Role of CeO2 promoter in CO/SiO2 catalyst for Fischer-Tropsch synthesis

Fischer-Tropsch (FT) synthesis is gaining more and more interest because of the need of high purity diesel fuels and lubricating oil. The cobalt-based catalyst is well known for its activity in the FT reaction. The addition of a small amount of ceria to the Co/SiO2 catalyst can increase the turnover rate and C5+ selectivity, especially promote the formation of high hydrocarbons, but the role of ceria is still of controversy. In this study, the CeO2-promoted Co/SiO2 catalyst was prepared by the incipient wetness impregnation method and characterized by X-ray diffraction, temperature-programmed reaction, X-ray photoelectron spectroscopy, scanning electron microscopy, H-D isotopic exchange, and D-2 pulse experiment. The results showed that adding a small amount of ceria improved the dispersion of cobalt, decreased the electron density of the cobalt particle, and enhanced the dissociation of CO on the catalyst surface. This might be due to the new catalytic active sites at which CO bonded to the Co atom with its carbon atom and to the adjacent partially reduced cerium oxide with its oxygen atom. The D-2 pulse in the FT reaction showed that the addition of ceria to CO/SiO2 increased the concentration of surface active carbon species (-CH2-), the chain growth probability, and the selectivity for long chain hydrocarbons, which favored the formation of the high value diesel oil and lubricating oil.