance are not yet well understood. In the present work, the authors investigate these interactions using SMO based chemical sensors formed by microsphere templating that supports the film above the substrate and enhances interaction with the gases. [3] The nature and dispersal of the noble metal nanoparticles onto the SMO layers is systematically varied, and the resultant impact on device sensitivity, selectivity and response time is investigated with the results modeled to isolate contributions from metal-gas, SMO-gas, and metal-SMO interactions.[1] D.S. Vlachos, C.A. Papadopoulos, J.N. Avaritsiotis, “Characterization of the catalyst-semiconductor interaction mechanism in metal-oxide gas sensors.” Sensors and Actuators B 44 (1997) 458-461.[2] J.C. Kim, H.K. Jun, J.S. Huh, D.D. Lee, “Tin oxide-based methane gas sensor promoted by alumina-supported Pd catalyst.” Sensors and Actuators B 45 (1997) 271-277.[3] I.D. Kim, A. Rothschild, T. Hyodo, H.L. Tuller, “Microsphere Templating as Means of Enhancing Surface Activity and Gas Sensitivity of CaCu3Ti4O12 Thin Films.” Nano Letters 6 (2006) 193-198.
5:45 PM - Y7.11
A First-Principles Study of O2 Reduction by Lithium on Different Catalytic Materials.
Ye Xu 1 , William Shelton 2
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractAn important goal of current energy research is to design a battery system that can replace gasoline as the sole power source for automobiles. The state-of-the-art lithium-ion batteries, which are based on Li-intercolated cathode materials, do not have the required energy density. Li–O2 has one of the largest theoretical energy densities of any practical electrochemical couples at over 11 kWh/kg, which makes Li-air batteries a potential solution. The lack of rechargeability of prototype Li-O2 cells, however, is a major obstacle for making a practical transportation battery. To begin to address this challenge, a detailed understanding of Li-oxygen surface chemistry is needed. Toward that end, we have used first-principles density functional theory based methods to investigate the reduction of O2 by Li on the Au(111), graphite(001), and graphene surfaces, which are representative of the types of material used to construct the cathodes of prototype Li-air batteries. The adsorption energetics of Li-oxygen species turns out to be distinctly different on the metal vs. carbon, which suggests that the reversibility of O2 reduction by Li is a material-dependent phenomenon.
Y8: Poster Session
Session Chairs
Thursday AM, December 03, 2009
Exhibit Hall D (Hynes)
9:00 PM - Y8.1
Stable Metallic and Bimetallic Catalysts Embedded in Porous Oxide Supports.
Anumol Ashok 1 , Viswanath Balakrishnan 1 , Ravishankar Narayanan 1
1 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractNoble metal and bimetallic nanoparticles are vital for catalyzing various industrially important reactions. The size, shape and composition of the material play important roles in the catalytic activity. One of the common problems associated with nanoparticles catalysts is the deterioration that takes place due to coarsening/sintering of the particles. The thermal stability of noble metal nanoparticle catalysts can be improved by using stable reducible or non-reducible oxides such as ceria, silica and titania as matrices for catalyst dispersion. We demonstrate a new method to prepare a variety of oxide supports with controlled porosity and crystallinity by controlled aggregation of nanoparticles and subsequent thermal treatments. The mechanism of evolution of the porous structure will be presented. A novel method based on heterogeneous nucleation of a precursor phase has been developed to disperse ultrafine metallic and bimetallic catalysts based on Pt/Au on such supports. The catalytic action for methanol oxidation and water-gas shift reactions and the structure/stability of these supported catalysts will be presented using a combination of advanced spectroscopy and electron microscopy including in-situ techniques
9:00 PM - Y8.10
Selective Methanation of CO Catalyzed by Ru-Modified Mesoporous Ni-Al Oxides.
Aihua Chen 1 , Toshiro Miyao 1 , Kazutoshi Higashiyama 1 , Hisao Yamashita 1 , Masahiro Watanabe 1
1 Fuel Cell Nanomaterials Center, University of Yamanashi, Kofu, Yamanashi Japan
Show AbstractSelective methanation of CO has been proposed as one of the promising methods to remove CO levels to lower than 10 ppm in hydrogen-rich gases, in order to meet the requirement of the working environment of the polymer electrolyte membrane fuel cell (PEMFC). However, until now, it still remains a challenge to make use of this method due to severe requirements for selectivity and activity.Mesoporous materials, ever since the first report of MCM-41 in 1992, have been extensively explored for practical applications in the catalysis area. Their characteristics of high surface area have been applied to provide higher dispersions of active sites for loaded metal particles than those of conventional materials. In this work, mesoporous Ni-Al oxide composites, synthesized by a one-pot method,1 denoted as MA-xNi, where x is the molar ratio of Ni/(Ni+Al), have been modified by 1 wt% Ru, to be employed as a catalyst for selective CO methanation.According to the XRD results, the original amorphous MA-xNi converted to NiAl2O4 and γ-Al2O3 when reduced by H2 at 400°C in the presence of Ru. Simultaneously, part of the NiO was reduced to form highly dispersed Ni nanoparticles several nanometer in size, which was also confirmed by STEM. These characteristics give the catalyst high activity and selectivity for the selective CO methanation, which was studied systematically through kinetic measurements with a fixed-bed quartz tubular reactor at atmospheric pressure with a feed gas of 1 vol% CO, 20 vol% CO2, H2 balance in the dry base, and a space velocity of 2400 h-1. The ratio of steam to CO was adjusted to 15. In the case of 1 wt% Ru/MA-33Ni, CO outlet levels lower than 10 ppm had been achieved when the reaction temperature ranged from 190 ~270°C with negligible CO2 conversion when the reaction temperature was below 245 °C ( since the generated CH4 concentration is lower than 2%), indicating the high activity and selectivity of this catalyst. Furthermore, the influence of Ni concentration on the activity and selectivity was studied in detail. Reference1. Morris, S. M.; Fulvio P. F.; Jaroniec. M. J. Am. Chem. Soc. 2008, 130, 15210-15216.Contact author:
[email protected] 9:00 PM - Y8.11
Selective Catalytic Reduction of CO2on Pt/TiO2 Photocatalyst.
Qin-Hui Zhang 1 , Wen-Dong Han 1 , Yi-Juan Hong 1 , Jian-Guo Yu 1
1 , State Key Lab of Chemical Reaction Engineering, College of Chemical Engineering, East China University of Science and Technology, Shanghai China
Show AbstractThe CO2 conversion to chemically valuable species is important in developing alternative fuels and various raw materials for different industries. It also aids in preventing the continuous rise in global temperature due to the green house effect of CO2. In this paper a brief overview of the CO2 chemical reduction is presented. Further, a gas-solid heterogeneous system for solar-chemical energy conversion of CO2-SCR (Selective Catalytic Reduction) with H2O on various nanostructure photocatalysts is discussed, in which, the H2O serves as hydrogen resource (or reducing agent) and CO2 as carbon resource (or oxidant), UV/Visible light provides the reaction energy and the prorous semiconductor provides the active centers for such a photocatalysis process to ultilize the solar energy through chemical conversion or storage process. Last, various crystal phase (rutile or anatase) and size (2-20 nm) of low dementional nano-TiO2 (particle, ribbon or tube) and Pt supported/composite photocatalysts are synthesized via the sol-gel and high temperature hydrothermal methods. The catalysts are characterized with powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), photoluminescence and the photocatalytic reduction of CO2 with H2O to produce chemically valuable compound such as CH4 or CH3OH are among the most desirable and challenging goals.
9:00 PM - Y8.13
The Nanophysics of TiO2/Au Model Catalyst as a Key to Understanding the High Efficiency of Real Au/TiO2 Catalyst and Technological Consequences.
Tamerlan Magkoev 1 , Dmitrij Panteleev 1 , David Remar 1 , Anatolij Turiev 1 , Natalija Tsidaeva 1 , Georgij Vladimirov 2 , Katsuyuki Fukutani 3
1 , University of North Ossetia, Vladikavkaz Russian Federation, 2 , University of Saint Petersburg, Saint Petersburg Russian Federation, 3 , University of Tokyo, Tokyo Japan
Show AbstractAbout a decade ago it was found that catalytic activity for a range of oxidation reactions, (most notably carbon monoxide oxidation) of a mixture of Au ultrasmall particles with titanium oxide powder considerably exceeds that exhibited by Au or titania on their own. For understanding of the origin of such an enhanced activity of Au/TiO2 an extensive research of the corresponding well-defined model catalyst has been carried out. In spite of this the explanation of high catalytic activity of titania/Au is still controversial. On one hand it is considered that it is due to the unique electronic and/or structural properties of oxide supported nanometer-scale Au particles, on the other – to the effect of the Au/titania perimeter interface. To overcome this controversy it would be informative to study the catalytic behavior of the system which emphasizes one of the two above-mentioned parameters, either an Au ultra-small cluster or titania/Au perimeter interface effect. The real catalyst is hardly suitable for thus purpose, however the model system might be a good candidate. In relation to this the aim of the present study is to investigate the CO + O2 interaction on the surface of the system obtained by the controlled growth of titanium oxide submonolayer to multilayer thin film islands on the surface of atomically clean Au(111) by a set of surface sensitive techniques: scanning tunneling microscopy, Auger electron and X-ray photoelectron spectroscopy, low energy ion scattering, Fourier-transform infrared spectroscopy.It was found that CO molecules which do not adsorb on both titanium oxide and Au(111) surface separately held at a temperature of 200 K, can easily be adsorbed on the formed titania/Au(111) system at the same temperature. Adsorption place of such species is the oxide/metal perimeter interface. Subsequent inlet of molecular oxygen into the vacuum chamber results in quite efficient carbon monoxide surface concentration decay due to carbon dioxide formation and its subsequent desorption. Efficiency of this process increases with the decrease of carbon monoxide initial concentration thus pointing at the importance of the free surface sites at the oxide/metal interface for the reaction. For the technological perspective the results obtained offer the following steps to gain the performance of the Au/TiO2 catalysts: 1) to produce smaller gold particles to increase the Au/TiO2 perimeter interface length; 2) to supply the reaction CO+O2 mixture to the catalyst at lower pressure to enhance the oxidation rate.The work was supported by Russian Agency for Education (contract # 2.1.1/3938) and RFBR-JSPS (grant # 09-02-92109-YaF_a).
9:00 PM - Y8.14
Water-soluble Poly(4-styrenesulfonic acid-co-maleic acid)-stabilized Nickel(0) and Cobalt(0) Nanoclusters as Highly Active Catalysts in Hydrogen Generation from the Hydrolysis of Ammonia-Borane.
Onder Metin 1 , Saim Ozkar 1
1 Chemistry, Middle East Technical University, Ankara Turkey
Show AbstractWater soluble poly(4-styrenesulfonic acid-co-maleic acid), PSSA-co-MA, stabilized nickel(0) and cobalt(0) nanoclusters were for the first time prepared from the reduction of nickel(II) chloride and cobalt(II) chloride, respectively, by a minimum amount of sodium borohydride shortly before their usage as catalyst for hydrogen generation from the hydrolysis of ammonia-borane in same medium at room temperature. PSSA-co-MA stabilized nickel(0) and cobalt(0) nanoclusters having average particle size of 2.1 ± 0.6 and 5.2 ± 1.6 nm, respectively, were isolated from the reaction solution and characterized by TEM and UV-Visible electronic absorption spectroscopy. PSSA-co-MA stabilized nickel(0) and cobalt(0) nanoclusters are highly active catalysts for hydrogen generation from the hydrolysis of ammonia-borane at low temperature. PSSA-co-MA stabilized nickel(0) and cobalt(0) nanoclusters provide 22450 and 17650 turnovers, respectively, in the hydrogen generation from the hydrolysis of ammonia-borane at 25 °C before deactivation. Catalytic hydrolysis of ammonia-borane is first order with respect to the catalyst concentration, but zero order with respect to the substrate concentration in the case of both nickel(0) and cobalt(0) nanoclusters. Activation energies for the hydrolysis of ammonia-borane in the presence of PSSA-co-MA stabilized nickel(0) or cobalt(0) nanoclusters (32 ± 2 kJ.mol-1 and 34 ± 2 kJ/mol, respectively) are smaller than most of the values reported for the same reaction in the presence of other catalyst systems.
9:00 PM - Y8.15
The Pt Size in Pt/Ba/Al2O3 NOx Storage-reduction Catalysts made by Flame Spay Pyrolysis (FSP).
