FORMATION OF METALLIC PARTICLES DURING TEMPERATURE-PROGRAMMED REDUCTION OF SILICA-SUPPORTED PLATINUM AND NICKEL CHLORIDES

The formation of (bi-) metallic particles during temperature-programmed reduction of silica-supported mixtures of Pt and Ni chlorides was followed by X-ray absorption spectroscopy. The concentration and composition of the metal particles in the final catalysts were derived from the results of the EXAFS analysis. The reduction kinetics followed by XANES were related to the formation of ordered metallic phases. During temperature-programmed reduction, most of the bimetallic phase was formed simultaneously with the reduction of the catalyst precursor. The bimetallic catalysts consisted of at least one bimetallic phase and of the pure phase of the metal in excess. For catalysts containing more than 50 atom % Ni, we concluded that there was either an enrichment of the bimetallic phase in Ni or the formation of a second bimetallic phase (Ni3Pt). For catalysts containing 50 atom % Ni or less we concluded that the stoichiometric NiPt phase was the only bimetallic phase.