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 Pt-0/TiO2 reduced by H-2 at elevated temperature. It is confirmed that titanium oxide of low-valence is transferred onto the surface of Pt-0 particulates to encapsulate the surface via a strong metal-support interaction under reducing atmosphere. It is also found for the first time that Pt-0 atom is diffused into the lattice of TiO2 to occupy the oxygen vacancy (V-O(center dot center dot)) and accept one electron from adjacent Ti3+ forming a localized Pt-Ti4+ bond. This differs from the strong metal-support interaction under oxidizing atmosphere. Namely, although the Pt-0 atom is also diffused into the lattice of TiO2 under oxidizing atmosphere, it replaces Ti atom and forms a Pt2+-O2- bond. Moreover, the strong metal-support interaction under oxidizing atmosphere results in increased photocatalytic activity of Pt-0/TiO2, while the strong metal-support interaction under reducing atmosphere leads to decreased photocatalytic activity of Pt-0/TiO2. (C) 2011 Elsevier B.V. All rights reserved.