Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO2

Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO₂. In these structures, isolated Pt atoms, Pt_iso, remain stable through various conditions, and spectroscopic evidence suggests Pt_iso species exist in homogeneous local environments. Comparing Pt_iso to ∼1 nm preoxidized (Pt_ox) and prereduced (Pt_metal) Pt clusters on TiO₂, we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Pt_iso ≪ Pt_metal < Pt_ox. Pt_iso species exhibited a 2-fold greater turnover frequency for CO oxidation than 1 nm Pt_metal clusters but share an identical reaction mechanism. We propose the active catalytic sites are cationic interfacial Pt atoms bonded to TiO₂ and that Pt_iso exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO₂. This approach should be generally useful for studying the behavior of supported precious metal atoms.