Synergistic Effect between Pd and Nonstoichiometric Cerium Oxide for Oxygen Activation in Methane Oxidation

Abstract

The catalytic behavior of activated oxygen on Pd/CeO2-x/Al2O3 catalyst as well as the synergistic effect between Pd and nonstoichiometric cerium oxide has been revealed through methane oxidation by comparison with Pd catalysts such as Pd/CeO2/Al2O3, Pd/CeO2/SiO2, Pd/Al2O3, and Pd/SiO2 catalysts. The highest activity for methane oxidation was observed on the Pd/CeO2-x/Al2O3 catalyst. This was ascribed to the deactivation of Pd, which was inhibited by the oxygen spillover from Pd to CeO2-x, where the enhanced oxygen storage capacity (OSC) was observed by the nonstoichiometric structure and the oxygen species were reversibly stored/released in the presence of methane. Kinetics studies of methane oxidation resulted in it being first order with respect to methane and a half order with respect to oxygen for Pd/CeO2-x/Al2O3 but nearly zero order with respect to oxygen for other catalysts. From temperature-programmed desorption (TPD), reduction (TPR), oxidation (TPO), and 18O tracer technique analyses, it was fou...