STUDY OF THE PHYSICOCHEMICAL MECHANISMS INVOLVED DURING THE PREPARATION OF NI/SIO2 CATALYSTS BY DEPOSITION-PRECIPITATION

The preparation method of Ni/SiO2 catalysts by deposition-precipitation is based on the precipitation of nickel onto silica by an homogeneous increase in the hydroxyl ion concentration arising from urea hydrolysis. The study of the influence of the preparation parameters shows that the nature of the supported NI(II) phase results from a kinetic competition between two reactions: i) the Ni-Ni polymerization leading to the formation of nickel hydroxide, ii) the Ni-Si copolymerization leading to the formation of 1:1 nickel phyllosilicate. The kinetics of phyllosilicate formation is controlled by the si!lca dissolution rate.