Abstract
Physicochemical characterization of calcined and sulfided CoO/SiO{sub 2} catalysts were carried out to reveal the interaction modes between cobalt and SiO{sub 2} using XPS, TPR, TEM, DRS-VIS, and XRD techniques. The CoO/SiO{sub 2} 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/SiO{sub 2}. These species are assigned to Co{sub 3}O{sub 4}, Co-Si-O mixed oxide, surface Co{sup 3+} species, surface silicate, surface Co{sup 2+} 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/SiO{sub 2} catalysts with a uniform distribution of cobalt species throughout the catalyst particles as compared to conventionally employed cobalt nitrate. The proportion of Co{sup 3+} greatly decreases when cobalt acetate was used instead of cobalt nitrate. All the cobalt species interacting with SiO{sub 2} were found to be sulfided at 673 K.
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