Abstract
The source of activity of metal/metal oxides has always been an interesting, important but highly challenging research topic in heterogeneous catalysis. In CO oxidation reaction, this work clarifies dispersion and support dictated activities of Pt including single-atom (Pt1), 2.8 nm (PtNP-S) and 36 nm (PtNP-L) Pt supported on both reducible TiO2 and “inert” Al2O3 supports. The X-ray absorption fine structure (XAFS) shows that chemical state of Pt is affected by both dispersion and support: Pt1 presents fully oxidized state in both Pt1/TiO2 and Pt1/Al2O3; PtNP-S in PtNP-S/TiO2 appear nearly oxidized state while about half of Pt is metallic state in PtNP-S/Al2O3; PtNP-L in both PtNP-L/TiO2 and PtNP-L/Al2O3 exhibit metallic state. All the Pt species supported on TiO2 present much lower apparent activation barriers (Eapp) than that on Al2O3. Moreover, Pt1/TiO2 possesses dozen times of efficiency than PtNP-S/TiO2 although they have similar Eapp values. A truth is finally made clear that a reducible metal oxide with low oxygen vacancy formation energy is critical to endow Pt/metal oxide a high activity and the single-atom dispersion of Pt is the way to maximize the active sites of Pt/metal oxide.
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