Turnover Rate and Reaction Orders for the Complete Oxidation of Methane on a Palladium Foil in Excess Dioxygen

Abstract

The turnover rate and reaction orders for the combustion of methane in excess oxygen over Pd foils were in agreement with literature results reported for supported catalysts. The rate equation was r=k[CH₄]^0.7[O₂]^0.2[H₂O]^−0.9. The turnover rate on the Pd foil was 59×10⁻² s⁻¹ at 550 K, 160 Torr O₂, 16 Torr CH₄, 1 Torr H₂O, and N₂ balance to 800 Torr, with the number of active sites defined as the number of surface Pd atoms calculated from the initial geometric area of the foil. This rate is 3 times higher than the highest value reported in the literature for supported catalysts. The surface area of the foil, measured by isotopic exchange of surface oxygen with ¹⁸O₂, increased by a factor of approximately 2 after reaction. The main species observed on the surface after reaction by XPS was PdO. Sample activation during the reaction was not observed. The reaction was carried out in a batch reactor at 598 K and atmospheric pressure with characterization before and after reaction by X-ray and Auger spectroscopies and temperature-programmed desorption.