Hydrocarbon synthesis from carbon monoxide and hydrogen on impregnated cobalt catalysts Part I. Physico-chemical properties of 10% cobalt/alumina and 10% cobalt/silica

Abstract

The physico-chemical properties of impregnated cobalt catalysts were found to depend on the nature of the support and on the temperature of pretreatment. The decomposition of dried 10% cobalt/alumina and 10% cobalt/silica in an inert gas was found to proceed in two steps (the crystal water evolution and the total decomposition of cobalt nitrate) . In a reducing atmosphere, the endothermic decomposition was accompanied by exothermic reduction of cobalt nitrate, and the whole process depended strongly on the nature of the support. On silica, the formation of cobalt surface compounds with the support was much more limited than on alumina. The amount of adsorbed carbon monoxide was found to increase with the temperature of calcination, while both the degree of cobalt reduction and the cobalt dispersion decrease. Carbon monoxide was found to be adsorbed in four different states on the 10% cobalt/alumina catalyst (linear forms on Co 2+, Co δ+ and Co 0, bridged form on Co 0). Their relative amounts depended on the temperature of pretreatment. Catalyst pretreatment with a carbon monoxide and hydrogen mixture under hydrocarbon synthesis conditions causes a certain modification of the metal surface which leads to variations of the carbon monoxide adsorption states.