XPS Study of Stability and Reactivity of Oxidized Pt Nanoparticles Supported on TiO2

The method of X-ray photoelectron spectroscopy was used to study the interaction of the model Pt/TiO2 catalysts with NO2 and the following reduction of the oxidized Pt nanoparticles in vacuum, hydrogen, and methane. It was shown that, while interacting with NO2 at room temperature, the metal Pt nanoparticles transform, first, into the phase which was tentatively assigned as particles containing subsurface/dissolved oxygen Pt-Osub, and then, into the PtO and PtO2 oxides. If only the first state of platinum Pt-Osub is formed, it demonstrates exclusively high reactivity toward hydrogen. For the samples containing simultaneously Pt-Osub, PtO, and PtO2, the highest reaction ability was demonstrated by PtO2; contrary to the other two oxidized states, it is reducing while kept in vacuum under X-ray irradiation. All three coexisting states of the oxidized platinum can be reduced when heated in vacuum as well as while interacting with hydrogen at room temperature. First, PtO2 is reduced to PtO. PtO and Pt-Osub begin being reduced after the complete consumption of PtO2. We propose that, when a sample contains simultaneously all three states of oxidized platinum, the supported particles have a core–shell structure with a nucleus of perturbed platinum containing oxygen atoms, which are covered with a film of Pt oxides. It was shown that none of the oxidized states of platinum react with methane at room temperature.