Unraveling The Catalytic Effect of Hydrogen Adsorption on Pt Nanoparticle Shape-Change

The activity of metal catalysts depends sensitively on dynamic structural changes that occur during operating conditions. The mechanistic understanding underlying such transformations in small Pt nanoparticles (NPs) of ~1-5 nm in diameter, commonly used in hydrogenation reactions, is currently far from complete. In this study, we investigate the structural evolution of Pt NPs in the presence of hydrogen using long time-scale reactive molecular dynamics (MD) simulations paired with experimental X-ray absorption spectroscopy. From these comparisons, we obtain atomic-level mechanistic insights into `order-disorder' structural transformations exhibited by highly dispersed Pt NP catalysts upon exposure to hydrogen. We report the emergence of previously unknown candidate structures in the 1 nm Pt NP size range, where exposure to hydrogen leads to the appearance of a `quasi-icosahedral' intermediate symmetry, followed by the formation of `rosettes' on the NP surface. Hydrogen adsorption is found to catalyze these shape transitions by lowering their temperatures and increasing the apparent rates at which these candidate structures appear, revealing the mutually catalytic and dynamic nature of interaction between nanoparticle and adsorbate. This study offers a new pathway for deciphering the reversible evolution of catalyst structure resulting from the chemisorption of reactive species, enabling the determination of active sites and improved interpretation of experimental results with atomic resolution.