Formation of Surface Platinum Oxides in the Interaction of the Pt/Sibunit Catalysts with NO2: Estimates of the Width of Oxide Shell from XPS Data

Abstract

The method of X-ray photoelectron spectroscopy (XPS) using two types of radiation, nonmonochromatic AlK_α (hν = 1486.6 eV) and monochromatic AgL_α (hν = 2984.3 eV), was used to study the interaction of the Pt/C (C = Sibunit) catalysts with NO₂, which occurs in the preparation chamber of an XPS spectrometer at room temperature and NO₂ pressure, equal to 3 × 10^–6 mbar. It was found that, under these conditions, platinum was partially oxidized and metallic core becomes covered with a shell formed by a mixture of PtO and PtO₂ oxides. The ratio of intensities Pt4f and Pt3d_5/2 belonging to platinum oxides to the corresponding intensities of metallic platinum was used to estimate the width of oxide shell. For two of the three studied Pt/C samples, the width of the shell was 0.15–0.3 nm, which approximately corresponds to one monolayer of platinum oxide with a stoichiometry of PtO or PtO₂.