Performance of Pt/Cr2O3, Pt/ZrO2, and, Pt/γ-Al2O3 Catalysts in Total Oxidation of Methane: Effect of Metal-Support Interaction

We present the catalytic performance of Pt-supported Cr2O3, and ZrO2 (semiconductors), and gamma-Al2O3 (insulator) in CH4 oxidation under lean conditions. XPS analysis of the catalysts showed only Pt2+ at the Pt/gamma-Al2O3 surface, and stable (Ptx-Pty) dipolar catalytic sites at the surface of Pt/Cr2O3 and Pt/ZrO2. The presence of such dipolar moieties increases the polarization probability of methane molecules, resulting in an increment of the molecule's kinetic energy and in an increase of the strength of its impact with the catalyst surface, weakening the C-H bond energy and enhancing hydrogen detachment from CH4 adsorbed molecules. The detachment of this hydrogen is the ratedetermining step of the reaction. The formation and stability of the Pt-x-Pt-y dipolar moieties have been related to the electronic effects associated with platinum and metal oxide semiconductor support interactions. Results reported in this investigation demonstrate the possibility of tuning the catalytic activity of Pt supported on metal oxides for methane oxidation by controlling the nature of the Pt-x-Pt-y dipolar moieties at the surface of metal oxide supports by selecting the semiconducting supports of suitable work functions.