Investigation of the behaviour of a Pd/γ-Al2O3 catalyst during methane combustion reaction using in situ DRIFT spectroscopy

In situ and/or operando DRIFT spectroscopy was applied to the study of the behaviour of a Pd (2 wt.%)/γ-Al2O3 catalyst, used in methane combustion, under various conditions. Under conventional O2-rich reaction conditions, spectator species (carbonates and/or formates) could be observed, but no surface intermediate species. No differences were observed under reaction conditions in function of the initial oxidation state of palladium. Formates/carbonates species were identified at low temperature (<400 °C) and disappeared when CO2 production started. They are not involved in the overall reaction pathway of methane oxidation and are thus suggested to be spectator species. Their production requires a continuous source of CO and would come from the interaction of CO with OH-groups of the γ-alumina support. Under O2-lean (O2/CH4 = 2) conditions, CO bridging on metallic palladium (Pdx0-CO) is observed at high temperature (>400 °C), evidencing incomplete oxidation of methane. Based on previous operando Raman studies, a mechanistic scheme is proposed, which takes into account the various surface phenomena observed.