Catalytic Combustion of Dichloromethane over HZSM-5-Supported Typical Transition Metal (Cr, Fe, and Cu) Oxide Catalysts: A Stability Study

In this paper, three kinds of HZSM-5-supported transition metal (Cr, Fe, and Cu) oxide catalysts were prepared by the wet impregnation method, and their stability performances for catalytic combustion of dichloromethane (DCM) were investigated. Different behaviors were observed for these three catalysts during a 300 min catalytic reaction running at 320 degrees C. It was found that the Cr-O/HZSM-5 catalyst showed good catalytic stability, while both Fe-O/HZSM-5 and Cu-O/HZSM-5 suffered obvious deactivation. Characterizations using XRD, BET, XPS, O-2-TG, O-2-TP-MS, NH3-IR, and temperature-programmed surface reaction (TPSR) techniques were then carried out to disclose the deactivation mechanisms. The results revealed that the main cause of the deactivation over the Fe-O/HZSM-5 catalyst was coke formation, which could be mainly attributed to its lower deep oxidation capacity of the intermediate products, i.e., the methoxy groups, and it could also be obtained that the Cu-O/HZSM-5 catalyst was severely poisoned by chlorine species owing to the formation of stable Cu(OH)Cl species. Based on the results above, it could be concluded that the close proximity and synergy between acidic sites and active oxygen species were crucial to avoid coke deposition during the chlorinated volatile organic compound catalytic oxidation process.