Robert Buechel 1 2 , Alfons Baiker 2 , Sotiris E. Pratsinis 1
1 D-MAVT, ETH Zurich, Zurich Switzerland, 2 D-CHAB, ETH Zurich, Zurich Switzerland
Show AbstractNOx storage-reduction (NSR) is successfully applied for exhaust gas treatment of lean fuel engines. Under fuel lean conditions, exhaust NOx is oxidized over a noble metal (Pt) and then trapped on an alkali- or alkaline earth metal (Ba) in the form of metal-nitrates. During the subsequent short fuel rich period the NOx originating from decomposition of the metal-nitrates is reduced on the metal component to nitrogen and the cycle restarts. [1]The noble metal (Pt) was found to play an important role in NSR systems [2] in order to oxidize NO under fuel lean conditions and to and reduce NOx species to N2 under fuel rich condition. To use Pt in the most efficient way, the available Pt is finely dispersed over the support, increasing the NO oxidation reaction. But higher Pt dispersions, and therefore smaller Pt clusters, do not always lead to the highest NSR conversion rates, as the catalytic activity of Pt is also a function of the coordination and geometry of the Pt and smaller Pt clusters tend to form PtOx.With a flame spray pyrolysis (FSP) setup catalyst powders with surface areas form 80 to 220 m2/g were produced with Pt dispersion of 5 to 15%. With higher SSA the Pt dispersion decreased, what is unexpected but was confirmed by counting Pt clusters on high resolution STEM pictures. The Pt was preferentially located on Ba and for small BaCO3 particles a bimodal size distribution of the Pt was seen, whereas for bigger BaCO3 particles the size distribution of the Pt clusters was becoming narrower. The measured NSR activity changes with particle size and can be correlated with the resistance of Pt to be oxidation under fuel lean conditions.References[1]W.S. Epling, L.E. Campbell, A. Yezerets, N.W. Currier, J.E. Parks, Cat. Rev. - Sci. Eng. 46 (2004) 163-245.[2]M.O. Symalla, A. Drochner, H. Vogel, R. Büchel, S.E. Pratsinis, A. Baiker, Appl. Catal., B 89 (2009) 41-48.
9:00 PM - Y8.16
Preferential Oxidation of CO Under Hydrogen-rich Condition Over Au-Ag Alloy Catalysts.
Luo Yichia 1 , Shih Wencheng 1 , Yen Chunwan 1 , Mou Chungyuan 1 2
1 Chemistry, National Taiwan University , Taipei Taiwan, 2 , National Taiwan University Center for Condensed Matter Sciences, Taipei Taiwan
Show AbstractAluminosilicate of thin film SBA-15(TF) was used as an acidic support, which was incorporated with gold and silver nanoparticles inside the mesoporous channel. These catalysts have been investigated with nitrogen adsorption, TEM, XRD, ICP-MS, UV-Vis spectroscopy, and EXAFS (X-ray absorption fine structure spectroscopy) and the corresponding reaction activity and selectivity for preferential oxidation of CO under hydrogen rich atmosphere have been measured. The Au-Ag nanocatalyst imparts superior activity for CO oxidation at low temperature. Supported Au-Ag nanoparticles have been shown to exhibit an alloying structure by EXAFS fitting. The BET surface areas of the catalysts were between 400 and 520 m2/g with the pore sizes about 5 nm and total metal loading amounts around 5 wt%. The Au-Ag alloy SBA-15(TF) supported catalysts experimentally showed near 100% CO conversion at 80°C and about 70% of selectivity at 40-80°C.
9:00 PM - Y8.17
Preparation of Platinum Nanoparticles Using Linear Polyethyleneimine as a Stabilizer by Liquid-phase Reduction Method.
Takanori Imai 1 , Takashi Kajiwara 1 , Yoshimoto Abe 2 , Keishi Nishio 3 , Ryuji Tamura 3 , Hirobumi Shibata 3 , Tohru Kineri 4 , Takahiro Gunji 1
1 Department of Pure and Applied Chemistry, Tokyo University of Science, Noda, Chiba, Japan, 2 , Tokyo Seiei College, Nishi-Koiwa, Katsushika, Tokyo, Japan, 3 Deparmtent of Materials Science and Technology, Tokyo University of Science, Noda, Chiba, Japan, 4 Department of Applied Chemistry, Tokyo University of Science, Yamaguchi, SanyoOnoda, Yamaguchi, Japan
Show Abstract The preparation of platinum nanoparticles using linear polyethyleneimine and their properties will be presented. Metal nano particles are expected to be applied as a sensor, a nano device, an electrode, and a coloring-matter material because these nano particles show the special properties depending on size. Moreover, the application as a catalyst is also expected by taking advantage of the specific surface area of the nano particles. Platinum nano particles are prepared by the liquid-phase-reduction method which platinum complex is reduced in the solution of protective agents. Micelles and organic polymers are commonly used as protective agents which have low adsorption ability to coagulate the platinum nano particles at lower pH. In this paper, therefore, the preparation of platinum nano particles, which are stably dispersed at low pH, will be reported by using linear polyethyleneimine (LPEI) as a protective agent. LPEI (Mw 2150 or 25000) was dissolved in water or ethanol and dihydrogen hexachloroplatinate(IV) hexahydrate was added with stirring. Sodium borohydride aq. was added followed by heating for several hours. After concentration under reduced pressure, platinum nano particles were obtained by reprecipitation or filtration. Platinum nano particles were successfully prepared as black powder by the reduction using sodium borohydride. Platinum nano particles were dispersed in water and ethanol. A stable dispersion was obtained by changing the pH in the range of 1 to 6. The diameter of platinum nano particles was evaluated by transmission electron micrography to be 3.26 nm (Mw 25000) and 1.76 nm (Mw 2150). Platinum nano particles were also prepared by using a mixture of LPEI and branched polyethyleneimine in the same procedure. These nano particles were isolated as brown ore black highly viscous liquid. These nano particles were dispersed in water when the pH was changed from 0 to 10.
9:00 PM - Y8.18
Catalytic Activities of Sonochemically Synthesized Au-Pd Core-shell Nanoparticles.
Noboru Taguchi 1 , Shingo Tanaka 2 , Tomoki Akita 2 , Masaya Matsuoka 1 , Masanori Kohyama 2 , Akihiro Iwase 1 , Fuminobu Hori 1
1 Department of Materials Science, Osaka Prefecture University, Sakai, Osaka Japan, 2 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka Japan
Show AbstractAu-Pd binary nanoparticles were synthesized by sonochemical reduction method, and their structure was studied by HRTEM and STEM observation. We also measured catalytic activity for hydrogenation of these Au-Pd nanoparticles using 4 pentenoic acid. The mean diameter of all nanoparticle were about 9 nm and their structure were core shell phase separated (Au-core and Pd-shell). The thickness of Pd shell can be controlled well by changing the content ratio of Au3+ and Pd2+ ions. The lattice space of surface Pd layer was expanded and had epitaxially grows on Au-core lattice. [1, 2] This lattice space of surface Pd layer decreases to that of pure Pd bulk with increasing the Pd shell thickness (up to about 2 nm). Au-Pd core shell nanoparticles showed higher catalytic activities for hydrogenation than Pd nanoparticle. Catalytic activety of these nanoparticles varies from their structure. However, the catatlitic activities dose not neccessary correspond to the particle lattice space linearly. Our preriminaly first principles calculation shows that local density of state at a few Pd layers stacked on Au with coherent interface is affected by Au substrate. It is supposed that lattice expansion, Pd-shell thickness and Au/Pd interface affect catalytic activities multiply. [1] H. Takatani, H. Kago, Y. Kobayashi, F. Hori, and R. Oshima,Trans. Mater. Res. Soc. Jpn. 28, 871 (2003). [2] T.Akita, T.Hiroki, S.Tanaka, T.Kojima, M.Kohyama, A.Iwase and F.Hori Catalysis Today 131 pp.90-97 (2008)
9:00 PM - Y8.19
Mechanism of Environment-dependent Structural Changes of Au Nanoparticles on CeO2 by First-Principles Approach.
Shingo Tanaka 1 , Tomoki Akita 1 , Masanori Kohyama 1 , Seiji Takeda 2
1 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka Japan, 2 Graduate School of Science, Osaka University, Toyonaka, Osaka Japan
Show AbstractAu nanoparticles supported on metal oxide substrates exhibit remarkable catalytic activity such as low-temperature CO oxidation [1] and Au/CeO2 systems show remarkable catalytic activity for water gas-shift (WGS) reaction at low temperature and CO oxidation [2-4]. Recent analytical transmission electron microscope (TEM) observations for Au/CeO2 revealed novel dynamic structural changes of Au nanoparticles deposited on CeO2 surfaces [5-8]. The Au particles rapidly shrunk layer by layer to Au monolayer during the observations and the particles recovered after the observations were stopped. In order to clarify the mechanism of novel structural changes, we have performed the first-principles calculations of Au/CeO2(111) systems using the projector augmented-wave (PAW) program code [9-12]. The calculated Au-Ce interlayer distance of non-stoichiometric Ce-terminated interface (0.277 nm) is close to that obtained from a high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observation (0.27 nm) [8]. The analyses of free energies as a function of chemical potential of oxygen revealed that under the condition of TEM observation, with electron beam irradiation and a strong reducible condition, the Ce-terminated interface is rather stable and Au atoms diffused from Au particles are trapped by the surface oxygen vacancies, while the O-terminated interface is stable when the TEM observation is stopped. The environment-dependent structural change can be explained by cyclic process that surface diffusion and trapping the oxygen vacancies of Au atoms. In this process, it is important factor that the Au monolayer region on CeO2 survives through the TEM observations [5-8]. The present novel structure changes are related to the catalytic activity of Au/CeO2 system. This work was supported by Grant-in-Aid for Specially Promoted Research (19001005), the Japan Society for the Promotion of Science Research (JSPS). [1] M. Haruta, Catal. Today 36, 153 (1997). [2] Q. Fu et al., Catal. Lett. 77, 87 (2001). [3] R. Burch, Phys. Chem. Chem. Phys. 8, 5483 (2006). [4] Sakurai et al., Appl. Catal. A Gen. 291, 179 (2005). [5] T. Akita et al., J. Mater. Sci. 40, 3101 (2005) [6] T. Akita et al., Catal. Today 117, 62 (2006). [7] T. Akita et al., Catal. Today 122, 233 (2007) [8] T. Akita et al., J. Mater. Sci. 43, 3917 (2008). [9] S. Ishibashi et al., J. Phys. Soc. Jpn. 75, 015005 (2006). [10] S. Tanaka et al., Mater. Trans. 47, 2690 (2006). [11] S. Ishibashi et al., J. Phys. Soc. Jpn. 77, 053709 (2008). [12] T. Tamura et al., Phys. Rev. B 77, 085207 (2008).
9:00 PM - Y8.2
Atomic and Molecular Adsorption on Pure and Metal-decorated, Mesoporous Carbon Substrates.
Andrea Freitag 1 , Hangning Chen 1 3 , Nathaniel Bass 1 , Andrew Lupini 2 , J. Larese 1 2
1 Chemistry, University of Tennessee Knoxville, Knoxville, Tennessee, United States, 3 , Lanzhou University, Lanzhou China, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractMesoporous carbon materials have been intensively studied for their potential as catalysts, fuel cell electrodes, gas storage and separation materials. Details of surface morphology, structure and chemistry could have significant effect on interaction with atomic and molecular adsorbates such as H2 and methane and thus on their usefulness in energy related applications. A systematic investigation of the adsorption properties of small molecules will provide a basic understanding of the substrate requirements needed to realize the desired functionality. Adsorption on pure and Pd decorated mesoporous amorphous carbon membranes with various pore diameters derived from silica templates has been studied using high resolution adsorption isotherms in the temperature range between 10 and 20K. Thermodynamic quantities deduced from the isotherm measurements are compared to those obtained on the equivalent substrates without the metal nanoparticles present. This work was supported by U.S. DOE Basic Energy Science, with contract no. DE-AC05-00OR22725 with ORNL.
9:00 PM - Y8.20
Characterization of Platinum-based Bimetallic and Trimetallic Alloy Nanoparticle Catalysts for Fuel Cell Applications.
Rameshwori Loukrakpam 1 , Bridgid Wanjala 1 , Bin Fang 1 , Peter Njoki 1 , Jin Luo 1 , Chuan-Jian Zhong 1
1 Department of Chemistry , State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractFuel cell technology is an increasingly-important field of research today in both academic and industrial settings because of energy and environmental concerns. Fuel cells have the advantage of high efficiency and being environmentally clean. One major challenge for the commercialization of fuel cells has been the high cost of catalysts. Platinum is the best known catalyst for fuel cell but has major drawbacks like high cost, low activity, and poor stability. Reduction of amount of platinum while increasing activity and stability is desired in the development of advanced catalysts. This presentation reports results of the characterization of some platinum-based bimetallic and trimetallic nanoparticles (e.g. PtCr, PtNi, PtNiW, PtNiZr etc). The nanoparticles synthesized in this work have controllable sizes ranging from 1 to 10 nm and are characterized using different techniques including TEM, DCP-AES, HRTEM, XRD, EDS, XPS, etc. The results show that composition and other structural characteristics of the nanoparticles can be controlled. Results from electrochemical and fuel cell testing of selected catalysts in oxygen reduction reaction will also be discussed, along with insights from a combinatorial study of the optimized composition for the design of fuel cell catalysts
9:00 PM - Y8.21
Alloy and Core-Shell Morphologies of Gold-Platinum Nanoparticle Catalysts For Fuel Cell Reactions.
Bridgid Wanjala 1 , Derrick Mott 1 , Rameshwori Loukrakpam 1 , Peter Njoki 1 , Jin Luo 1 , Chuan-Jian Zhong 1
1 Department of Chemistry , State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractThe ability to prepare metal nanoparticles with controlled alloy or core shell morphologies is important for the development of electrocatalysts for fuel cell reactions. This presentation reports recent results of an investigation of the alloy and core-shell morphologies of gold-platinum nanoparticles as catalysts for fuel cell reactions. The AuPt nanoparticle catalysts were prepared by a modified two-phase synthesis protocol employing organic monolayer encapsulation on the bimetallic cores. The size- and conposition-controlled nanoparticles were assembled on carbon support materials with controllable dispersion and metal loading, and were thermally activated under controlled temperature and atmosphere. Characterizations of the structures and morphologies were carried out using an array of techniques such as direct current plasma - atomic emission spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and higher resolution transmission electron microscopy. The characterization of the electrocatalytic properties is carried out by cyclic voltammetry and rotating disc electrode techniques. The phase properties are shown to depend on a number of factors such as size, composition, support, and calcinations temperature. This paper focuses on recent results of the study of the effect of thermal treatment temperature on alloying or phase-segregation properties of the bimetallic nanoparticles and on the electrocatalytic activity for oxygen reduction reactions. The understanding of how the catalyst calcination temperature influences the activity and phase properties of the bifunctional bimetallic nanoparticle catalysts has important implications to the design of highly-active and stable catalysts for fuel cells.
