Catalytic performance of Pd catalyst supported on CeO2 or ZrO2 modified beta zeolite for methane oxidation

Two kinds of oxide-zeolite composite support, Ce-beta and Zr-beta were prepared by a simple wet impregnation method and adopted for the preparation of palladium-based catalysts for catalytic oxidation of methane. The Pd/6.8Zr-beta catalyst showed superior methane oxidation performance, achieving T50 and T90 of 417°C and 451°C, respectively, together with robust hydrothermal stability. Kinetic analysis has shown that incorporating Zr into the catalyst significantly enhanced its efficiency, nearly tripling the turnover frequency (TOF) for methane combustion compared to the Pd/beta catalyst. This enhanced performance was attributed to the dispersion of Zr on the zeolite surface, which not only promoted the formation of active PdO sites but also helped maintain the high Pd2+ content via facilitating the oxygen migration during the reaction, thus improving both the catalyst's activity and stability. In the Pd/8.6Ce-beta catalyst, doped CeO2 tended to aggregate in the zeolite's pores, adversely affecting the catalyst's efficiency. This aggregation promoted the formation of inactive Pd4+ species, a result of the enhanced metal-support interaction. This finding is critical for understanding the implications of dopant selection in the design of high-activity methane oxidation catalysts.