Identification of nickel species and their interaction with the support in Ni-silica catalyst precursor

Abstract

Precipitates of basic nickel carbonate were prepared in the presence of silica slurry at varying SiO 2/Ni ratios using a coprecipitation method. The nickel was found to be present as: (i) basic nickel carbonate (soluble in NH 4Cl/NH 4OH solution); and (ii) nickel hydrosilicate species (insoluble in NH 4Cl/NH 4OH solution). The nickel which is reducible at 400 °C matches with the nickel present in basic nickel carbonate species. Infrared, thermal and TPR studies clearly demonstrate that it is not the silica but the nickel hydrosilicate containing -Ni-O-Si- linkages that acts as the ‘support’ to basic nickel carbonate species. Reduction behaviour and SiO 2/Ni ratios were identical for the ‘support’ species obtained from parent precursors of varying SiO 2/Ni ratios. The fatty acid hydrogenation activity of reduced parent precursors passes through a maximum at SiO 2/Ni = 0.5, where stability of the nickel particle and accessibility of the nickel surface to reactant molecules were at an optimum.