9:00 PM - Y8.22
Evaluation of Nanostructured Multimetallic Catalysts in Proton Exchange Membrane Fuel Cells and Direct Methanol Fuel Cells.
Bin Fang 1 , Jin Luo 1 , Peter Njoki 1 , Rameshwori Loukrakpam 1 , Bridgid Wanjala 1 , Jun Yin 1 , Chuan-Jian Zhong 1
1 Department of Chemistry , State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractPolymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are becoming increasingly attractive power sources for a wide range of applications because of their high energy conversion efficiencies and low pollution. A major challenge to the commercialization of PEMFCs and DMFCs is the poor performance of existing catalysts. The ability to engineer multimetallic nanoparticles in terms of size and composition represents an important approach to the development of active, robust and low-cost fuel cell catalysts. Built upon our ability to synthesize and process nanostructured multimetallic (e.g., PtVFe, PtNiFe, etc.) nanoparticles for oxygen reduction reaction and methanol oxidation reaction, this presentation reports our recent findings in the evaluation of the nanostructured materials as cathode catalysts in PEMFCs and anode catalysts in DMFCs. The results for some of the promising catalysts in achieving the targeted performances in PEMFCs and DMFCs will be discussed.
9:00 PM - Y8.23
Photocatalysis by TiO2 Incorporated with Gold Nanoparticles.
Byoung Koun Min 1 , Na Kyoung Youn 1 , Oh Shim Joo 1 , Hyunjoo Lee 1
1 , Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractIncorporation of noble metal nanoparticles has been expected to assist an efficient charge separation of photogenerated charge carriers leading to promoting the photocatalytic activity of TiO2. Gold nanoparticle is particularly of interest because of its typical optical property, surface plasmon resonance, which has been considered to a key factor of an increase of photocatalytic activity of TiO2 in several aspects. Herein, in order to elucidate more fundamental basis of Au/TiO2 as a photocatalyst we performed photocatalytic decomposition of 1,4-dioxane in water using various Au/TiO2 powders whose size and/or morphology were varied by leaching method. Particularly, we focused on the relationship between the intensity of surface plasmon absorption and photocatalytic activity. Our results show that typical Au state on TiO2 reveals two times higher activity compared to the commercial TiO2 photocatalyst (P25). More importantly, we found that the behavior of photocatalytic activity is strongly correlated with that of surface plasmon absorption of gold nano-particles. In addition, we extended the study of the photocatalytic activity of TiO2 modified with gold nanoparticles to the kinetics of 1,4-dioxane photodegradation as a case study. The relationship between the kinetics and the concentration of dissolved oxygen was also discussed in the presentation.
9:00 PM - Y8.24
Preparation of Pt Nanoparticles Dispersed in Mesoporous Silica.
Yukitoshi Chiba 1 , Hirobumi Shibata 1 , Daichi Nagata 1 , Takahiro Gunji 2 , Ryuji Tamura 1 , Tohru Kineri 3 , Keishi Nishio 1
1 Deparmtent of Materials Science and Technology, Tokyo University of Science, Noda-shi, Chiba, Japan, 2 Department of Pure and Applied Chemistry, Tokyo University of Science, Noda-shi, Chiba, Japan, 3 Deparmtent of Applied Chemistry, Tokyo University of Science, Yamaguchi, Sanyoonoda-shi, Yamaguchi, Japan
Show Abstract Mesoporous materials synthesized using molecular self-assemblies of surfactants as templates have highly ordered pore structures and a large surface area, which makes them promising candidates as the matrix of novel nanoparticle catalysts. In particular, mesoporous silica is a very stable material at high temperatures in air, and Pt is a very useful material for catalysts. In this work, Pt nanoparticles were dispersed in mesopores of mesopous silica by using a sol-gel process with a composite template consisting of an amphilic triblock copolymer (Pluronic P123 or F127) and a Pt-organic complex, which was prepared with K2Pt(II)Cl4 as a Pt source and 1,10-phenanthroline as a chelating agent. The obtained Pt-1,10-phenanthroline complex did not dissolve in several solvents, e.g., hexane, benzene, toluene, THF, H2O, CH3OH, and C2H5OH. However, when the Pt-1, 10-phenanthroline complex was reacted with ethylenediamine it dissolved in many solvents. Platinum nanoparticles dispersed in mesoporous silica were obtained using a sol-gel process with a complex template consisting of Pt-1, 10-phenanthroline-ethylenediamine, and an amphilic triblock copolymer (Pluronic P123 or F127). A sample dried at 353 K was bright yellow. When it was subsequently heat-treated at 823 K, it turned light gray. This change indicates that Pt nanoparticles can be obtained by heat-treatment at a high temperature because, to generate Pt nanoparticles, the organics chelated to Pt ions must be removed. Measurements from small-angle x-ray scattering show that mesoporous silica obtained by using a complex template has a much more highly ordered pore structure than that obtained by using only an amphilic triblock copolymer. It has both large pores (above 8 nm) and a large surface area (about 290 m2/g). Furthermore, results of a TEM investigation showed that Pt nanoparticles were generated only in mesopores of mesoporous silica.
9:00 PM - Y8.25
Hydrogen Production by Ethanol Steam Reforming over Supported Cu-Ni Bimetallic Nanoparticles.
Li-Chung Chen 1 , Shawn D. Lin 1
1 Chemical Engineering, National Taiwan University of Science and Technology, Taipei Taiwan
Show AbstractBimetallic CuNi/SiO2 catalysts of different Cu/Ni ratios were prepared by either an incipient wetness impregnation (IM) method or a MeOH-PVP nanoparticles loading (NL) method. Both methods resulted in catalysts with well-dispersed nanocrystals of 1 - 3 nm size. Calcination in Air or in N2 at 673K was used to remove PVP from the CuNi/SiO2 (NL) catalysts. XRD results was indicate that IM and NL catalysts are different and the latter seem less susceptible to changes by calcination.EXAFS analysis indicate that 573K- reduced catalysts still contained oxygen in the bonding neighbors to both Cu and Ni at a different extent of th two catalysts. Both catalysts catalyze ethanol steam reforming to nearly 100% conversion at 573K, WHSV=5h-1 ,and H2O/EtOH=5. However, the product selectivitys are different for two catalysts. The NL catalyst produced mainly acetone while the IM catalyst produced mainly acetaldehyde at 573K. At temperature higher than 623K, both catalysts results in similar product distribution. The relation between catalyst morphology and ethanol steam reforming product selectivity will be discussed.
9:00 PM - Y8.26
Ion Beam Modification of Pt Electrocatalyst Nanoparticles for Polymer Electrolyte Membrane Fuel Cells.
Tetsuya Yamaki 1 , Shunya Yamamoto 1 , Teruyuki Hakoda 1 , Hiroshi Koshikawa 1
1 Quantum Beam Science Directorate, Japan Atomic Energy Agency, Takasaki, Gunma, Japan
Show AbstractPolymer electrolyte membrane fuel cells (PEMFCs) have been receiving attention because of their highly attractive properties as a power source for portable, stationary, and automobile applications. While one of the major obstacles that should be overcome for the commercialization of PEMFCs is to find more efficient catalysts, nanoparticles of Pt and Pt-group metals are still the main catalyst widely employed in PEMFCs. This study concerns our attempt to improve catalytic properties of these materials by modification with ion beams. High-energy ion beams have been used extensively for surface treatment of bulk materials as well as elemental or structural analysis, because they can focus huge energy on the target materials in a concentrated form compared with the other ionizing beams. We expected that such a completely high electronic excitation could achieve new atomic arrangement and electronic states at the nanoparticle surface. Pt nanoparticles were prepared on a glassy carbon plate by a sputtering method and then irradiated with proton beams at energies of 0.38 and 10 MeV at room temperature. Cyclic voltammetry in a 0.5 M H2SO4 aqueous solution suggested that the lower-energy beam irradiation enhanced the active surface area of the Pt nanoparticles, calculated from the coulombic charge for hydrogen adsorption. Thus, the nanoparticles will be modified by the proton-beam excitation so that they have higher surface reactivity. The mechanism determining this irradiation effect seems to be rather complicated and is still unclear at present, but we may discuss it in relation to a change in the interfacial crystal structure induced by the irradiation. One of the authors (T.Y.) acknowledges the financial support from a Grant-in-Aid for Scientific Research (KAKENHI) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
9:00 PM - Y8.28
Reduction Rate of Pd Nanoparticles Synthesis Process in Solution Plasma.
Junko Hieda 1 , Nagahiro Saito 2 3 , Osamu Takai 1 3
1 , Graduate School of Engineering, Nagoya University, Nagoya Japan, 2 , EcoTopia Science Research Institute, Nagoya University, Nagoya Japan, 3 , CREST/JST, Nagoya Japan
Show AbstractPlasma in the liquid phase (“solution plasma”) has attracted great attention because of its applicability to industrial materials processing. In particular, glow discharge in the liquid phase is a useful tool for the synthesis of metal nanoparticles. This method provides extremely rapid reactions using activated chemical species and radicals generated from plasma phase. Many methods for the synthesis of metal nanoparticles (e.g. mechanical synthesis, chemical or physical synthesis in the gas phase, and chemical reduction in the liquid phase) have been reported. Using the chemical reduction method, metal nanoparticles with excellent monodispersity of the particle size are obtained. However, this method requires a reducing agent to fabricate metal nanoparticles from a solution containing metal ions. The use of a solution plasma would allow the rapid fabrication of the metal nanoparticles without adding any reducing agents, because plasma in the liquid phase provides highly excited energy states of atoms, molecules and radicals formed from the solution molecules. In order to control the synthesis, the elucidation of the reaction mechanism between active species and metal ion is required.In this study, we demonstrated the synthesis of the palladium nanoparticles using solution plasma process. Furthermore, the reaction between the palladium ion and the active species from solution plasma was investigated.The palladium nanoparticles were synthesized through the reduction of the metal ion with a discharge in an aqueous solution containing tetrachloropalladate (II) as a metal source. Dodesyl sodium sulfate (SDS) and polyvinylpyrrolidone (PVP) were used as surfactants. One of these surfactants was dissolved into deionized distilled water and subsequently tetrachloropalladate (II) solution was added to the solution. The concentration of [PdCl4]2- ion was 0.3 mM. The solution pH was adjusted by adding hydrochloric acid.The discharge was generated by using a bipolar pulsed power supply. The applied voltage was about 2400 V. The pulse frequency and the pulse width were 15 kHz and 2 μs, respectively. The crystal structure of the obtained nanoparticles was identified by X-ray diffraction (XRD) method. The size and the morphology of the nanoparticles were observed by transmission electron microscopy (TEM). The relation between the reduction rate of the [PdCl4]2- ion and the relative amount of the active species present in the plasma (e.g. H, O and OH radicals) estimated from the emission spectra at various solution pH values will be discussed.
9:00 PM - Y8.29
Synthesis and Characterization Of Freeze-dried Ag/TiO2 Nanocomposites.
Marcelo Viana 1 , Aurellis Nascimento 1 , Nelcy Mohallem 1
1 , Federal University of Minas Gerais, Belo Horizonte Brazil
Show AbstractAg/TiO2 nanocomposites have gained attention for its strong bactericide power and its photocatalytic property. In this work, Ag/TiO2 was prepared from a precursor solution of titanium isopropoxide (IV) and silver nitrate by coprecipitation. After precipitation at room temperature, this material was freeze-dried and calcined at various temperatures between 200 and 1200°C. The samples were characterized by X-ray diffraction, TGA-DTA analysis, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The density, specific surface area and porosity were determined by helium pycnometry and gas adsorption, respectively. The nanocomposites obtained showed texture, structure and morphology different according to calcination temperature.
9:00 PM - Y8.3
Bimetallic Nanoparticles of PtCu and PtNi; Synthesis and CO Oxidation Catalysis.
Takao Yamamoto 1 , Takashi Nakagawa 1 , Satoshi Seino 1 , Hiroaki Nitani 2
1 Department of Management of Industry and Technology, Osaka University, Suita, Osaka, Japan, 2 Institute of Materials Structure Science, KEK, Tsukuba, Ibaraki, Japan
Show AbstractBimetallic nanoparticles of PtCu and PtNi supported by iron oxide particles were synthesized by a new method employing a 4.8-MeV electron beam as a trigger for reduction of their aqueous ions, and their CO oxidation catalysis was evaluated to find activities enhanced by the alloying. Sample materials of PtCu (PtNi) bimetallic grains supported on γ-Fe2O3 particles were synthesized by irradiating with the electron beam a glass vial containing precursors in an aqueous solution. The vial contains aqueous ions of platinum and copper (nickel) and γ-Fe2O3 particles of average size of 30 nm. The irradiation induces water radiolysis generating reducing species, such as hydrated electrons, and metallic nanograins are formed and stabilized on the support material. The irradiation was finished in several seconds without using any organic solvent and any surfactant. The average grain sizes observed with a TEM were around 3 nm in diameter. XRD patterns of PtCu samples exhibited the FCC structure with peak shifts obeying the Vegard’s low at low Cu concentrations. X-ray absorption spectra measured at edges of the constituent elements indicated that Pt is in the metallic state and coordinates certainly with Cu or Ni. Catalytic activity of CO oxidation of the material was evaluated by measuring residual CO contents in air in contact with the sample material by using a gas-chromatograph. The activities of the PtCu and PtNi samples were higher than that of monolithic Pt on γ-Fe2O3. The correlation between the atomic structure in these nanograins and their activities was investigated, which indicated that the random alloy enhances the activity. These bimetallic nanoparticles are expected as catalysts for preferential oxidation of CO in hydrogen gas fed to fuel cells.
