Interplay between geometric and electronic structures of Pt entities over TiO2 for CO oxidation

Monodispersed Pt colloids with a mean size of 2 nm were deposited uniformly on the {110} facets of a rod-shaped rutile TiO2, forming a well-defined Pt/TiO2 system. Oxidative treatment of this precursor at elevated temperatures re-dispersed the Pt particles into clusters and single-atoms. Air-calcination at 673 K partially oxidized the Pt particle surface, while calcination at 773 K yielded PtOx clusters of 1.6 nm in 7–8 atomic layers. Further calcination at 873 K formed a mixture of raft-like PtOx clusters (1.6 nm, 1–2 atomic layers) and cationic single-atoms. When tested for CO oxidation at 373 K, the Pt particles showed a higher activity than the PtOx clusters, whereas the cationic single-atoms were much less active. Subsequent H2-reduction at 473 K converted the partially oxidized Pt particles into the metallic species, but they were encapsulated by TiO2−x overlayers because of the strong metal–support interactions, which decreased the activity dramatically. H2-reduction of the PtOx clusters at 473 K enhanced the fraction of metallic Pt species without changing the size and geometry, and promoted the activity substantially. H2-treatment of Pt single-atoms at 473 K increased the activity only moderately because most Pt species still kept at cationic species. These results straightforwardly differentiated the catalytic behavior of Pt particles, clusters and single-atoms at the same metal loading and over the same TiO2 support, and further demonstrated that the electronic structures of Pt entities played a decisive role in the catalytic oxidation, in addition to the specified sizes.