Methane oxidation over Pt/Al2O3 and Pd/Al2O3 catalysts under transient conditions

We communicate experimental results for the oxidation of methane by oxygen over alumina supported Pd and Pt monolith catalysts under transient conditions. Temperature programmed reaction (TPReaction) and reactant pulse-response (PR) experiments have been performed, using a continuous gas-flow reactor equipped with a downstream mass spectrometer for gas phase analysis. Special attention was paid to the influence of gas composition changes, i.e., O2 and H2 pulsing, respectively, on the methane conversion. For Pt/Al2O3 oxygen pulsing can significantly increase the methane conversion which can be even further improved by pulsing hydrogen instead. Such transient effects are not observed for the Pd/Al2O3 catalyst for which instead constantly lean conditions is beneficial. Our results suggest that under lean conditions Pd and Pt crystallites may undergo bulk- and partial (surface oxide formation) oxidation, respectively, which for Pd results in more active surfaces, while for Pt the activity is reduced. The latter seems to connect to a lowering of the ability to dissociate methane.