9:00 PM - Y8.30
Phase Behavior and Electrochemical Property of Platinum-Silver Bimetallic Nanostructures.
Zhenmeng Peng 1 , Hongjun You 1 , Hong Yang 1
1 Department of Chemical Engineering, University of Rochester, Rochester, New York, United States
Show AbstractWe present in this poster that platinum-silver mixed nanoalloys with composition in the entire composition range can be synthesized by a simultaneous co-reduction of their molecular precursors in a non-hydrolytic system, despite these two metals are largely immiscible as bulk materials.[1] Our results show that lattice parameter changes almost linearly with composition in these Pt-Ag nanomaterials and their correlations follow the Vegard’s law, a strong indication for the formation of metal alloys.[2] The contribution from surface energy, which can be negligible in bulks, is thought to attribute to this new phase behavior at the nanoscale. Usual structural behavior for platinum, such as transformation from face centered cubic (fcc) to another low symmetry crystalline phase, has been observed. Both experimental and density functional theory (DFT) studies show surface silver clusters play an important role in such structural change. These Pt-Ag nanostructures can be further treated and used as electrocatalysts in formic acid oxidation (FAOR). The optimized Pt-Ag catalyst exhibited a mass current density (Imass) of 2424 mA/mg-Pt at 0.6 V, close to 5 times of the value for a commercial Pt, which is 502 mA/mg-Pt. The relative increase of Imass is even more pronounced at lower potentials ranges, with over 13 at 0.2 V and 9 times at 0.4 V improvements over those for pure Pt. The large enhancement in its area-specific current density (Iarea) indicates an improved intrinsic activity. These results together with other unconventional Pt-M alloy electrocatalysts for proton exchange membrane fuel cells (PEMFCs) will be presented in this poster. References:(1)Peng, Z. M.; Yang, H. Designer platinum nanoparticles: Control of shape, composition in alloy, nanostructure and electrocatalytic property. Nano Today 2009, 4, 143-164.(2)Peng, Z. M.; Yang, H. Ag-Pt alloy nanoparticles with the compositions in the miscibility gap. J. Solid State Chem. 2008, 181, 1546-1551.
9:00 PM - Y8.31
TEM and HAADF-STEM Observation of Pt Particles Supported on Cerium Oxide.
Tomoki Akita 1 , Shingo Tanaka 1 , Koji Tanaka 1 , Masanori Kohyama 1 , Satoshi Shimada 2 , Masatake Haruta 2 , Seiji Takeda 3
1 , National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan, 2 , Tokyo Metropolitan University, Hachioji, Tokyo, Japan, 3 , Osaka University, Toyonaka, Osaka, Japan
Show AbstractPlatinum is typical precious metal used for catalysts, and it is widely utilized for various reactions such as purification of automobile exhaust gases, electrocatalyst of polymer electrolyte fuel cell etc.. The investigation of the interaction between metal particle and the support materials are important in order to control the particle size, inhibit the sintering and reduce the amount of precious metals. It is also expected that the synergy effect with the support materials directly improve catalytic properties. In this study, the structure of Pt particle supported on CeO2 is observed by transmission electron microscopy (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) in order to study the structure of the Pt-CeO2 interface in atomic scale. The Pt-CeO2 model structure was prepared by the vacuum deposition of Pt on poly-crystalline CeO2 substrate. The Pt-CeO2 interface structure is observed by profile-view HAADF-STEM with atomic scale by using JEOL JEM-3000F transmission electron microscope with accelerating voltage of 300kV. The orientation relationship of Pt(111)[-110]//CeO2(111)[-110] or Pt(111)[-110]//CeO2(111)[1-10] was often observed for the model structure. The distance between Pt atomic-layer and Ce atomic-layer was estimated as 0.26±0.01nm from the HAADF-STEM image. The estimation of three-dimensional shape of Pt particle was also examined by analyzing the intensity profiles of atomically resolved HAADF-STEM image. The truncated polyhedral shape surrounded by (111) and (100) surfaces which is expected from Wulff construction is derived and significant anisotropy was not found. The wide interface indicated the relatively strong interaction with CeO2 support, and adhesion energy of 1.7Jm-2 was obtained for the Pt-CeO2 interface. This work was supported by Grant-in-Aid for Specially Promoted Research (19001005), the Japan Society for the Promotion of Science
9:00 PM - Y8.32
Structural Properties of Bimetallic Clusters AumAgn (m+n=18) on the NOx (x=1,2,3) Adsorption Processes.
Bertha Molina 1 , Jorge Castro 1 2 , Jorge Soto 1 , Enrique Yepez 1 , Alipio Calles 1
1 Dep. Física, Facultad de Ciencias, UNAM., México D.F. Mexico, 2 Dep. Física, CINVESTAV del IPN, Mexico City, Del. Gustavo A.Madero, Mexico
Show AbstractIt has been shown that Au and Ag nanoparticles present catalytic properties of pollutant gases, product of the hydrocarbons combustion processes, whose efficiency is strongly dependant on their size, morphology and support material. The activity of Ag subnanometric particles supported on alumina in the NOx reduction mechanism, for the reaction HCSCR (Hidrocarbon Selective Catalytic Reduction), is a good example of these catalytic properties. It is also well established that both Au and Ag nanoparticles are oxygen poisoning resistant and that in certain reactions the bimetallic combination may be more efficient than their isolated parts. In this work we present a theoretical study of the NOx adsorption energies for different bimetallic clusters in the form AumAgn (m+n=18). It is also discussed the possible synergetic effect of different configurations, forming small Ag islands of one to five atoms, on the surface of the bimetallic cluster. The analysis is done using DFT in the ZORA approximation.
9:00 PM - Y8.33
Novel Synthesis and Atomic Level Characterization of PtSn/C Nanocatalysts for Direct Ethanol Fuel Cell Applications.
Jingyue (Jimmy) Liu 2 , Janet Braddock-Wilking 2 , Lawrence Allard 1
2 Center for Nanoscience and Dept. of Chemistry and Biochemistry, University of Missouri-St. Louis, St. Louis, Missouri, United States, 1 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe depleting amount of fossil fuels and the recent concerns about global warming have been the driving force for developing alternative and renewable energy sources such as biomass-derived liquid fuels. For applications in transportation or portable devices, direct ethanol fuel cell (DEFC) has recently attracted attention because of its non-toxicity, higher power density and renewability. The PtSn/C nanocatalyst is now considered as the most effective catalyst for the anode performance of DEFC [1]. The optimum Pt/Sn ratio and their degree of alloying, however, still remain controversial; furthermore, the catalyst preparation procedure can significantly affect the catalyst's nature and performance [2-3]. To better control the composition profile as well as the size distribution of PtSn nanoparticles, we recently focused on developing precisely defined molecular complexes as precursor materials. We expect that uniform dispersion of such molecular complexes onto catalyst supports, such as carbon black powders, and the subsequent controlled reduction processes may provide a novel route to fabricate PtSn nanoparticle catalysts with better alloying, desirable stoichiometry, a narrow particle size distribution and a better spatial distribution.The utilization of pre-formed and well-defined bimetallic/multimetallic clusters as catalyst precursors provides a novel route to develop desirable alloy nanoparticle catalysts and sub-Ångström resolution electron microscopy techniques provide deep insights into the surface atomic arrangement of metal and alloy nanoparticles as well as their structural dynamics. In-situ heating of the precursor materials inside an aberration-corrected (CEOS GmbH, Heidelberg, Ger) JEOL 2200FS microscope using a novel heating technology provided by Protochips Co. (Raleigh, NC) has given insights into the diffusion processes of molecules and atomic clusters and how the PtSn nanoparticles evolved. The heating technology [4] involves the use of unique MEMS-based heater chips that allow heating rates of 10**6 °C/sec, with extremely high specimen stability at the chosen temperature that permits image resolution in the deep sub-Å regime to be obtained within one minute after temperature changes. The latest results of the in-situ studies will be reported [5]. References1. Tsiakaras, P. J. Power Sources 171, 107 (2007).2. Zhou, W., Zhou, Z., Song, S., Li, W., Sun, G., Tsiakaras, P., and Xin,Q. Appl. Catal. B: Environ. 46, 273 (2003).3. Colmati, F., Antolini, and E. Gonzalez, E. Appl. Catal. B: Environ. 73, 106 (2007).4. Allard, L.F., Bigelow, W.C., Jose-Yacaman, M., Nackashi, D.P., Damiano, J. and Mick, S.E. J. Micros. Res. & Tech. 72:208–215 (2009)5. Research sponsored by Asst. Sec. for Energy Efficiency and Renewable Energy, Off. of Vehicle Technologies, at ORNL, managed by UT-Battelle LLC for the U.S. Department of Energy, under contract # DE-AC05-00OR22725; and by the University of Missouri.
9:00 PM - Y8.34
Synthesis of Pt-TM(transition metals) Catalysts and Their Hydrogenation Ability of Methyl Acrylate.
Miki Amari 1 , Keishi Nishio 1 , Hirobumi Shibata 1 , Tohru Kineri 2 , Takahiro Gunji 1 , Ryuji Tamura 1
1 , Tokyo University of Science, Noda, Chiba, Japan, 2 , Tokyo University of Science, Yamaguchi, Sanyo-Onoda, Yamaguchi, Japan
Show AbstractIn order to reduce the usage of Pt catalysts such as in automobile, one efficient way is to reduce the amount of Pt by alloying. In this work, we have prepared a number of Pt-TM(transition metals) alloys with various TM elements and evaluated their catalytic abilities by using the hydrogenation of methyl acrylate. For the sample preparation, Pt-TM mother alloys were prepared by arc-melting under Ar atmosphere and they were then crushed into powder of <20 μm. The characterization of the samples was performed by X-ray powder diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy (EDS). The surface area of the powders were evaluated by BET (Brunauer-Emmett-Teller) surface analysis and the catalytic ability was measured by hydrogenation of methyl acrylate in a reactor filled with hydrogen, sample powder (15 mg), methyl acrylate (1 ml) and C2H5OH (19 ml). During the reaction, the sample temperature was held constant by using a water bath. The catalytic ability was estimated by the reduction rate of hydrogen per unit surface area of the samples. The results show that high catalytic activities occur for the same crystalline structure, i.e., fcc structure, indicating that the crystal structure of a catalyst plays an important role in hydrogenation. In addition, for a certain TM element the catalytic activity was found to surpass that of Pt powder by a factor of two . Details of the results for a wide variety of TM elements will be discussed in the presentation.
9:00 PM - Y8.35
STEM Simulation of Pt3Co Nanoparticles for Hydrogen Fuel Cells.
Brian Patrick 1 , Paulo Ferreira 1
1 Materials Science and Engineering , The University of Texas at Austin, Austin, Texas, United States
Show AbstractHydrogen fuel cells, particularly proton exchange membrane (PEM) fuel cells, are a promising energy source for the future. PEM fuel cells have high currents, low startup times, and respond to load changes quickly. In order to produce energy, a platinum nanoparticle is currently used as a catalyst to dissociate the hydrogen molecule. Platinum is very expensive, therefore, Pt3Co nanoparticles are being investigated as a way to reduce the cost, as well as increase the overall effectiveness of the fuel cell. It is important to characterize the nanoparticles in order to find the shape and atomic distribution, which can give information to how the catalyst works. Pt3Co nanoparticles were imaged using angle annular dark field scanning transmission electron microscopy (HAADF/STEM). In order to characterize the shape and atomic distribution of the nanoparticles, computer simulations were employed. These images were analyzed using Digital micrograph and SimulaTEM to find the orientation of the particle as well as an initial shape. VESTA, a crystal builder was used to create the initial model of the particle, and then using xHREM, a high resolution transmission electron microscopy simulation software created the virtual HAADF/STEM micrographs. After simulation, the models were compared with the data, and, when necessary, simulated again. This process was repeated until the model was created an image consistent with the real image. The HAADF/STEM simulations were successful in identifying the Pt3Co particles orientation and shape as an imperfect truncated octahedron.
9:00 PM - Y8.36
Preparation and Characterization of Ni, Fe, and Co Nanocatalyst Supported onto Silica-Modified Alumina Aerogel for Chemical Looping Combustion.
