Effects of Ethanol Impregnation on the Catalytic Properties of Silica‐Supported Cobalt Catalysts

Abstract

AbstractSilca‐supported Co3O4 (6 wt% as Co) catalysts were prepared by pore volume impregnation of ethanol or aqueous cobalt nitrate solutions, and calcined in vacuo to 300 °C. The catalytic performances of these catalysts for oxidation and hydrogenation of CO were examined. All Co3O4/SiO2 catalysts were found to be very active in catalyzing oxidation of CO to CO2 as compared to a commercial 1 wt% Pt/Al2O3. The ethanol‐prepared catalysts exhibited higher activity than those of the aqua‐prepared catalysts. Pre‐calcination of the ethanol‐prepared catalysts in oxygen at 600 °C resulted in a dramatic decrease in the activity. Temperature programmed oxidation indicated the presence of carbon deposits on the surface of used catalysts. Infrared spectra showed the continuous generation of CO2 when these catalysts were exposed to CO. These indicate the primary role of CO disproportionation in catalytic oxidation of CO on Co3O4 at low temperature and explain the sharp decrease in activity in the initial period. After reduction at 400 °C, the ethanol‐prepared catalysts were also found to be more active in catalyzing hydrogenation of CO, and produced less methane and olefin (C2‐C4) fraction. Higher turnover frequencies were observed after high temperature reduction (600 °C) as well, at which ethoxyl groups were removed from silica surface. In both reactions, the enhanced activity for the ethanol‐prepared catalysts can not be fully accounted for by the increase in the dispersion of Co3O4 or CO metal. This suggests that the surface structures of Co3O4 or CO were further modified by the carbonaceous species derived from ethanol.