Physico-chemical and catalytic study of the CO/SiO2 catalysts

This paper is focused on the physico-chemical and catalytic properties of Co/SiO2 catalysts. Silica-supported cobalt catalysts were prepared by sol-gel and impregnation methods and characterized by BET measurements, temperature programmed reduction (TPRH2), X-ray diffraction (XRD), and thermogravimetry-mass spectroscopy (TG-DTA-MS). The sol-gel method of preparation leads to metal/support catalyst precursor with a homogenous distribution of metal ions into bulk silica network or on its surface. After drying the catalysts were calcined at 500, 700, and 900degreesC. The reducibility of the supported metal oxide phases in hydrogen was determined by TPR measurements. The influence of high temperature-atmosphere treatment on the phase composition of CO/SiO2 catalysts was investigated by XRD and TG-DTA-MS methods. At least five crystallo-graphic cobalt phases may exist on silica: metallic Co, Coo, CO3O4, and two different forms of Co2SiO4 cobalt silicate. Those catalysts in which cobalt was chemically bonded with silica show worse reducibility as a result of strongly bonded Co-O-Si species formed during high-temperature oxidation. The TPR measurements show that a gradual increase in the oxidation temperature (500-900degreesC) leads to a decrease in low-temperature hydrogen reduction effects ( < 600degreesC). The decrease of cobalt oxide reduction degree is caused by cobalt silicate formation during the oxidation at high temperature (T less than or equal to 1000degreesC). The catalysts were tested by the reforming of methane by carbon dioxide and methanation of CO2 reactions.