Role of CeO2 Promoter in Co/SiO2 Catalyst for Fischer-Tropsch Synthesis

Fischer-Tropsch (FT) synthesis is gaining increased 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, and especially promote the formation of high hydrocarbons, but the role played by ceria is still controversial. In this study, CeO2-promoted Co/SiO2 catalysts were prepared using the incipient wetness impregnation method and were characterized using X-ray diffraction, temperature-programmed reaction, X-ray photoelectron spectroscopy, scanning electron microscopy, H-D isotopic exchange, and D2 pulse experiment. The results showed that the addition of 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 is bonded to the Co atom with its carbon atom and to the adjacent partially reduced cerium oxide with its oxygen atom. The D2 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 high-value diesel oil and lubricating oil.