Effects of Ethanol Impregnation on the Properties of Thoria-Promoted Co/SiO2Catalyst

Abstract

Two Th-added Co/SiO2catalysts were prepared by pore volume impregnation of 6 wt% Co3O4/SiO2with either aqueous or ethanol solutions. Smaller ThO2crystallites were obtained for the ethanol-prepared Th/Co3O4/SiO2. The reduction behavior of cobalt oxide was modified by aqueous impregnation. Furthermore, Th addition was found to be promotional in the case of ethanol impregnation, or detrimental in the case of aqueous impregnation, for the CO oxidation activity of Co3O4/SiO2. Th addition has no effect on the extent of reduction of cobalt phase, but (1) reduces the crystallite size of cobalt by hindering the sintering of cobalt metal; (2) increases the amount of hydrogen desorbed (150 or 190%), CO adsorbed (3 or 4 times), CO2evolved (2.6 or 4 times), and carbon deposited; (3) enhances the activity for CO disproportionation; (4) induces new CO adsorption modes, subcarbonyl-like species (Co(CO)x,x> 1) and multifold CO ((Co)xCO,x≥ 2); (5) decreases methanation activity; and (6) enhances the activity and the selectivity for higher hydrocarbons and olefins for Fischer–Tropsch synthesis. A roughening of the cobalt surface, which consists of steps and kinks induced by the decorated ThO2moieties around the interface area, is the proposed origin for the new adsorption and CO disproportionation sites. The more significant effects of Th addition when ethanol was employed as impregnation solvent instead of water is attributed to a more extensive Co–ThO2interface formed due to a better dispersed Th phase.