Effect of Surface Oxygen on the Activation of Methane on Palladium and Platinum Surfaces

Active surfaces for the catalytic oxidation of CH4 on Pd and Pt were identified using infrared reflection absorption spectroscopy (IRAS) with a wide spectrum range (4000-450 cm(-1)) that is capable of measuring both the surface species and changes specific to the surface. Both the metallic Pd and Pt surfaces were found to be significantly less active for the oxidation of CH4 than the PdO surface under near-stoichiometric conditions. However, the metallic surfaces become very active under oxygen-poor conditions. This work represents the first evidence of such high activity for CH4 oxidation on metallic Pt-group metal surfaces. A comparison of the catalytic behaviors of CH, and CO oxidation demonstrates that the chemisorbed oxygen with near-saturated coverage suppresses the activation of CH4; additionally, the involvement of an unoccupied surface site, surface cation, or metallic atom can significantly enhance the activity for the activation of CH4. The current results also demonstrate that oxygen is depleted sharply when switching from the combustion to the reforming region in the partial oxidation of methane to syngas.