(704g) Influence of Support and Environment on the Structure and Properties of Oxide Supported Isolated Pt Atoms

Atomically dispersed Pt catalysts are potentially attractive for use in a range of chemical conversion process from automotive oxidation catalysis to hydrocarbon upgrading, as they maximize utilization of the precious metal. Developing structure function relationships between the local environment and oxidation state of single Pt atoms on oxide supports and their catalytic properties remains a challenge. These challenges exist due to (1) the inherent small size of these species, which makes their characterization difficult, (2) differences in their local environments on the support that potentially causes heterogeneity in their chemical and catalytic properties across a given sample, and (3) the low stability of atomically dispersed species at elevated temperatures under reactive environments and during characterization.

Here we demonstrate an approach to overcome these challenges and synthesize oxide supported isolated Pt species that do not sinter to form Pt clusters through pre-treatment, characterization, and reactivity analysis. We use a combination of site specific and sample averaged characterization to unambiguously identify isolated Pt atoms and understand their structure and reactivity. The effects of support composition (TiO₂ and CeO₂) and pretreatment conditions (oxidation and reduction pre-treatment at varying temperature) on the local coordination and catalytic properties of isolated sites will be discussed. Kinetic measurements and site-specific probe molecule characterization allow for mechanistic comparisons between isolated Pt atoms in various local coordination environments and ~1 nm Pt nanoparticles supported on reducible oxides in the context of CO oxidation catalysis.