(617f) Dynamical Evolution of Atomically Dispersed Precious Metals on Oxide Supports

Precious metals are widely used in industrial and automobile catalysts to facilitate transformations that meet energy and material needs and emission standards. As these resources are becoming increasingly scarce, the catalysis community is focusing efforts on identifying more viable atom-efficient catalysts. One way to accomplish this is by making all atoms available for reaction by atomically dispersing the metal on a stable support such as an oxide. While microscopy and spectroscopy combined with computational studies yield critical insights into metal coordination, the study of operando characteristics remain challenging as an undercoordinated metal atom is likely to be mobile under reaction conditions. Computational catalysis studies that traditionally rely on a zero-kelvin or static quantum chemistry methods do not provide an adequate description of the dynamically evolving site. We are developing a dynamical picture of the active site and reaction mechanisms by combining static quantum chemistry (specifically density functional theory or DFT) with ab initio molecular dynamics (AIMD). Our group uses the automobile exhaust reaction of CO oxidation as model chemistry and atomically dispersed Pt-group metals on rutile TiO₂ as the representative catalyst. Our high-temperature AIMD studies uncover the formation of near-linear O-Pt-O configurations that are thermally stable but not identified previously with conventional DFT. The metal atom also exhibits varying degrees of stability in the presence of different adsorbates at reaction temperatures, with diffusion coefficients that are qualitatively consistent with adsorbate binding energy. We are combining these insights with DFT-driven mechanistic studies to identify preferred CO oxidation mechanisms based on both turnover frequencies as well as the dynamical stability of the metal atom in the presence of reaction intermediates. Based on this analysis and its extension to a multitude of metal coordination sites on the support, we aim to develop a protocol for determining site-averaged, site-optimized kinetics for these systems.