Effect of vacuum impregnation on the performance of Co/SiO2 Fischer-Tropsch catalyst

Two silica-supported cobalt catalysts were prepared by incipient wetness impregnation under atmospheric and vacuum conditions.N2 physisorption,H2 chemisorption,XRD,SEM,TEM,XPS and H2-TPR were used to characterize the catalysts.The results showed that the impregnation methods had an effect on the size,dispersion and reducibility of cobalt particles.Under vacuum conditions,cobalt-containing steeping liquor could penetrate into the inner pores of silica support and more bivalent cobalt oxides were formed in the Co3O4 crystallites.Furthermore,cobalt precursors were rarely inclined to agglomerate and the smaller cobalt particles were uniform on the support,which led to the higher activity of the Co/SiO2 (B) catalyst than the normal one under the reaction conditions of 483-523 K,1-2 MPa,gas hourly space velocity of 500-1000 h-1 and molar ratio of H2/CO =0.5-2.0.