Effect of ceria on the MgO-γ-Al2O3 supported CeO2/CuCl2/KCl catalysts for ethane oxychlorination
A series of CeO2-doped CuCl2-KCl/MgO-γ-Al2O3 catalysts were prepared and characterized by BET, XRD, H2-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 (O2− 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 Cl2 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.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (120 K)Download as PowerPoint slideHighlights► Three type ceria exist on catalyst: dispersed, crystallized, large particles. ► Catalyst with crystallized ceria enhanced activity of ethane oxychlorination. ► Crystallized ceria contains larger amount of capping oxygen species (O2−/O−). ► Oxygen species accelerate oxidation of Cu+ to Cu2+ and form more weak acid sites.
Journal: Applied Catalysis A: General - Volume 400, Issues 1–2, 30 June 2011, Pages 104–110