ALD-Fabricated MgO-Overcoats to Control Sintering of Model Pt Nanoparticle Catalysts—The Power of Synchrotron X-Ray Scattering Tools

Nanoparticle sintering is a prime mechanism of catalyst deactivation.[1] During sintering, nanoparticle growth decreases the amount of active surface area for catalytic reaction, leading to performance losses. Amongst the explored design strategies to prevent nanoparticle sintering, partial overcoating of the catalyst surface presents a viable route. Recently, we demonstrated the application of atomic layer deposition (ALD) to deposit sub-monolayer MgO overcoats on model SiO₂-supported Pt nanoparticle catalysts to physically prevent sintering, while keeping controlled fractions of the Pt surface available for reaction.[2] The deposited MgO layer can range from sub-monolayers to nm-range and has been proven to exhibit an increase in the onset temperature of sintering.<br/><br/>Herein, we explore synchrotron-based X-ray scattering and diffraction tools to monitor the structural evolution of ALD-fabricated, MgO-overcoated Pt nanoparticles <i>in situ</i> during gas treatments which stimulate sintering. In particular, the MgO-overcoated Pt nanoparticles are subjected to propane dehydrogenation reaction and O₂ regeneration cycles at 600⁰C and compared to their overcoat-free Pt analogues. The real-time Pt nanocrystal size and orientation are respectively probed by complementary <i>in situ</i> grazing-incidence small-angle X-ray scattering (GISAXS)[2, 3] and wide-angle X-ray scattering (GIWAXS)[4] (ALBA synchrotron). <i>In situ</i> GISAXS evidences that the MgO-overcoat leads to a decreased rate of nanoparticle sintering. Surprisingly, complementary GIWAXS data shows that the crystallographic evolution of nanoparticles, and in particular their orientation on the SiO₂ support, is strongly influenced by the MgO-overcoat. We therefore anticipate that ALD-tailored partial overcoats not only form a technology to control the sintering rate of nanoparticles, but can also be instrumentalized to direct crystal orientation under harsh post-synthesis processing conditions.<br/><br/>References:<br/>[1] Dai, Y. Q.; Lu, P.; Cao, Z. M.; Campbell, C. T.; Xia, Y. N. The Physical Chemistry and Materials Science Behind Sinter-Resistant Catalysts. <i>Chem Soc Rev </i><b>2018</b>, <i>47</i> (12), 4314-4331. DOI: 10.1039/c7cs00650k.<br/>[2] Zhang, Z. W.; Filez, M.; Solano, E.; Poonkottil, N.; Li, J.; Minjauw, M. M.; Poelman, H.; Rosenthal, M.; Brüner, P.; Galvita, V. V.; et al. Controlling Pt Nanoparticle Sintering by Sub-Monolayer MgO ALD Thin Films. <i>Nanoscale </i><b>2024</b>, <i>16</i> (10), 5362-5373. DOI: 10.1039/d3nr05884k.<br/>[3] Dendooven, J.; Ramachandran, R. K.; Solano, E.; Kurttepeli, M.; Geerts, L.; Heremans, G.; Rongé, J.; Minjauw, M. M.; Dobbelaere, T.; Devloo-Casier, K.; et al. Independent Tuning of Size and Coverage of Supported Pt Nanoparticles using Atomic Layer Deposition. <i>Nat Commun </i><b>2017</b>, <i>8</i>. DOI: 10.1038/s41467-017-01140-z.<br/>[4] Solano, E.; Dendooven, J.; Deduytsche, D.; Poonkottil, N.; Feng, J. Y.; Roeffaers, M. B. J.; Detavernier, C.; Filez, M. Metal Nanocatalyst Sintering Interrogated at Complementary Length Scales. <i>Small </i><b>2023</b>, <i>19</i> (5). DOI: 10.1002/smll.202205217.