PREPARATION AND CHARACTERIZATION OF HIGHLY DISPERSED COBALT OXIDE AND SULFIDE CATALYSTS SUPPORTED ON SIO2

Physicochemical characterization of calcined and sulfided CoO/SiO2 catalysts were carried out to reveal the interaction modes between cobalt and SiO2 using XPS, TPR, TEM, DRS-VIS, and XRD techniques. The CoO/siO2 catalysts were prepared by an impregnation method using cobalt acetate as well as cobalt nitrate and by an ion-exchange technique. It was found that several kinds of cobalt species are formed on CoO/SiO2. These species are assigned to Co3O4, Co-Si-O mixed oxide, surface Co3+ species, surface silicate, surface Co2+ species in the order of the TPR reduction temperature. Their proportions strongly depended on the starting salt, cobalt content, and preparation method. Cobalt acetate was found to provide highly dispersed CoO/SiO2 catalysts with a uniform distribution of cobalt species throughout the catalyst particles as compared to conventionally employed cobalt nitrate. The proportion of Co3+ greatly decreased when cobalt acetate was used instead of cobalt nitrate. All the cobalt species interacting with SiO2 were found to be sulfided at 673 K. It was demonstrated that sulfided CoO/siO2 catalysts prepared from cobalt acetate show several times higher hydrogenation activity than the catalysts from cobalt nitrate. On the basis of the XPS characterization of uncalcined precursors, the effects of starting salt on the cobalt-SiO2 interaction modes and cobalt dispersion and distribution are discussed.