Victor Abdelsayed 1 2 , Yuan Li 1 3 , Todd Gardner 1 , James Rall 4 , Mohindar Seehra 4 , R. Lloyd Carroll 1 2
1 , National Energy Technology Laboratory, Morgantown, West Virginia, United States, 2 Chemistry, West Virginia University, Morgantown, West Virginia, United States, 3 Chemical Engineering, West Virginia University, Morgantown, West Virginia, United States, 4 Physics, West Virginia University, Morgantown, West Virginia, United States
Show AbstractAerogels represent an excellent choice for catalytic supports, given their high porosity, high surface area, and wide thermal stability. These materials are especially well-suited for high-temperature transformational technologies such as Chemical Looping Combustion (CLC). In this work, we report the development of a simple method to incorporate different transition metals (M= Ni, Fe, and Co) as nanoparticles into silica-modified alumina aerogels. Surface area measurements reveal that the metal-loaded aerogels have a total surface area of 300-500 m2/g even after being calcinated in air at 800 oC for > 4 hours. The magnetic properties of these aerogel nanocomposites reveal that the iron-loaded samples are ferromagnetic while the corresponding cobalt-based ones are paramagnetic. XPS mapping shows that the metal oxide nanoparticles are evenly distributed inside the porous structures of the aerogels. TGA studies confirm that the metal oxide materials act as oxygen carriers in cyclic fuel-air reaction systems important in CLC. These results are confirmed by different other techniques (XRD, TEM, SEM, TGA, ICP-MS and XPS) that explore the structure, shape, and composition of the metallic nanoparticles inside the aerogels. Our method could be expanded to prepare multimetallic nanoalloy catalysts with novel properties that may lead to major technological breakthroughs in a variety of energy applications employing catalysts including fuel cells, water gas shift, Fischer-Tropsch, and biomass gasification.
9:00 PM - Y8.37
Highly Active Tantalum (V) Nitride Photocatalyst for Hydrogen Evolution under Visible Light.
Leny Yuliati 1 , Jae-Hun Yang 1 , Kazuhiko Maeda 1 , Tsuyoshi Takata 1 , Kazunari Domen 1
1 Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Tokyo Japan
Show AbstractThe need to obtain sustainable clean energy, such as hydrogen, has been increasing in the recent decades. One of the environmentally safe and benign methods would be photocatalytic water splitting. Since our aim is to utilize solar energy, there is no other way but to design a material that has a capability to perform a high activity under visible light. Some visible light driven photocatalysts have been discovered so far but only a few are able to absorb visible light up to 600 nm. One of them is Tantalum (V) Nitride (Ta3N5), which is known as a red pigment having an optical band gap of 2.1 eV. The activity of the Ta3N5 for photocatalytic hydrogen production from water splitting has been reported. However, unfortunately, the activity was still low even on Pt-deposited Ta3N5. In the present study, we succeeded in improving the activity of the Ta3N5 for hydrogen evolution by improving the surface area and reducing both the particle size and Ta(IV) defects. In the conventional method, the Ta3N5 was prepared by nitridation of Ta2O5 at 1123 K. In the present new method, we use mesoporous C3N4 having pore size of 7 nm as a template. TaCl5 was dissolved in EtOH as the precursor, which then was simply mixed with the mesoporous C3N4. The nitridation step was carried out at milder condition than that of the conventional method, i.e., 973 K. The newly prepared Ta3N5 showed a higher surface area (ca. 5 times) and has much lower particle size than the conventional one. Diffuse reflectance UV-visible spectra clearly showed the difference between these Ta3N5 materials. The conventional Ta3N5 showed a broad absorption above 600 nm, which would be due to the Ta(IV) defects, while the newly prepared Ta3N5 did not show such a tail absorption above the band edge absorption.The photocatalytic hydrogen evolution was carried out under visible light (λ > 400 nm) using methanol as a sacrificial agent. Pt as a cocatalyst was loaded on the Ta3N5 by photodeposition method. It was obtained that the newly prepared Ta3N5 showed much higher activity (ca. 9 times) than the conventional one. It is suggested that the enhanced activity would be due to the increase in the surface area and the decrease in the particle size and defects.
9:00 PM - Y8.38
Melon-SiO2 Nanocomposite – A novel Photocatalyst with Enhanced Activity Under the Visible Light.
Thiam Peng Ang 1 , Yen Mei Chan 1
1 , Institute of Chemical and Engineering Sciences, Singapore Singapore
Show AbstractA simple sol-gel method is used to prepare melon-SiO2 nanocomposite that has visible light absorption in UV-visible spectroscopy. It has been shown that the absorption of the nanocomposite is due to melon while, according to XPS and solid state NMR analysis, there is no intimate interaction between SiO2 and melon. The presence of melon in the nanocomposite is clearly indicated by FTIR, TGA, elemental analysis and TEM images. The nanocomposite has unexpectedly exhibited enhanced methylene blue photodegradation under the visible light where it has been demonstrated that the synergy between melon and SiO2 played an important role in it.
9:00 PM - Y8.39
Structure, Stability and Molecular Adsorption of Au-Rod/TiO2(110) Systems by First-Principles Calculations.
Hongqing Shi 1 , Masanori Kohyama 1 , Shingo Tanaka 1 , Seiji Takeda 2
1 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan, 2 Department of Physics, Osaka University, Toyonaka, Osaka, Japan
Show AbstractIn contrast to a long held view that gold is catalytically inert, Haruta found that gold nano-particles on metal oxides such as TiO2 exhibit strong catalytic activity such as low-temperature CO oxidation [1]. This finding has stimulated huge efforts to elucidate the mechanism. A lot of experimental reports indicate that the perimeter of Au particles on metal oxide surfaces plays a key role in the catalytic activity. Thus it is of great importance to investigate detailed atomic and electronic structures of the perimeter configurations of Au/metal-oxide interfaces and their chemical reactivity, theoretically and experimentally. In this study, we perform density-functional theory calculations of a Au rod deposited on a TiO2(110) surface with the relationship of Au(111)[011]//TiO2(110)[001] observed in a recent electron microscope observation [2]. The reason to deal with a Au rod is to examine realistic perimeter configurations by utilizing natural coincident periodicity along the Au[011] and TiO2[001] directions. We have examined Au-rod/TiO2(110) models with three kinds of interface stoichiometry [3]; namely stoichiometric interfaces, Ti-rich interfaces with bridging O atoms removed under a Au rod, and O-rich interfaces formed by digging a pit under a Au rod. We have also dealt with various rigid-body transformations for each model to examine possible atomic configurations of the perimeter region of the interface. By including the effect of temperature and oxygen partial pressure through the description of ab initio atomistic thermodynamics [4], we analyze the relative stability among various models with different stoichiometry. Then we analyze the atomic and electronic structures of the perimeter regions, consisting of Au-O or Au-Ti bonds, Au-edge or surface atoms and surface O or Ti atoms. Finally, molecular adsorption calculations are performed for several kinds of perimeter configurations with typical features so as to understand the catalytic activity. Acknowledgment: This study was supported by Grant-in-Aid for Specially Promoted Research (19001005). [1] M. Haruta, Catal. Today 36, 153 (1997); [2] T. Akita, K. Tanaka, M. Kohyama and M. Haruta, Surf. Interface Anal. 40, 1760 (2008); [3] K. Okazaki, Y. Morikawa, S. Tanaka, K. Tanaka and M. Kohyama, Phys. Rev. B 69, 235404 (2004); [4] K. Reuter and M. Scheffler, Phys. Rev. B 65, 035406 (2002).
9:00 PM - Y8.4
Great Enhancement of the Photocatalytic Activity of Pt Nanocrystals/One-dimensional Titanate Nanotubes Heterojunctions.
Liu Yueli 1 2 , Zhong Lei 1 , Li Hongquan 1 , Shu Wei 1 , Song Yanbao 1 , Chen Wen 1
1 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, and School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, Hubei, China, 2 INAC/SPrAM/LEMOH, CEA Grenoble, Grenoble France
Show AbstractDue to the unique features originating from the combination of a catalytically active of noble metal and a key semiconductor material,1 noble metal-loaded TiO2 composites have received much attention for decades, and they have been found to have wide applications for the purification and treatment of both contaminated air and water. Till now, several approaches for the synthesis of noble metal/TiO2 composites have been reported, including conventional impregnation and deposition-precipitation (DP) techniques, photodepositon, sputtering, colloidal methods, and so on.2 It is still a key problem to control the metal particle size, dispersion, and composition, etc.3 In the present work, we propose a process for synthesizing a novel layered-structure titanate (H2Ti5O11) nanotubes by a simple hydrothermal method, then Pt nanocrystals/titanate nanotubes heterojunctions are formed by chemical bath deposition (CBD) process, and it is found the heterojunctions have a great enhancement on the degradation of methyl orange solution. The as-grown titanate nanomaterials are proved to be hollow-centered H2Ti5O11 nanotubes (NTs) with smooth and flat surface. It is found that the Pt nanocrystals with diameters of 1-2 nm tightly attach on the surface of the titanate nanotubes by SEM and TEM images, and even enter their layers according to the slightly shift the XRD peaks. The combination of chemical states between the Pt nanocrystals and titanate nanotubes is charactered by X-ray photoelectron spectroscopy (XPS). Fourier transform infrared spectroscopy (FTIR) is used to identify the variation of chemical bond. The photocatalytic activity for the degradation of methyl orange solution is also studied at different ratio of the Pt precursor, which shows that the photocatalytic activity will increase with the increasing of the content ratio of the Pt precursor. The degradation ratio of the heterojunctions synthesized at the 8.2% of Pt precursor will increase to 100% in 300 min, as the heterojunctions will suppress the recombination of electron-hole pairs in titanate nanotubes, where the Pt particles act as electron traps aiding electron-hole separation.The Pt nanocrystals/titanate nanotubes heterojunctions could be easily in-situ formed by chemical bath deposition method, and the degradation of methyl orange solution could be greatly improved by the formation of the heterojunctions.Reference: (1) Valden, M.; Lai, X.; Goodman, D. W. Science 1998, 281, 1647. (2) Yan, W. F.; Shannon, M. M.; Pan, Z. W.; Steven, H. O.; Dai, S. J. Am. Chem. Soc. 2005, 127, 10480. (3) Corma, A.; Serna, P.; Garca, H. J. Am. Chem. Soc. 2007, 129, 6358.
9:00 PM - Y8.40
Single Step Morphology-controlled Synthesis of Silver Nanoparticles.
Vinodkumar Etacheri 1 2 , Reenamole Georgekutty 2 1 , Michael Seery 2 , Suresh Pillai 1
1 CREST, FOCAS Institute, Dublin Institute of Technology, Dublin Ireland, 2 School of Chemical and Pharmaceutical Sciences, Dublin Institute of Technology , Dublin Ireland
Show AbstractSilver nanoparticles have attracted wide applications in the field of photonics,[1] catalysis, medical research and Surface Enhanced Raman Spectroscopy (SERS).[2] The plasmon resonance phenomenon, antibacterial activity and high surface area make them highly interesting in the area of photonics, biological research and catalysis. Functional properties of these silver nanoparticles were found to be altered based on the shape and size. A large number of aqueous and non-aqueous methods were reported for the synthesis of silver nanoparticles having different size and shape.[3-5] Most of them use chemical and photochemical reduction or two step seed growing method in presence of a surfactant. For these preparations, reaction times can be long ranging from hours to days. There is still necessity of a simple single step method for the synthesis of silver nanoparticles having different morphologies and plasmon resonances. We are reporting an aqueous based rapid and surfactant free single step method for the synthesis of silver colloidal solutions having different colours (plasmon resonances). The current procedure was based on the reduction of silver ions by ascorbic acid in the presence of sodiumborohydride and trisodium citrate. The colour of sol (and thereby the size) was controlled by varying the concentration of only one reagent, namely ascorbic acid (Figure 1). TEM studies show that difference in colour and plasmon resonances is due to changes in morphology of the particles. Yellow sol contains only spherical silver nanoparticles (Figure 2). Well defined triangular nanoplates were observed for blue, green and grey sols. Colour of the sols depends on the size of nanoplates which again depends on the concentration of the reducing agent (ascorbic acid). Nanoplates having largest size (90 nm edge length) were observed in grey silver sol (Figure 3). Results suggested the in-situ formation of spherical silver seeds and their growth to triangular nanoplates. Studies of other parameters affecting the particle growth are underway.References[1].M. S. Hu, H. L. Chen, C. H. Shen, L. S. Hong, B. R. Huang, K. H. Chen and L. C. Chen, Nat. Mater., 2006, 5, 102–106. [2].S. E. J. Bell and N. M. S. Sirimuthu, J. Am. Chem. Soc., 2006, 128. 15580–15581.[3].M. Maillard, S. Giorgio and M.-P. Pileni, Adv. Mater., 2002, 14, 1084–1086.[4].X. Gu, C. Nie, Y. Lai and C. Lin, Mater. Chem. Phys., 2006, 96, 217–222. [5]. V. Bastys, I. Pastoriza-Santos, B. Rodriguez-Gonzalez, R. Vaisnoras and L. M. Liz-Marzan, Adv. Funct. Mater., 2006,16, 766–773.
9:00 PM - Y8.43
Surface Morphology of Pd3Fe(111) and the Effect of Adsorbed Oxygen on Surface Segregation.
