3:30 PM - *ES12.02.05
Engineering Exsolution-Promoted Perovskites for Efficient Thermochemical Syngas Production
Jennifer Rupp1,Alfonso Carrillo1,Kunjoong Kim1,Zachary Hood1
Massachusetts Institute of Technology1
Perovskites have shown great promise as efficient redox materials for solar-to-fuel production due to higher oxygen exchange capacity, which in turn results in higher fuels yields compared to state-of-the-art ceria. Additionally, perovskites can be easily modified through extrinsic doping leading to new compositions with altered kinetics, redox capacity and reduction temperatures, which positively impacts the overall syngas production.1 Alternatively, reduction temperatures can be lowered down by using methane as reductive gas, which has the additional benefit of leading to syngas production during the reduction half-cycle by the so-called methane partial oxidation2, in which oxygen lattice of the perovskite reacts with methane producing H2 and CO in a 2:1 ratio, ideal for further syngas processing into liquid fuels. In the second step, the reduced perovskite can be reoxidized by CO2, H2O or a mixture thereof, resulting in the production of fuel for both steps, which increases the overall solar-to-fuel process efficiency. This technology also known as solar chemical looping reforming, requires materials with high oxygen capacity and fast redox kinetics. Traditionally, cermets based on ceria or perovskites composed by a metallic catalyst impregnated onto the oxide surface have been explored for improving reaction rates, gas conversion and syngas selectivity2. However, high temperatures can lead to metal catalyst agglomeration and coarsening, decreasing its chemical activity and cermet stability. Motivated by this fact, we have explored processing of perovskite-cermet structures through the exsolution method as an alternative to impregnation, which was successfully demonstrated to control the catalysis e.g. for (La,Sr)(Ti,Ni)O3 solid oxide fuel cell anodes.3,4 Through this work we explore suited perovskite compositions towards faster reduction rates and improved syngas selectivity for thermochemical redox cycles, and also compare to traditionally infiltration processed materials of same chemistry. The high surface affinity between the metallic nanoparticles and the perovskite backbone, in which they are anchored, offers relevant advantages in terms of microstructural stability for high temperature thermochemical fuel production.
In the first part of the talk we will cover the materials design guidelines that result in exsolved-perovskite structures with increased particle coverage and size distribution, exploring the chemical nature of the nanoparticles and interfaces of the cermets. Secondly, their performance for syngas production tested under chemical looping reforming cycles will be evaluated and benchmarked with state-of-the-art materials, revealing the improved syngas production performance of exsolution-promoted perovskites and the high stability of such materials under prolonged cycling.5 These results show great promise for exsolution cermet processing route in improving fuel production kinetics, syngas yields and materials stability, opening new avenues for materials design and process optimization.
1 M. Kubicek, A. H. Bork and J. L. M. Rupp, J. Mater. Chem. A, 2017, 5, 11983–12000.
2 P. T. Krenzke, J. R. Fosheim and J. H. Davidson, Sol. Energy, 2017, 156, 48–72.
3 J. T. S. Irvine, D. Neagu, M. C. Verbraeken, C. Chatzichristodoulou, C. Graves and M. B. Mogensen, Nat. Energy, 2016, 1, 15014.
4 T. Zhu, H. E. Troiani, L. V. Mogni, M. Han and S. A. Barnett, Joule, 2018, 2, 478–496.
5 A.J. Carrillo, K. Kim, Z. Hood, A.H. Bork, J.L.M. Rupp, in review, 2018