Cobalt Supported on Carbonized MgAl.sub.2O.sub.4 Spinel as Efficient Catalyst for CO Hydrogenation

Hydrogenation of carbon monoxide (Fischer-Tropsch synthesis) is a promising route to ultraclean motor fuels, base oils and petrochemicals on the basis of non-petroleum feed such as natural gas, coal and biomass. Although cobalt-based industrial catalysts for this process are in operation for many years, they still need to be improved in terms of specific activity and selectivity to target hydrocarbons. This paper describes the effect of catalyst support coating with carbon on the formation of cobalt active phase and catalytic performance in CO hydrogenation. Carbonization of Mg-Al spinel was performed by impregnating with aqueous glucose solution followed by thermal treatment in inert atmosphere. Thus prepared carbonized material was used for cobalt deposition by incipient wetness impregnation method. The catalysts were characterized by N.sub.2 adsorption-desorption, scanning electron microscopy, thermoanalytical measurements combined with mass spectrometry of released gases, X-ray diffraction and in situ magnetic measurements during activation in H.sub.2 flow. Catalytic performance in Fischer-Tropsch synthesis was assessed at T = 210 °C, P = 20 bar. The size of Co.sub.3O.sub.4 crystallites in calcined catalysts and metallic cobalt in activated catalysts decreases with carbon content in the support. Cobalt precursor is reduced completely to metal within 2 h in typical activation conditions for FTS cobalt catalysts: H.sub.2 flow, 450 °C. Activity in CO hydrogenation decreases while selectivity to higher hydrocarbons increases with carbon content. High proportion of olefins in synthesized light hydrocarbons (> 65%) is a remarkable feature of the elaborated catalysts.