Xiaofang Yang 1 , Bruce Koel 1
1 Department of Chemistry and Center for Advanced Materials and Nanotechnology, Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractPd/Fe alloy catalysts have attracted much attention in PEM fuel cell research because they have been found to be comparable to Pt electrocatalysts in oxygen reduction reaction (ORR) kinetics at the cathode. Much higher electrocatalytic activity is also found when these bimetallic nanoparticles act as a support of Pt or Pd monolayers.[1,2] However, the mechanism of enhancing ORR kinetics with this alloy is not well understood. Segregation in Pd3Fe(111) alloy, and in particular the influence of oxygen on this segregation has not been studied, but it is important for understanding catalytic activity and stability. In this study, surface segregation of Pd3Fe(111) and the role of oxygen in segregation are investigated by Low Energy Electron Diffraction (LEED), Low Energy Ion Scattering (LEIS), X-ray Photoelectron Spectroscopy (XPS), and Scanning Tunneling Microscopy (STM) under UHV conditions. Results from LEIS indicate that Pd starts to segregate on surface at 600 K and the highest coverage of Pd can be more than 0.9 monolayers at 1100 K. LEED gives clear and sharp (1x1) pattern with bulk atom registries. However, STM images reveal a complex surface at which the outermost layer is comprised of only 0.2 ML Pd adatoms and the second layer is still in alloy state. Multiple effects such as low surface energy of Pd atoms, strain relaxation and interaction between Pd and Fe, may be responsible for the formation of this unusual surface. Adsorption of oxygen reverses the segregation trend and causes Fe atoms to accumulate on the surface. It is also found that Fe at the surface is oxidized by oxygen. Besides, it is observed that dosing oxygen at different temperatures causes formation of well-organized surface structures, such as (7×7)R21.8 °structure at 700 K, both (7×7) R21.8 °and (√3 ×√3) R30° structures at 700 K~950K, and (√3 ×√3) R30° structure at temperature at 1000 K. Nanoclusters are formed when oxygen is dosed at lower temperatures (300K~500K). Such studies of segregation and oxidation of Fe in Pd/Fe alloy catalysts may help explain the origin of enhancing ORR kinetics for these alloys. References:[1]Zhang, J.; Vukmirovic, M. B.; Sasaki, K.; Nilekar, A. U.; Mavrikakis, M.; Adzic, R. R. Journal of the American Chemical Society 127, 12480 (2005). [2] Shao, M.H.; Sasaki, K.; Adzic, R. R. Journal of the American Chemical Society, 128, 3526 (2006).
9:00 PM - Y8.5
Au Nanoarchitechtures on the Tubular Support of Crystalline Anatase TiO2 for Enhanced Photocatalytic Activities.
Hyunchul Kim 1 , Hyunjun Yoo 1 , Changdeuck Bae 2 , Jooho Moon 2 , Hyunjung Shin 1
1 National Research Lab. for Nanotubular Structures of Oxides, Center for Materials and Processes of Self-Assembly, and School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of)
Show AbstractSurface electronic and interfacial structures of gold/titanium dioxide (Au/TiO2) heterojuctions in the nanometer scale are crucial for efficient generation of the excitons and enhanced photocatalytic activities. We fabricated two different kinds of Au/TiO2 heterojuctions at the nanometer scale. We employed TiO2 nanotubes (NTs) as a starting catalyst and/or catalytic support that have been prepared by template-directed atomic layer deposition (ALD) in a controlled manner. With this method, all the physical dimensions of the TiO2 NTs including wall thickness, inner and outer diameters, and length were precisely controlled at the sub-nanometer length scale. Upon surface treatment of TiO2 NTs, we were able to have deposits of Au nanoparticles (NPs) with 1-5 nm in diameter on the desired surfaces, i.e., inner and/or outer surfaces, by deposition-precipitation (DP) or photocatalytic deposition (PD) methods. We found that the areal density of the resulting Au NPs on the surfaces of TiO2 NTs was unprecedentedly high (more than two times), that is ascribed to the presence of the surface atomic step edges of TiO2 NTs. Enhanced photocatalytic activities of the resulting Au/TiO2 heterojuction nanostructures by comparing the characteristic times for the decomposition of methylene blue as a model pollutant have been studied. As Au dots on the TiO2 supports become smaller in diameter and higher in the areal density, the relatively shorter characteristic time for the decomposition was observed.Au nanowires (NWs) inside the TiO2 NTs as core/sheath 1D nanoarchitectures were synthesized photocatalytically in a controlled manner. Electrons photo-excited on the surfaces of TiO2 NTs by ultraviolet (UV) irradiation nucleated Au dots at the specific sites. Upon longer exposure to UV light, the Au dots were grown up into the Au NWs forming Au/TiO2 as core/sheath nanostructures. Au NWs were typically grown inside the TiO2 NTs with an orientation relationship of Au{111}∥TiO2{101}. The precise tailoring on the resulting Au features was detected in the optical measurements by exhibiting a series of the frequency shift of the surface plasmonic resonance peaks. Our novel growth methods on complex but controlled Au/TiO2 nanostructures should be beneficial for preparing improved photocatalysts and catalytic supports in a large quantity.
9:00 PM - Y8.6
Synthesis of Small Rhombioctahedron Shaped PtNi Nano-crystal Catalysts.
Hyon Chol Kang 1 , Se An Oh 2 , Do Young Noh 2
1 Department of Advanced Materials Engineering, Chosun University, Gwangju Korea (the Republic of), 2 Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractPt-Ni nano-crystal is a well-known electrochemical catalyst applicable in the electrode of low temperature direct methanol fuel cells. It has been reported that the Pt-Ni nano-crystal catalyst could enhance the electrochemical activity compared with that of Pt nano-crystal catalyst. To utilize such Pt-Ni nano-crystal catalyst, controlling the size and the crystal shape in the fabrication process of Pt-Ni nano-crystals on the carbon electrode are the critical issue to be addressed, since the reaction activity is strongly associated with the facet surfaces of Pt-Ni nano-crystal. In this presentation, we will discuss a new shape of Pt-Ni nano-crystals, i.e. small rhombicuboctahedron, never before been reported in Pt-Ni system. The Pt-Ni nano-crystals can be simply synthesized by thermal annealing of Pt/Ni bilayer on single crystal sapphire(0001) substrate. During annealing at a temperature of 850oC, top Pt layer is intermixed with Ni forming a Pt-Ni alloy layer. Because of large difference of surface energy between substrate sapphire and Pt-Ni layer, many small holes are generated and grown on its surface to reduce the surface energy, resulted in the formation of discontinuous Pt-Ni islands with round shape. As the annealing proceeded further, the Pt-Ni islands are transformed into faceted nano-crystals. The small rhombicuboctahederon with eighteen (001) and eight (111) facets is dominant, although cuboctahedron and great rhombicuboctahedron shapes are negligibly observed. Averaged lateral size is about 200 nm and the height is about 120 nm that can be adjustable by varying the thickness of Pt/Ni bilayer.
9:00 PM - Y8.7
Shape Control of Platinum Array Catalyst.
Hakim Iddir 1 , Peter Zapol 1 , Vladimir Komanicky 2 , Hoydoo You 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 , Institute of Experimental Physics, Kosice Slovakia
Show AbstractParticle size, shape, surface structure, and the metal-support interfaces are all expected to have a great influence on catalytic activity and selectivity. Therefore, these factors need to be optimized and controlled. Shape evolution of supported platinum nanoparticle arrays on SrTiO3 (001) under oxygen environment is studied using a combination of first-principles thermodynamic calculations based on density functional theory, and state of the art nanofabrication techniques coupled with synchrotron x-ray scattering, SEM and AFM characterization tools. Facet areas were found to change with oxygen pressure, e.g. (100)-(hex) surfaces are stable at low oxygen pressures and (110)-(2x1) missing row reconstructed facets grow wider at higher oxygen pressures. High-index (311) and (210) facets were found to appear at intermediate pressures. The fabricated nanoparticle array catalysts have shown a unique enhancement of oxygen reduction reaction activity. The shape of platinum nanoparticles can be controlled by the substrate orientation, annealing conditions and also by applied electrochemical potential.
Symposium Organizers
Sheng Dai Oak Ridge National Laboratory
Harold H. Kung Northwestern University
Jun Liu Pacific Northwest National Laboratory
Chung-Yuan Mou National Taiwan University
Y9
Session Chairs
Chung-Yuan Mou
Donghai Wang
Thursday AM, December 03, 2009
Room 311 (Hynes)
9:30 AM - **Y9.1
Oxynitrids as Photocatalysts for Overall Water Splitting.
Kazunari Domen 1
1 , The University of Tokyo, Tokyo Japan
Show AbstractHydrogen production on semiconductor photocatalyst by water splitting is an ideal method to produce clean and recyclable energy carrier. Nowadays, the study to efficiently decompose water under ultraviolet light irradiation using wide gap metal oxides has been well established and the current research target has been directed toward visible light photocatalysis. We have developed some metal nitrides and oxynitrides as photocatalyst to utilize visible light. Bandgap narrowing occurs for metal (oxy)nitrides compared to the corresponding metal oxides. The valence band maximum shifts toward the negative by substituting nitrogen for oxygen owing to the difference in electronic potential between N2p and O2p orbitals. Several transition metal oxynitrides based on Ti 4+ , Ta 5+ or Nb 5+ were found to have absorption bands covering wide range of visible light. These oxynitrides evolved H 2 and O 2 via band gap excitation without noticeable photodegradation of catalyst in the presence of proper sacrificial reagents 1) . However, overall water splitting has not yet been achieved. Visible light induced overall water splitting was achieved by a typical metal oxynitride consisting of Zn-Ga as a first example2). In this material, the structure was found to be a solid solution of GaN and ZnO generally formulated as (Ga 1-x Z x )(N 1-x O x ). The absorption edge of this material extends to visible region (- 480 nm) although both GaN and ZnO absorb only ultraviolet light essentially. This indicates that band gap narrowing occurs for the solid solution owing to the new electronic structure formed by mixing GaN and ZnO. Some oxynitride photocatalytic materials are applicable to visible light driven photoelectrochemical water splitting. LaTiO 2 N is a promising candidate of photoelectrode for water decomposition without expernal bias due to a suitable bandgap position3) .Visible light drivem water splitting using photocatalysts and photoelectrodes are enhanced by various approaches. Details will be reported in presentation.[1] Hitoki, G., Takata, T., Kondo, J. N., Hara, M., Kobayashi, H., Domen, K., Electrochem., 2002, 70: 463.[2] Maeda, K., Takata, T., Hara, M., Saito, N., Inoue, Y., Kobayashi, H., Domen, K., J. Am. Chem. Soc., 2005, 127: 8286.[3] Le Paven-Thivet, C., Ishikawa, A., Ziani, A., Le Gendre, L., Yoshida, M., Kubota, J., Tessier, F., Domen, K., J. Phys. Chem. C 2009, 113: 6156
10:00 AM - Y9.2
Influence of BaTiO3 Substrates on the Photochemical Properties of Thin Titania Films.
Nina Burbure 1 , Paul Salvador 1 , Gregory Rohrer 1
1 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThe ability of titania to photochemically split water to produce hydrogen is limited, in part, by the recombination of charge carriers and the back reaction of reduced and oxidized intermediates. Ferroelectric materials with permanent dipoles have been shown to separate charge carriers and the reduction and oxidation products of photochemical reactions. Titania/BaTiO3 heterostructures have been investigated with the idea that the dipolar fields from the ferroelectric substrate will separate carriers in the film. Titania films have been deposited on BaTiO3 substrates by pulsed laser deposition. Films with thicknesses in the range of 10 nm to 100 nm were deposited at 700 °C on substrates with a variety of orientations. Electron backscatter diffraction was used to determine both the substrate and the film orientation. Anatase with the (001) orientation forms on BaTiO3 (100), rutile with the (110) orientation forms on BaTiO3 (110), and rutile with the (100) orientation forms on BaTiO3 (111). Both the substrates and the films were used to photochemically reduce Ag+ and oxidize Pb2+ from aqueous solutions. On the substrates, the products of each of these reactions (Ag and PbO2) deposit in patterns that correlate to the underlying domain structure, with silver forming on positive domains (domains with the polarization vector pointing toward the surface) and PbO2 on negative domains. When same reactions are conducted on films with thicknesses of less than 50 nm, the same product form in patterns above the same domains. For films with thicknesses greater than 100 nm, the reactivity is more spatially uniform and comparable to bulk titania. For all of the orientations, the thinnest films have reactivities equal to or greater than the bulk-like films, suggesting that the charge separating characteristics of the substrate have the potential to increase the reactivity of titania. The observations are discussed in terms of a model for the positions of the electronic bands in the heterostructure.
10:15 AM - Y9.3
CdTe:Hydrogenase Complexes Capable of Light-driven Hydrogen Production.
