A highly active Pd/H-ZSM-5 catalyst in lean methane combustion prepared through sol-gel method and treated by reduction-oxidation
Catalytic combustion is now considered as an effective measure in the mitigation of anthropogenic methane emission contributing to the greenhouse effect, which demands proper catalysts of high activity at low temperature and high stability at elevated temperature. Herein, a series of Pd/H-ZSM-5 catalysts were prepared via sol-gel method and treated by reduction and oxidation; the effect of Pd particle size and redox treatment on the catalytic activity of Pd/H-ZSM-5 in lean methane combustion was investigated. The results indicate that the catalytic activity of Pd/H-ZSM-5 varies according to a volcano-shape trend with an increase in the Pd particle size from 3.5 to 10.1 nm; the Pd/H-ZSM-5 catalyst with a Pd particle size of around 5.2 nm exhibits the highest activity in lean methane oxidation. Moreover, the catalytic activity of Pd/H-ZSM-5 can be greatly enhanced through the reduction-oxidation treatment, which may reconstruct the palladium particles on the H-ZSM-5 surface and strengthen the interaction between the Pd species and the acid sites on the H-ZSM-5 support. The Pd/H-ZSM-5 catalyst after the reduction and oxidation treatment (with a Pd particle size of 5.2 nm) exhibits excellent activity in lean methane combustion, giving a complete methane oxidation to carbon oxide at as low as 300 °C. This work should be of great benefit to clarifying the relationship between the structure and performance for the acid zeolite supported Pd catalysts as well as designing efficient catalyst in the lean methane combustion at low temperature.