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

The preparation method of Ni/SiO2 catalysts by deposition-precipitatio n is based on the precipitation of nickel onto silica by an homogeneou s increase in the hydroxyl ion concentration arising from urea hydroly sis. The study of the influence of the preparation parameters shows th at the nature of the supported NI(II) phase results from a kinetic com petition between two reactions: i) the Ni-Ni polymerization leading to the formation of nickel hydroxide, ii) the Ni-Si copolymerization lea ding to the formation of 1:1 nickel phyllosilicate. The kinetics of ph yllosilicate formation is controlled by the si!lca dissolution rate.