In-situ XPS and XAS Studies of a New Phenomenon of Kinetic Hysteresis in Selective Methane Oxidation over Platinum
Recently, we discovered a new phenomenon of kinetic hysteresis in selective methane oxidation over platinum catalysts. To establish the causes of this phenomenon, we studied changes in the oxidation state of active component in real Pt/γ-Al2O3 catalysts by in-situ X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). In-situ XPS experiments revealed the presence of kinetic hysteresis even at low pressures (~ 0.01 mbar). Analysis of the in-situ XPS spectra showed that the catalyst activation was associated with partial reduction of the supported platinum. The XAS data also implied that the activation was accompanied by predominant formation of the metallic platinum, while oxidation of the platinum surface led to deactivation.