Catalytic behavior and synergistic effect of nanostructured mesoporous CuO-MnO_x-CeO_2 catalysts for chlorobenzene destruction

摘要

Mesoporous CuO-MnO_x-CeO_2 composite metal oxides with different copper and manganese loadings were prepared by a urea-assistant hydrothermal method, and were further adopted for the complete catalytic combustion of chlorobenzene. The effects of reaction conditions such as inlet reagent concentration and water feed concentration on chlorobenzene combustion were also studied. The structure and textural properties of the synthesized catalysts were characterized via the XRD, N_2 adsorption/desorption, FE-SEM, TEM, H_2-TPR, O_2-TPD, and XPS techniques. The characterization results reveal that the presence of a small amount of Mn species can facilitate the incorporation of Cu and Mn ions into ceria lattice to form Cu-Mn-Ce-O solid solution. The synergistic effect of Cu and Mn species can reduce the redox potential of the composite catalysts, and produce large amounts of oxygen vacancies in the interface of CuO_x, MnO_x, and CeO_2 oxides. The catalyst with Cu/Mn atomic ratio of 1/1 exhibits the best chlorobenzene elimination capability, oxidizing about 95% of the inlet chlorobenzene at 264 ℃ with CO_2 selectivity higher than 99.5%. The concentration and mobility of the chemically adsorbed oxygen are vital for the effective removal of surface Cl species, which inhibits the dissociation of oxygen molecules and decreases the reducibility of the copper and manganese species. It can be rationally concluded that the superior catalytic performance and durability of the mesoporous CuO-MnO_x-CeO_2 composite oxides are primarily attributed to the higher surface oxygen concentration and better active oxygen mobility.