Effect of ceria on the MgO-γ-Al2O3 supported CeO2/CuCl2/KCl catalysts for ethane oxychlorination

A series of CeO2-doped CuCl2-KCl/MgO-gamma-Al2O3 catalysts were prepared and characterized by BET, XRD, H-2-TPR, FTIR-pyridine adsorption, NH3-TPD and XPS techniques. XRD, BET and TPR results show that three types of ceria species exist on the surface of catalysts: dispersed ceria, small aggregated crystalline CeO2 species and large ceria particles. It was found that copper-based catalysts modified with small aggregated crystalline ceria species exhibited higher conversion of ethane and selectivity to vinyl chloride compared to copper-based catalysts with dispersed ceria or large ceria particles. The promotional effects may be originated from the formation of large amount of surface capping oxygen species (O-2(-) or O-) due to structural defects and electronic properties of nonstoichimetric ceria. Moreover, these surface capping oxygen species accelerate oxidation of part of Cu+ to Cu2+, which are responsible for the increase of intermediate Cl-2 species in the process of ethane oxychlorination. NH3-TPD results show that the catalysts modified with small aggregated crystalline ceria species have a large amount of weak acidic sites on the surface, and these weak acidic sites benefit dehydrochlorination of dichloroethane. The activity tests revealed that the copper-based catalyst with cerium content x = 5 wt.% exhibited the highest activity due to the excellent coordination effect between ceria and copper species and the largest amount of weak acid sites for breaking C-H bonds and dehydrochlorination of dichloroethane. (C) 2011 Elsevier B.V. All rights reserved.