Co3O4/SiO2 catalysts for CO oxidation were prepared by conventional incipient wetness impregnation followed by calcination at various temperatures. Their structures were characterized with X-ray diffraction, laser Raman spectroscopy, X-ray photo-electron spectroscopy, temperature-programmed reduction and X-ray absorption fine structure spectroscopy. Both X-ray diffraction and Raman spectroscopy detected only the existence of Co3O4 crystallites in all catalysts. However, X-ray photo-electron spectroscopy results indicate that excess Co2+ ions were present on the surface of Co3O4 in Co3O4(200)/SiO2 as compared with bulk Co3O4. Meanwhile, temperature-programmed reduction results suggest the presence of surface oxygen vacancies on Co3O4 in Co3O4(200)/SiO2, and X-ray absorption fine structure spectroscopy results demonstrate that Co3O4 in Co3O4(200)/SiO2 contains excess Co2+. Increasing calcination temperature results in oxidation of excess Co2+ and the decrease of the concentration of surface oxygen vacancies, consequently the formation of stoichiometric Co3O4 on supported catalysts. Among all Co3O4/SiO2 catalysts, Co3O4(200)/SiO2 exhibits the best catalytic performance towards CO oxidation, demonstrating that excess Co2+ and surface oxygen vacancies can enhance the catalytic activity of Co3O4 towards CO oxidation. These results nicely demonstrate the effect of calcination temperature on the structure and catalytic performance towards CO oxidation of silica-supported Co3O4 catalysts and highlight the important role of surface oxygen vacancies on Co3O4.

Effect of Calcination Temperature on Surface Oxygen Vacancies and Catalytic Performance towards CO Oxidation of Co3O4 Nanoparticles Supported on SiO2. J.Li, Z.Jiang, K.Qian, W.Huang: Chinese Journal of Chemical Physics, 2012, 25[1], 103