The optimization of supported metal catalysts predominantly focuses on engineering the metal site, for which physical insights based on extensive theoretical and experimental contributions have enabled the rational design of active sites. Although it is well known that supports can influence the catalytic properties of metals, insights into how metal-support interactions can be exploited to optimize metal active-site properties are lacking. Here we utilize in situ spectroscopy and microscopy to identify and characterize a support effect in oxide-supported heterogeneous Rh catalysts. This effect is characterized by strongly bound adsorbates (HCO) on reducible oxide supports (TiO and NbO) that induce oxygen-vacancy formation in the support and cause HCO-functionalized encapsulation of Rh nanoparticles by the support. The encapsulation layer is permeable to reactants, stable under the reaction conditions and strongly influences the catalytic properties of Rh, which enables rational and dynamic tuning of CO-reduction selectivity.

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 TiO. In these structures, isolated Pt atoms, Pt, remain stable through various conditions, and spectroscopic evidence suggests Pt species exist in homogeneous local environments. Comparing Pt to ∼1 nm preoxidized (Pt) and prereduced (Pt) Pt clusters on TiO, we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Pt ≪ Pt < Pt. Pt species exhibited a 2-fold greater turnover frequency for CO oxidation than 1 nm Pt clusters but share an identical reaction mechanism. We propose the active catalytic sites are cationic interfacial Pt atoms bonded to TiO and that Pt exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO. This approach should be generally useful for studying the behavior of supported precious metal atoms.

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