Katherine Brown 1 , Smita Dayal 1 , Garry Rumbles 1 , Maria Ghirardi 1 , Paul King 1
1 , National Renewable Energy Lab, Golden, Colorado, United States
Show AbstractLight driven production of hydrogen is an area of interest in developing renewable, green energy technologies. Nature has evolved highly efficient enzymes, hydrogenases, which catalyze the generation of hydrogen gas (H2). In photosynthetic, H2 producing microbes, substrate electrons are generated by photosystems that couple light capture to charge-separation, and donated to ferredoxins that mediate transfer of the reducing electrons to hydrogenase. We are investigating the properties of bio-nano hybrid systems in which the photosynthetic light capture and charge transfer biomachinery are replaced by a semiconducting nanomaterial that is in contact with the biological catalyst hydrogenase. Such a system allows for direct transfer of photo-generated electrons to a surface bound hydrogenase for the production of H2. We report the synthesis of soluble molecular complexes between 2.7nm CdTe nanocrystals and the [FeFe]-hydrogenase I from Clostridium acetobutylicum (Ca1). Spontaneous CdTe:Ca1 complex formation in solution is shown by an increase in the photoluminescence signal of the CdTe, consistent with published reports of nanocrystals-protein complex formation[1, 2]. Further, polyacrylamide gel electrophoresis shows the CdTe:Ca1 complexes are stable, and form in a distribution of discrete stoichiometric complexes. In situ activity staining demonstrates that the hydrogenase retains activity when associated with the CdTe nanocrystal. Electron transfer from CdTe to species in solution was demonstrated by the reduction of methyl viologen (MV), which serves as a colorimetric indicator of electron transfer[3, 4]. Band-edge redox potentials of the CdTe nanocrystals were estimated by fitting the Nernst equation for MV, which has an Em near the H/H2 couple. The result demonstrates the suitability of CdTe nanocrystals as photocollecting, electron transfer partners for Ca1. Under illumination, the CdTe:Ca1 complexes generate H2, with an average incident photon conversion efficiency of 0.5%. The conversion efficiency varies depending on the CdTe:Ca1 molar ratio, with a maximum at a ratio of 1:2 (CdTe:Ca1). These results demonstrate the suitability of CdTe:Ca1 complexes to act as model systems for the further study of bio-nano hybrids for light-driven hydrogen production. 1.Lin, Z., et al., Analytical Biochemistry, 2003. 319(2): p. 239-243.2.Wang, Q., et al., The Journal of Physical Chemistry B, 2006. 110(34): p. 16860-16866.3.Dimitrijevic, N.M., et al., The Journal of Physical Chemistry, 1984. 88(19): p. 4278-4283.4.Duonghong, D., J. Ramsden, and M. Graetzel, Journal of the American Chemical Society, 1982. 104(11): p. 2977-2985.
10:30 AM - Y9.4
Photocatalytic Behavior of PbS Quantum Dot/TiO2 Nanotube Composites.
Chalita Ratanatawanate 1 , Khiem Vu 1 , Kenneth Balkus 1
1 chemistry, University of Texas at Dallas, Richardson, Texas, United States
Show AbstractThere is growing interest in TiO2 nanostructures for photoconversion processes. High surface area TiO2 nanotubes (TNTs) with 3-5 nm inner diameters were prepared by a hydrothermal process. PbS quantum dots (PbS QDs) were attached to TiO2 nanotubes on both the inside and outside surfaces of the nanotubes by using a bifunctional linker. The PbS QDs with diameters of 4-5 nm were controlled by adjusting the concentration of a linking agent. PbS QDs can be placed only inside the nanotubes by first blocking the outer surface of the TNTs with the double-chain cationic surfactant. The photocatalytic activities and stability of PbS/TiO2 nanotubes were evaluated for the photodegradation of organic dyes, especially cationic dyes and phenols. The results suggested that the quantum dots enhance the activity and expand the usable portion of the solar spectrum.
10:45 AM - Y9.5
Control of Particle Size and Thin Film Surface Morphology Using Femtosecond Pulsed Laser Deposition for Photocatalyst and Other Catalyst Applications.
Makoto Murakami 1 , Bing Liu 1 , Zhendong Hu 1 , Yong Che 1
1 , IMRA America, Inc, Ann Arbor, Michigan, United States
Show AbstractFor photocatalyst and other catalyst applications, controlling their particle size and surface morphology is one of the most important approaches to optimize the catalyst performances. In this presentation, we introduce a novel method to control the particle size and the surface morphology, and a method of pulsed laser deposition (PLD) using a femtosecond pulsed laser with burst-mode, which is a multi-pulse mode of selected number of pulses with very short time separation (20 ns) in between the pulses [1]. This method enables controllability for thin-film morphologies, ranging from nanoparticle aggregates to epitaxial thin films with completely droplet-free and atomically smooth surfaces. TiO2, one of the promising photocatalyst, is used as a demonstration material in this work. A fiber based femtosecond laser (FCPA μJewel™ D-1000 laser developed by IMRA America, Inc.) is used for generating burst-mode laser pulses. The number of burst-mode pulses is selectively controlled from 1 to 20, and the repetition rate of the burst is also tunable in the range of 0.1 – 5 MHz. A TiO2 ceramic target placed in vacuum chamber is ablated with different number of pulses. When more number of pulses is used for the ablation (typically more than 10 pulses), atomically smooth thin films free of droplets and clusters are obtained. The satisfactory film morphology and quality by using the burst-mode ablation are further demonstrated for epitaxial growth of TiO2 thin film on LaAlO3 (001) substrate. Root mean square of a 70 nm thick TiO2 thin film with 3 x 3 µm2 scan is < 0.22 nm confirmed by AFM, and full width half maximum (FWHM) of rocking curve of anatase (004) peak in XRD is 0.11 degree. While by decreasing the number of bust-pulses and/or increasing pulse energy for the ablations, rough films of nanoparticle aggregates are obtained with increasing particle size. The resultant TiO2 nanoparticle aggregates, even deposited at room temperature, exhibit crystalline structure and corresponding photocatalytic effect. Since crystalline TiO2 thin films can be grown at room temperature, organic films can also be used as substrates for photocatalyst coating. Morphology control of thin films is further demonstrated for many other materials such as metals (Au, Pt, Co etc.) and metal oxide (SnO2, Mn3O4, Fe3O4, CoO, HfO2, Cr2O3, SiO2, BaTiO3 etc.). The details of the method and its potential applications in the field of catalysis will be discussed.[1] M. Murakami et al. Appl. Phys. Express, 2 042501 (2009)
11:30 AM - **Y9.6
Ultrahigh Resolution NMR and TEM Studies of Poorly Crystalline γ–Al2O3 Surfaces as Support Materials for Next Generation Vehicle Emission Control Catalysts.
Ja Hun Kwak 1 , Jianzhi Hu 1 , Donghai Mei 1 , Do Heui Kim 1 , Janos Szanyi 1 , Larry Allard 2 , Chuck Peden 1
1 Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, Washington, United States, 2 High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstractγ-alumina, one of the metastable ‘transition’ alumina structural polymorphs, is an important catalytic material both as an active phase and as a support for other catalytically active phases, with widespread applications ranging from petroleum refining to automotive emission control. As such, the bulk and surface structure of γ-alumina, and its formation and thermal stability have been and continue to be the subject of a considerable amount of research. However, due to the low crystallinity and very fine particle size of γ-alumina, it is very difficult to apply well-established analytical techniques for determining its surface structures. Of particular importance for understanding the catalytic properties of γ-alumina, relating its surface structure to the origin of Lewis and Brönsted acidity has been of considerable interest and has been studied by solid state NMR and FTIR spectroscopies, and most recently by theoretical calculations. In this presentation, we describe recent studies using ultra-high resolution NMR spectroscopy as an especially useful probe of the γ-alumina surface structure, and its relevance to catalytic behavior. In particular, we coorelate the NMR spectra with measurements of the adsorption and reaction of catalytically active phases such as BaO and Pt. In this way, we demonstrate a strong dependence of the anchoring of these catalytic phases on the presence of specific 5-coordinate Al3+ ions. Ultrahigh resolution transmission electron microscopy (HR-STEM) images of these materials provide strong support for these conclusions. To investigate the interaction of a catalytically active phase with penta-coordinated Al3+ sites on the alumina surface, a series of BaO/γ-Al2O3 samples with low BaO loadings (0.5, 1, and 2 %) were prepared. 27Al MAS NMR spectra were acquired for these samples along with a spectrum of BaO-free γ-alumina. The integrated intensity of a 23 ppm peak due to penta-coordinated Al3+ ions as a function of BaO loading demonstrates that the intensity of the peak at 23 ppm decreases linearly with increasing BaO loading. These results strongly support a conclusion that BaO, formed by the decomposition of Ba(NO3)2, interacts with the alumina by preferentially anchoring to these penta-coordinated Al3+ surface sites. Similar behavior has been observed for the important catalytic material Pt. At low Pt loadings (<1 wt%), Pt is atomically dispersed on the support surface (Pt/Al3+penta=1). When the loading of Pt exceeds the number of Al3+penta sites, two dimensional PtO rafts form as evidenced by HR STEM measurements. DFT calculations provide further confirmation for the energetic feasibility of the formation of these two dimensional rafts as well as for their energetically most stable overlayer structure.
12:00 PM - Y9.7
Synthesis and Catalytic Properties of Microemulsion-Derived Ceria Nanoparticles.
Christian Schrage 1 , Stefan Kaskel 1 , Emanuel Kockrick 1 , Dorin Geiger 2 , Anett Grigas 1
1 , Dresden University of Technology, Dresden Germany, 2 Triebenberg Laboratory for HRTEM and Electron Holography, Department for Structure Physics, Department of Inorganic Chemistry, Dresden University of Technology, Dresden Germany
Show AbstractNanostructured inorganic particles are promising systems asoxidation catalysts due to the high surface to volume ratio. Especially, nanoscale ceria containing systems are a very attractive three-way catalyst systems for soot combustion reactions.The synthesis of cerium dioxide nanoparticles using an inverse microemulsion technique and precipitation method was investigated. Cerium hydroxide nanoparticles were synthesized by adding diluted ammonia to n-heptane–surfactant–cerium nitrate system. The micelle and particle size in the range of 5–12nm were controlled by varying the molar water to surfactant ratio and analyzed by dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM). Cerium hydroxide nanoparticles were isolated and subsequently treated at 100–600 °C to obtain nanoscale ceria. Crystallite sizes of ceria in the range of 6–16nm were estimated by Scherrer analysis by X-ray diffraction (XRD) and HRTEM. The catalytic activity of particles annealed at 400 and 600 °C in soot combustion reactions was characterized by temperature-programmedoxidation (TPO) indicating a size-dependant activity. Crystallite sizes and catalytic stability of elevated ceria systems were tested in second combustion cycles.
12:15 PM - Y9.8
Preferential Location of Pt in Ternary DeNOx Catalysts.
Robert Buechel 1 , Alfons Baiker 2 , Sotiris E. Pratsinis 1
1 D-MAVT, ETH Zurich, Zurich Switzerland, 2 D-CHAB, ETH Zurich, Zurich Switzerland
Show AbstractFuel lean combustion engines can reach higher fuel efficiency, however, NOx reduction is more challenging. An ideal NOx storage-reduction (NSR) catalyst can store effluent NOx in the form of metal nitrates under fuel lean conditions and reduce them to N2 in a subsequent short fuel rich period [1]. Such catalysts typically contain several elements belonging to one of the following three main functions: NOx storage material to absorb volatile NOx (e.g. Ba, K), support (e.g. Al2O3, CeO2) to keep the material well dispersed even at high temperatures and noble metal (e.g. Pt, Pd) to catalyze the reactions at temperatures between 300-400 °C [2]. The location of the noble metal was found to have a major influence on the catalytic activity because of the support effect and the spillover distance to the storage material (e.g. BaCO3) [3]. Here we demonstrate how Pt can be deposited selectively on Al2O3 (support) or BaCO3 (storage material) with a two-nozzle Flame Spray (FSP) setup and illustrate its effect on catalytic performance. The different Pt sites were elucidated by electron microscopy techniques. NSR behavior of these catalysts as well as of sequential setups of catalytic beds was investigated in a microreactor by switching between lean and rich conditions. The preferential deposition of platinum on the alumina support or Ba storage component corroborate that location of the Pt defines the performance of NSR catalysts. Various support elements can limit NSR activity, however, Pt directly deposited on BaCO3 increases the regeneration of the catalysts and is therefore better for long run experiments.References:[1]W.S. Epling, L.E. Campbell, A. Yezerets, N.W. Currier, J.E. Parks, Cat. Rev. - Sci. Eng. 46 (2004) 163-245.[2]M.O. Symalla, A. Drochner, H. Vogel, R. Büchel, S.E. Pratsinis, A. Baiker, Appl. Catal., B 89 (2009) 41-48.[3]R. Büchel, R. Strobel, F. Krumeich, A. Baiker, S.E. Pratsinis, J. Catal. 261 (2009) 201-207.
12:30 PM - Y9.9
Atoms At Work.
Christian Kisielowski 1 , Lars Hansen 2 , Michael Brorson 2 , Stig Helveg 2
1 National Center for Electron Microscopy and Helios SERC, Lawrence Berkeley National Laboratory, Berkeley , California, United States, 2 , Haldor Topsøe A/S, Kgs. Lyngby, DK, Denmark
Show AbstractIn recent years electron microscopy made significant progress because of advancements in electron optics [1]. In fact single atom detection across the Periodic Table of Elements became a reality because of extraordinary low noise levels [2]. Parallel developments of environmental transmission electron microscopy (ETEM) made available a powerful tool for in situ studies of heterogeneous catalysts for e.g. environmental protection, energy conversion and chemical production [3]. It is desirable to take advantage of these emerging technologies to study catalytic processes on a single atom level since it is now possible to image single light and heavy atoms simultaneously. In this contribution we demonstrate that a refined sample preparation in combination with advanced imaging tools allows studying the dynamics of atoms in graphene or graphite substrates as well as the dynamic attachment of heavy atoms to edge atoms of such substrates. [1] http://ncem.lbl.gov/team/TEAMpage/TEAMpage.html[2] C. Kisielowski, B. Freitag, M. Bischoff, et al. Microscopy and Microanalysis 14 (2008) 454[3] S. Helveg et al., Nature 427, 426 (2004).
12:45 PM - Y9.10
Theoretical and Experimental Studies of Rh and Pd on a CeO2(111) Surface.
