Preparation of silica-coated Pt metal nanoparticles using microemulsion and their catalytic performance

Pt-SiO2 catalysts were prepared by using water-in-oil type microemulsion. The catalysts were prepared by hydrolysis of tetraethylorthosilicate in the microemulsion containing Pt species, followed by calcination in air and reduction with H-2. This preparation method for Pt-SiO2 provided Pt metal nanoparticles with a diameter of ca. 6nm covered uniformly with silica layers, while a conventional impregnation method formed Pt metal particles supported on the silica surface. The Pt catalysts coated with silica (coat-Pt) showed different catalytic performance for the competitive oxidation of mixed hydrocarbons from Pt catalysts supported on silica (imp-Pt), i.e. in the competitive oxidation of methane and iso-butane, coat-Pt catalysts preferentially oxidized methane, while iso-butane was oxidized selectively over imp-Pt catalysts. The results of the adsorption of Ar on coat-Pt showed that silica in coat-Pt had porous structures of pore diameters < I nm. Because the porous structure of silica, which wrapped Pt metal particles, controlled the diffusion rate of reactant molecules, coat-Pt showed a specific catalytic performance for competitive oxidation. (c) 2006 Published by NIMS and Elsevier Ltd.