(762b) Density-Dependent Deactivation Mechanism in Supported Catalysts By High-Temperature Decomposition of Particles into Single Atoms

Any precious metal catalyst needs to be thermally stable for extended periods of times to be viable for large-scale industrial implementation. Unfortunately, precious metal nanoparticles tend to deactivate due to loss of reactive surface area, caused by growth in nanoparticle size. This deactivation mechanism motivates the need for large quantities of precious metals in emissions control catalysts to ensure effective catalysis over the application lifetime. Current research and conventional wisdom focus on maximizing distances between nanoparticles in order to minimize their interactions and subsequent particle growth. Here, we demonstrate that this might not always be the best solution: by utilizing colloidally-synthesized catalysts that allow independent control of nanoparticle size and particle loading, we show that higher nanoparticle loadings are surprisingly more stable than sparse loadings. In this work, we identify a density-dependent atomic emission to inert Pd single-sites on an Al₂O₃ support – a phenomena suppressed at higher nanoparticle loadings. By combining DFT calculations with a statistic model, we find that above a certain particle loading threshold, stable interparticle atomic exchange may occur, with minimal atomic trapping at inert Al₂O₃ defect sites.