Support effects on selectivity over rhodium bimetallic catalysts

Abstract

Rhodium catalysts are about one order of magnitude more active for ethane hydrogenolysis when supported on alumina or titania than when supported on silica when reduction is carried out at low temperature. However, the difference in activity for ethane hydrogenolysis between low-(573 K) and high-(773 K) temperature reduced Rh on titania is much greater. When the selectivity between dehydrogenation and hydrogenolysis of cyclohexane is compared at low and high temperature, a modest increase in selectivity is found to accompany the increased reduction temperature. A more substantial effect on selectivity is evident when Rh–Ag on silica and titania, both reduced at low temperature, are compared. The direct effect of rhodium–titania interaction (varied reduction temperature) and the indirect effect of support (changed Rh–Ag interaction) appear to have a common origin. It is proposed that in both the direct and indirect support interactions there may be preferential interaction with the smallest particles in the distribution.