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