Formation of Surface Platinum Oxides in the Interaction of the Pt/Sibunit Catalysts with NO 2 : Estimates of the Width of Oxide Shell from XPS Data

The method of X-ray photoelectron spectroscopy (XPS) using two types of radiation, nonmonochromatic Al K α ( h ν = 1486.6 eV) and monochromatic Ag L α ( h ν = 2984.3 eV), was used to study the interaction of the Pt/C (C = Sibunit) catalysts with NO 2 , which occurs in the preparation chamber of an XPS spectrometer at room temperature and NO 2 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 PtO 2 oxides. The ratio of intensities Pt4 f and Pt3 d 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 PtO 2 .