NUCLEATION AND PARTICLE GROWTH IN THE PREPARATION OF SILICA-SUPPORTED NICKEL-CATALYSTS BY A 2-STEP PROCEDURE

The mechanism of nucleation and growth of particles in the preparation of supported catalysts has been investigated in the case of the Ni/SiO2 system. The separation of this two-step mechanism is achieved as follows: i) the "nickel nuclei" are prepared by ion-exchange or by impregnation followed by washing. They are in strong interaction with the support and act as anchoring sites for the metal particles. ii) The "nickel reservoir" constituted of nickel ion precursors and necessary for the nickel particle growth on the nuclei, is deposited by impregnation on the support. It is in weak interaction with the support and easily reducible. After temperature programmed reduction of the samples prepared by the above two-step procedure, the nickel particles are smaller and more homogeneous in size than those of catalysts prepared in one step by single impregnation of a pure silica support.