Total Oxidation of Methane over Pt/Cr2O3 Catalyst at Low Temperature: Effect of Pt0-Ptx+ Dipoles at the Metal-Support Interface

Catalytic activities of 1% Pt/Cr2O3 and 1% Pt/gamma-Al2O3 have been studied in total methane oxidation under lean conditions. The catalysts were characterized by DRS, XPS, and HRTEM. Low-conversion catalytic tests performed at 310 C revealed a TOF (h(-1)) value 28 times larger for 1% Pt/Cr2O3 in comparison with 1% Pt/gamma-Al2O3. The difference in TOF (h-1) and the differences in T-50 observed through the light-off curves (352 degrees C on 1% Pt/Cr2O3 and 460 degrees C on 1% Pt/gamma-Al2O3) are explained on the basis of strong differences in the methane oxidation rate dependences of the pre-exponential factor in the Arrhenius type equations. XPS analysis of 1% Pt/Cr2O3 revealed the presence of stable Pt Pt' catalytic sites of dipolar nature at the Pt/Cr2O3 interface. These sites are capable of increasing the probability of CH4 polarization, resulting in an increase of the strength and oriented collisions between the molecules and the catalyst surface, lowering the C-H bond energy, facilitating the abstraction of the first hydrogen in the adsorbed methane: the rate-determining step of methane oxidation. The high stability of the Pt Pt' sites has been associated with the electronic interactions between platinum and n-type semiconductor Cr2O3 at their interface.