Combined near-ambient pressure photoelectron spectroscopy and temporal analysis of products study of CH4 oxidation on Pd/γ-Al2O3 catalysts

Abstract

Vehicles that run on natural gas must be equipped with an exhaust gas after-treatment system to burn their unavoidable CH4 slip, which must not be released into the environment as CH4 is a potent greenhouse gas. Pd is known as a highly active catalyst material for CH4 oxidation. For this study, Pd was deposited on a γ-Al2O3 support and the as-received samples were pre-reduced and pre-oxidized, respectively. Near-Ambient Pressure Photoelectron Spectroscopy and the Temporal Analysis of Products methodology were combined to understand that both electronic states, namely PdO and Pd°, are active for the CH4 oxidation reaction, whereby the superior activity of the pre-reduced Pd/γ-Al2O3 catalyst was ascribed to the spill-over of OH-groups from the support to Pd. It was found that the reaction products, CO, CO2 and H2, were strongly and, to a large extent, adsorbed on the catalyst surface and were involved in reversible chemical interactions on the catalyst surface during the CH4 oxidation reaction on the Pd/γ-Al2O3 catalyst.