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/TiO2system.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 Pt Oxclusters of 1.6 nm in 7–8 atomic layers.Further calcination at 873 K formed a mixture of raft-like PtOxclusters(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 Pt Oxclusters,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–xoverlayers because of the strong metal–support interactions,which decreased the activity dramatically.H2-reduction of the PtOxclusters at473 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 TiO2support,and further demonstrated that the electronic structures of Pt entities played a decisive role in the catalytic oxidation,in addition to the specified sizes.