ACTIVATION OF A SILICA-SUPPORTED NICKEL-CATALYST THROUGH SURFACE MODIFICATION OF THE SUPPORT

The activity of a nickel/silica catalyst in benzene hydrogenation was markedly promoted only by the calcination of the support at 400-850°C before impregnation of nickel nitrate in water. The promotional effect was also observed for catalysts prepared from the same nickel salt in acetone and ethanol. This promotion of nickel catalysts was ascribed to an increased degree of nickel dispersion. The calcination of the support influenced the deposition of nickel precursors; a higher degree of precursor dispersion was achieved on calcined, dehydrated silica supports, resulting in an increase in nickel dispersion after reduction, than was achieved on an uncalcined one. In addition, the rehydration of a calcined silica support led to a decrease in the nickel dispersion. Interestingly, the density of surface hydroxyl groups of the supports was correlated with the degree of nickel dispersion, higher nickel dispersion being achieved with lower density of these functional groups. Possible reasons for the observed promotional effects of the silica calcination are discussed, focusing attention on its surface hydroxyl groups. © 1990.