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

5 years ago

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

Igor O. Klembovskii, Evgeny I. Vovk, Alexander V. Kalinkin, Mikhail Yu. Smirnov, Valerii I. Bukhtiyarov

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-O_sub], and then, into the PtO and PtO₂ oxides. If only the first state of platinum [Pt-O_sub] is formed, it demonstrates exclusively high reactivity toward hydrogen. For the samples containing simultaneously [Pt-O_sub], 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-O_sub] 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.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04569

DOI: 10.1021/acs.jpcc.7b04569