Influence of metal–support interactions on the hydrogenolysis of methylcyclopentane over supported Rh catalysts

Abstract

Titania- and silica-supported Rh catalysts have been prepared, pretreated in various ways and their activity and selectivity for the hydrogenolysis of methylcyclopentane determined. Over Rh/silica catalysts the major products are 2-methylpentane and 3-methylpentane. When Rh/titania catalysts are reduced at low temperatures the product distribution differs from that obtained over Rh/silica. More n-hexane is formed and the temperature dependence of the product distribution is different. The results provide evidence of a real support effect. The most remarkable result obtained is that after reduction of the titania-supported catalysts at high temperatures, which leads to a suppression of hydrogen adsorption due to contamination of the Rh by TiO_x, the activity of the Rh remains high. The product distribution, in contrast, is only slightly modified. When the catalyst reduced at high temperature is partially oxidised by exposure to oxygen at 298 K ca. 50% of the Rh surface is freed from contamination. However, the activity and turnover numbers decrease as a result of this treatment. It is concluded that only a small fraction of the surface Rh atoms have high turnover numbers for the methylcyclopentane reaction. It is suggested that the active centre is a small Rh ensemble (1 or 2 Rh atoms) in a planar surface.