Study of high-temperature hydrogen reduced Pt0/TiO2 by X-ray photoelectron spectroscopy combined with argon ion sputtering—Diffusion-encapsulation effect in relation to strong metal–support interaction

X-ray photoelectron spectroscopy combined with Ar+ ion sputtering has been used to analyze the variation in the valence and concentration of Pt, Ti, and O of Pt0/TiO2 reduced by H2 at elevated temperature. It is confirmed that titanium oxide of low-valence is transferred onto the surface of Pt0 particulates to encapsulate the surface via a strong metal–support interaction under reducing atmosphere. It is also found for the first time that Pt0 atom is diffused into the lattice of TiO2 to occupy the oxygen vacancy (VOradical dotradical dot) and accept one electron from adjacent Ti3+ forming a localized Pt−single bondTi4+ bond. This differs from the strong metal–support interaction under oxidizing atmosphere. Namely, although the Pt0 atom is also diffused into the lattice of TiO2 under oxidizing atmosphere, it replaces Ti atom and forms a Pt2+single bondO2− bond. Moreover, the strong metal–support interaction under oxidizing atmosphere results in increased photocatalytic activity of Pt0/TiO2, while the strong metal–support interaction under reducing atmosphere leads to decreased photocatalytic activity of Pt0/TiO2.