Cerium promoted Pd/HZSM-5 catalyst for methane combustion

A series of Pd/HZSM-5 (Si/Al2 = 165) catalysts without and with additives of oxides of La, Ce, Sm, Nd and Tb were prepared by the impregnation method, and characterized by XRD, Raman spectra, N2-adsorption, CO-chemisorption, O2-TPD and CH4-TPR techniques. The catalysts were investigated for low-temperature CH4 combustion, and CeO2 was found to have a significant promoting effect on the activity of Pd/HZSM-5. Pd–Ce/HZSM-5 showed the best methane combustion activity and the improved thermal/hydrothermal reaction stability among tested catalysts. The characterization results of catalysts indicated that CeO2 can effectively promote the formation of crystalline PdO and weaken the bond strength of Pd–O on Pd–Ce/HZSM-5, resulting in that Pd–Ce/HZSM-5 possessed lower temperatures for oxygen desorption and CH4 reduction than Pd/HZSM-5. This could be ascribed to the covalent property and large oxygen storage/supplying capacity of CeO2. It is believed that more active PdO species on Pd/HZSM-5 for low-temperature methane combustion process could be effectively promoted due to the introduction of CeO2.