INVESTIGATION OF COAL2O4, CU/COAL2O4 AND CO/COAL2O4 CATALYSTS FOR THE FORMATION OF OXYGENATES FROM A CARBON MONOXIDE-CARBON DIOXIDE-HYDROGEN MIXTURE

A cobalt alumina spinel has been prepared by coprecipitation and a series of catalysts have been made from the spinel by impregnation with varying amounts of copper and cobalt salts. The crystalline phases present have been identified by X-ray diffraction, and the reducibility of the catalysts has been determined by temperature-programmed reduction. The activities and selectivities of the various catalysts have been measured in the CO/CO2/H2 reaction at 40 bar pressure and a temperature of 270-degrees-C. The results show that after reduction, the CoAl2O4 catalyst is capable of producing both methane and methanol, indicating that copper free cobalt catalysts have the capacity to produce oxygenates. The addition of copper was found to increase the degree of reduction of the cobalt, leading to a large increase in the activity for the formation of hydrocarbons. However, as the copper content was increased the activity goes through a maximum, which is attributed to a progressive poisoning of the metallic cobalt by copper. Since it is observed that the activity for the formation of methanol and other oxygenates also passes through a maximum, it is concluded that the formation of methanol and other oxygenates is not directly related to the amount of the Cu/Co bimetallic phase present in the various catalysts. The results also show the formation of a significant amount of acids in addition to alcohols and it is suggested that in Cu/Co/ZnO/Al2O3 catalysts the preferential formation of alcohols may be due to synergistic interactions between the individual components. It is concluded that cobalt ions in combination with a metallic phase are important for oxygenate synthesis. Since it appears that the metallic phase can be pure cobalt, an important role for copper may be to moderate the hydrogenation and hydrogenolysis activity of metallic cobalt in order to enhance the selectivity for the formation of oxygenates at the expense of hydrocarbons.