TPR study on the preparation of impregnated Co/SiO2 catalysts

During the preparation of impregnated cobalt on silica catalysts, different Co-species are formed and these can be detected by means of temperature programmed reduction (TPR). The impregnation step can be explained in terms of interfacial coordination chemistry. During the impregnation step, the precursor of surface cobalt silicate is formed by a reaction between surface silanol groups and aqueous cobalt complexes. Therefore, the choice of solvent used in the impregnation step, of the metal salt, and of the carrier is of great importance in the degree of reduction that can be achieved at normal reduction temperatures and catalyst dispersion. Decreasing the polarity of the solvent increases the amount of surface cobalt silicates in the catalyst since the interaction between silanol groups and the cobalt aquocomplex is favored. If the pH of the impregnation solution is above 5 (e.g., using cobalt acetate as the cobalt salt) more cobalt silicates are formed. Drying or low-temperature calcination destroys the precursor of the surface cobalt silicate. (C) 1996 Academic Press, Inc.