EFFECTS OF ETHANOL IMPREGNATION ON THE CATALYTIC PROPERTIES OF SILICA-SUPPORTED COBALT CATALYSTS

Silca-supported Co3O4 (6 wt% as Co) catalysts were prepared by pore vo lume impregnation of ethanol or aqueous cobalt nitrate solutions, and calcined in vacuo to 300 degrees C. The catalytic performances of thes e catalysts for oxidation and hydrogenation of CO were examined. All C o3O4/SiO2 catalysts were found to be very active in catalyzing oxidati on of CO to CO2 as compared to a commercial 1 wt% Pt/Al2O3. The ethano l-prepared catalysts exhibited higher activity than those of the aqua- prepared catalysts. Pre-calcination of the ethanol-prepared catalysts in oxygen at 600 degrees C resulted in a dramatic decrease in the acti vity. Temperature programmed oxidation indicated the presence of carbo n deposits on the surface of used catalysts. Infrared spectra showed t he continuous generation of CO2 when these catalysts were exposed to C O. These indicate the primary role of CO disproportionation in catalyt ic oxidation of CO on Co3O4 at low temperature and explain the sharp d ecrease in activity in the initial period. After reduction at 400 degr ees C, the ethanol-prepared catalysts were also found to be more activ e in catalyzing hydrogenation of CO, and produced less methane and ole fin (C2-C4) fraction. Higher turnover frequencies were observed after high temperature reduction (600 degrees C) as well, at which ethoxyl g roups were removed from silica surface. In both reactions, the enhance d activity for the ethanol-prepared catalysts can not be fully account ed for by the increase in the dispersion of Co3O4 or CO metal. This su ggests that the surface structures of Co3O4 or CO were further modifie d by the carbonaceous species derived from ethanol.