Synergistic catalytic effect of (Ce,Cr)xO2 and HZSM-5 for elimination of chlorinated organic pollutants

Abstract

A series of y(Ce,Cr)xO2/HZSM-5 composite materials (with different mass ratios of (Ce,Cr)xO2 to the HZSM-5 zeolite) are firstly constructed via traditional deposition–precipitation method, and then evaluated for eliminating low concentration chlorinated organic pollutants with different molecule structures. Compared to single (Ce,Cr)xO2 or HZSM-5, the synergistic catalytic effect between (Ce,Cr)xO2 and HZSM-5 improves the destructive efficiency of y(Ce,Cr)xO2/HZSM-5. This is due to that the abundant strong/weak acid centers on HZSM-5 firstly favor the adsorption and dechlorination of the chlorinated organic molecules, while the superior oxidation property of (Ce,Cr)xO2 promotes the oxidative destruction of these Cl-VOCs (chlorinated volatile organic compounds) and the by-products, and also suppresses the surface deposition of chlorine and carbon species. Particularly, the (Ce,Cr)xO2/HZSM-5 catalyst with the same weight of (Ce,Cr)xO2 and HZSM-5 (50%:50% for (Ce,Cr)xO2:HZSM-5) exhibits the highest oxidative activity, since its appropriate concentration of acid and oxidative sites can play to the largest degree. Moreover, adding slight benzene or water into the reaction system slightly decreases the catalytic activity owing to the competitive adsorption effect on the active centers, whereas water reduces the formation of by-products, since it can accelerate the eliminating of the surface chlorine species. The preferable catalytic activity and durability in the continuous long-time reaction reveals that the (Ce,Cr)xO2/HZSM-5 catalyst deserves more attention and is potential for industrial application to eliminate the chlorinated organic pollutants.