Obiefune Ezekoye 1 , Bai-Hai Li 2 , George Graham 1 , Liang Chen 2 , Xiaoqing Pan 1
1 Materials Science and Engineering, The University of Michigan, Ann Arbor, Michigan, United States, 2 , Ningbo Institute of Materials Technology and Engineering, Ningbo China
Show AbstractPd and Rh supported on ceria-based oxides are critical components in modern automotive three way catalysts (TWCs). In TWCs, there can be significant, sometimes damaging, interactions between the metal and oxide supports. Cross sectional high resolution transmission electron microscopy (HRTEM) is a useful tool for studying these interactions. For example, this technique yields a visual image of the particle cross section, which can be used in calculating the thermodynamic properties of the interface and observing differences in metal-support interactions. For the present experiments, thin CeO2(111) films were grown on YSZ (111) substrates using pulsed laser deposition. A monolayer-equivalent of either Pd or Rh was deposited onto these films in an ultrahigh vacuum deposition chamber. Subsequently, these samples underwent calcinations at 600°C. Cross sectional analysis of the metal-ceria interface was performed using HRTEM. In addition to experimental observations, spin polarized DFT calculations were performed using the Vienna ab initio simulation package (VASP). Molecular dynamics (MD) simulations were then used to model the agglomeration dynamics of Pd and Rh on ceria surfaces. The overall objective of this work is to combine direct experimental observations, first-principles calculations, and MD simulation to investigate the coarsening behavior of Pd and Rh particles on the CeO2(111) surface.
Thursday PM, December 03, 2009
Room 311 (Hynes)
2:30 PM - **Y10.1
Shape Effect on the Catalytic Properties of Nanoscale Au-ZnO.
M. Boucher 1 , R. Si 1 , Maria Flytzani-Stephanopoulos 1
1 , Tufts University, Medford, Massachusetts, United States
Show AbstractGold supported on metal oxides has been studied recently as a catalyst for hydrogen producing reactions such as the water-gas shift (WGS) and methanol steam reforming (MSR). There is ongoing debate as to whether the activity of nanogold depends mainly on its particle size, or whether the interaction with the oxide support (CeO2, FeOx, ZnO) at the interface creates the active sites. Gold-zinc oxide (Au-ZnO) is a particularly appealing catalyst not only due to its good activity and stability for low temperature oxidation reactions, but also owing to the interesting structural properties of ZnO. Furthermore, the simplicity of the shape controlled synthesis of 1-D single crystal ZnO nanostructures, makes it a promising candidate for examining the structural effect of the Au-support interaction on its catalytic properties. Here, we first report on a composite Au-ZnO material prepared by depositing Au nanoparticles via colloidal suspension on controlled, nanoscale ZnO shapes/crystal planes. We show that the activity and selectivity of Au-ZnO can be tuned for low- temperature applications by controlling the crystal structure of ZnO.
3:00 PM - Y10.2
Oxidation of Ethanol Promoted by Gold Nanoparticles: Reactivity Control and Mechanistic Studies.
Xiaoying Liu 1 , Bingjun Xu 1 , Robert Madix 2 , Cynthia Friend 1 2
1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractGold-based catalysis has received tremendous interest since the discovery that gold nanoparticles supported on metal oxides promote the catalytic oxidation of CO and alkenes at low temperature. More recently, the use of gold catalysts to promote the aerobic oxidation of alcohols has become the center of attention, affording the possibility of producing carbonyl derivatives through energy-efficient processes. Recent studies have shown that gold nanoparticles supported on inert carbon substrates or without support materials are likewise active. In this work, we present a detailed study of ethanol oxidation over oxygen-containing gold nanoparticles that are prepared on the Au(111) surface to reveal the intrinsic characteristics of gold. Both the particle size dependency of the surface reactivity and the reaction mechanism are discussed.We show that the reactivity for the oxidation of ethanol depends on the local bonding, particle size, and degree of order that are controlled by the temperature for oxygen deposition using ozone. This process forms O-containing gold nanoparticles on the surface. On small, disordered particles, 80% of which show diameters of ~ 2 nm, oxygen is bound in sites with local 3-fold coordination, based on measured vibrational energies. Oxygen on these small disordered nanoparticles, formed by ozone decomposition on Au(111) at 200 K, is highly reactive and yields ethyl acetate, acetic acid, ketene, and CO2. In contrast, atomic oxygen present in ordered two-dimensional islands with diameters > 5nm formed by exposure to ozone at 400 K is relatively unreactive and only produces very small amount of ethyl acetate, ~ 16% of that for the surface prepared at 200 K. These results indicate that local bonding of O is an important factor to consider in understanding the effect of particle size in gold-based catalytic reactions.We also establish the mechanism for the extremely facile transformation of ethanol to ethyl acetate below room temperature, in competition with secondary oxidation to acetic acid, ketene, and CO2. We clearly demonstrate that the oxidation of ethanol on oxygen-containing gold nanoparticles strongly parallels the reaction patterns over gold supported on TiO2 or MgAl2O4 under high-pressure, aqueous phase conditions. Moreover, our results define the general mechanistic framework for catalytic oxidation of alcohols on supported catalysts and specifically show the self-coupling pathway to form the ester involves two key intermediates—ethoxy and acetaldehyde. The surface-mediated nucleophilic attack of the aldehydic carbon by alkoxy is generally applicable to the coupling between two alcohols and between alcohol and aldehyde on gold.
3:15 PM - Y10.3
Stability of Supported Gold Nanoparticles.
Timothy Turba 1 , Whitney Patterson 1 , Grant Norton 1 , David McIlroy 2
1 , Washington State University, Pullman, Washington, United States, 2 , University of Idaho, Moscow, Idaho, United States
Show AbstractGold nanoparticles have applications ranging from catalysts for low temperature oxidation of CO, to solar energy capture in the infrared, to sensitive gas sensors. For all these applications, particle size and shape are critical. Although it is the least reactive bulk metal, gold nanoparticles are extremely active and selective in various catalytic reactions when under 5 nm in diameter. Because many reactions, even involving nanoparticles run at elevated temperatures, it is imperative to understand the thermal stability of the particles and the extent to which ripening may occur. In addition to their reactivity, gold nanoparticles absorb light through surface plasmon resonance, which can be tuned to different wavelengths by controlling particle size and shape. Thus, if nanoparticle size changes can be understood and strictly controlled, it may be possible to create an array of gold nanoparticles that absorb the full solar spectrum. Utilizing such an array as a solar cell could lead to increases in efficiency over present photovoltaic devices. Supported gold nanoparticles have also been shown to make sensitive gas sensors. The depletion layer created by the nanoparticle gold on a semiconductor surface allows for detection of reactive gases like methane. Thermally induced changes in particle size could significantly affect the behavior and performance of these types of devices. An additional factor that is becoming increasing important is the nature of the substrate surface on which the nanoparticles are supported and electronic interactions between substrate and particle. For example, gold nanoparticles formed on GaN nanowires ripen noticeably in size and shape at temperatures as low as 150°C through particle migration and coalescence rather than atom diffusion. However, gold nanoparticles formed on silica nanosprings appear to be significantly more stable. In this presentation, the thermally-induced ripening of gold nanoparticles formed on a number of nanostructured substrates by plasma-enhanced chemical vapor deposition will be described. In particular, the mechanisms for ripening and the associated size and shape changes will be discussed. The eventual goal of this work is to be able to predict and control these variables in a useful way.
3:30 PM - Y10.4
Carbon Monoxide-Assisted Catalytic Epoxidation of Olefins over Supported Au Catalysts.
Jian Jiang 1 , Mayfair Kung 1 , Harold Kung 1
1 Chemical and Biological Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractEpoxidation is an important industrial reaction to prepare precursors for some important polymers. Except for ethylene, epoxidation of olefins often uses organic peroxides that are expensive and generate wasteful byproducts. It is highly desirable to be able to synthesize epoxides using molecular oxygen.Supported Au nanoparticles have been found to be capable of producing hydrogen peroxide during aqueous phase CO oxidation. Thus, this system could be used for epoxidation using molecular oxygen. Indeed, a Au/TiO2 catalyst that is active for CO oxidation in the aqueous phase, when present together with a TS-1 catalyst, produces epoxide from butene. When the consumptions of oxygen and CO were determined using the same catalyst using the same reaction mixture, excess oxygen consumption relative to that used for stoichiometric oxidation of CO was observed only when the catalyst was in the liquid phase, and it can be maintained only when butene is also in the reaction mixture. In the absence of butene, hydrogen peroxide formation could be detected in the liquid, but its concentration reached a maximum after a few hours when there was no more excess consumption of oxygen. In the presence of butene, however, butene epoxide was detected both in the liquid and in the vapor exiting the reactor. The formation of butene epoxide in the liquid phase was an order of magnitude faster using the binary catalytic system Au/TiO2 and TS-1 than Au/TiO2 alone. The efficiency of epoxidation was quite high. In terms of oxygen consumption selectivity, between 10 to 50% of the oxygen is consumed productively to form epoxide, depending on the catalyst and the reaction condition.
3:45 PM - Y10.5
Reaction Mechanisms for the CO Oxidation on Au/CeO2 Catalysts.
Matteo Farnesi Camellone 1 , Stefano Fabris 1
1 Theory@Elettra group, INFM-CNR DEMOCRITOS National Simulation Center, Trieste, 0, Italy
Show AbstractDensity functional theory calculations that account for the on-site Coulomb interaction via a Hubbard term (DFT+U) reveal the mechanisms for the oxidation of CO catalyzed by isolated Au atoms as well as small clusters in Au/CeO2 catalysts. Ceria (111) surfaces containing positively charged Au ions, either as supported Au+ adatoms or as substitutional Au3+ ions, are shown to activate molecular CO and to catalyze its oxidation to CO2. In the case of supported single Au+ adatoms, the limiting rate for the CO oxidation is determined by the adsorbate spillover from the adatom to the oxide support. The reaction then proceeds with the CO oxidation via lattice oxygen and O vacancy formation. These vacancies are shown to readily attract the supported Au+ adatoms and to turn them into negatively charged Auδ- adspecies that deactivate the catalyst preventing further CO adsorption. Substitutional Au3+ ions dispersed into the ceria lattice can instead sustain a full catalytic cycle consisting of three individual steps maintaining their activity along the reaction process. The interplay between the reversible Ce4+/Ce3+ and Au3+/Au+ reductions underpins the high catalytic activity of dispersed Au atoms into the ceria substrate, although surface thermodynamics show that the stability of these systems is an important issue. It is shown that the positive oxidation state of the substitutional Au ions is retained along the catalytic cycle thus preventing the deactivation of AuxCe1-xO2 catalysts in operation conditions. Finally, although a single Au+ adatom bound to an O vacancy is shown to be inactive towards CO oxidation, the calculations predict that the reactivity of gold nanoparticles nucleated at O vacancies can be recovered for cluster sizes as small as Au2.
4:30 PM - Y10.6
Mesoporous Crystalline Metal Oxide Supported Au Catalysts.
Donghai Wang 1 , Zhen Ma 2 , Daiwon Choi 1 , Zimin Nie 1 , Zhenguo Yang 1 , Sheng Dai 2 , Jun Liu 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractSelf-assembled nanoporous materials with high surface areas and crystalline framework and open pore channels have great potential for catalysis. However, preparation of stable, high quality crystalline nanoporous materials remains difficult for materials such as metal oxide. Typical self-assembled nanoporous metal oxide is made of amorphous, semicrystalline or nanocrystalline phase. High temperature treatments to remove surfactants result in collapse of the nanopores. Here we discuss a novel low temperature approach with surfactant assisted crystallization and self-assembly to prepare high surface area, highly crystalline nanoporous metal oxides for Au catalysis applications. Metal oxide-supported gold nanoparticles are an important new class of catalysts for low temperature oxidation and water shift reaction. The gold nanoparticles supported on highly crystalline mesoporous metal oxide (TiO2 and CeO2) show high reactivity and on-stream stability towards low-temperature CO oxidation and water shift reaction by stabilizing gold nanoparticles against sintering within the three-dimensional nanostructures. Understanding the roles of nanostructure in these applications can provide insights into design of new catalysts.
4:45 PM - Y10.7
Structures and CO Oxidation Activities of Size-selected Gold Nanoparticles in Titania-coated Silica Aerogels.
Yutaka Tai 1 , Wataru Yamaguchi 1 , Koji Tajiri 1 , Hiroyuki Kageyama 2
1 Mater. Res. Inst. for Sustainable Development, Natl. Inst. Adv. Ind. Sci. Tech. (AIST), Nagoya Japan, 2 Res. Inst. for Ubiquitous Energy Devices, Natl. Inst. Adv. Ind. Sci. Tech. (AIST), Ikeda Japan
Show AbstractWe have prepared Au/Titania-coated silica aerogel catalysts from Au nanoparticles (AuNPs) having well-regulated sizes in the range 1.4-6.4 nm, through heat-treatment of thiol-capped AuNPs, size-separation through fractional precipitation, and adsorption of the AuNPs on the support in a nonpolar solvent. The Au particle size was preserved during calcination of the catalyst samples at 673 K and subsequent CO oxidation. The turnover frequency for CO oxidation of the catalysts changed drastically when their sizes varied from 4 to 5 nm, but it did not change appreciably in other size regions. X-ray absorption spectroscopy and X-ray diffraction measurements revealed that lattice contraction and structural changes become prominent at Au diameters of less than 4-5 nm. Thus, the structural changes that occurred in the AuNPs in this diameter region are consistent with the enhanced catalytic activity.