Exchange reactions of hydrocarbons on silica-supported Rh–Pt bimetallic catalysts

Abstract

A series of silica-supported rhodium–platinum catalysts containing 10^–4 mol metal g^–1 silica have been shown to be well dispersed by temperature-programmed reduction. Exchange reactions with deuterium of methane (463 K), 2,2-dimethylpropane (323 K) and n-butane (311 K) were followed using most of the catalysts in the series. Two patterns of activity against composition curve were found. For methane and 2,2-dimethylpropane, i.e. molecules containing only primary C—H bonds which cannot form α,β-diadsorbed species, platinum was as effective if not more effective than rhodium. However, for the exchange of n-butane (and also propane) rhodium was some 20–30 times more active than platinum. The extent of multiple exchange increased with rhodium content. There was some evidence for the importance of electronic effects from the variations of activity and selectivity with metal composition.