The control of metal precursor mobilities as a variable in the preparation of supported Pt$z.sbnd;Ru bimetallic clusters: The use of ruthenocene

Abstract The preparation of silica supported Pt-Ru bimetallic catalysts using ruthenocene as the Ru precursor has been studied. The high volatility of ruthenocene requires the use of a sequential impregnation technique. A Pt/SiO 2 catalyst prepared by the impregnation of silica wih HZPtCI6 6H 2 O was impregnated with a solution of ruthenocene in benzene. The mobile Ru precursor phase was observed to diffuse across the support to surface Pt sites where it was rapidly reduced. The surface of the resulting bimetallic catalyst was enriched in Ru. A subsequent heat treatment resulted in diffusion of Ru into the bulk. When RuCl 3 · 3H 2 O was used as the Ru metal precursor in this sequential impregnation technique, separate Pt and Ru particles were formed. This is explained in terms of the strength of metal precursor-support interactions. The hydrogenation of benzene and the hydrogenolysis of propane were used as catalytic test reactions in order to probe the presence of dual metal sites. The reaction rate for the hydrogenation of benzene was observed to go through a maximum at a surface composition of between 60 and 80% Pt. The hydrogenolysis of propane was consistent with a requirement of a Ru ensemble consisting of a small number of Ru surface atoms.