The influence of metal-support interactions on the reaction of n-hexane over supported Rh catalysts

Abstract

Rh catalysts have been prepared by impregnation of silica or titania and their activities and selectivities determined for the reaction of n-hexane. Titania-supported Rh catalysts are more active than silica-supported and have a different selectivity for isomerization being much less selective for the formation of 2- methylpentane. The results provide evidence of a real support effect even in catalysts reduced at low temperatures. When the Rh/titania catalysts are reduced at high temperatures to induce “Strong Metal-Support Interactions” the turnover number is increased but the selectivity and product distribution are unaffected. When the SMSI Rh/titania catalysts are re-oxidized at 298 K to partially reverse the SMSI state the turnover number decreases by more than two orders of magnitude, but the selectivity does not change. It is concluded that although SMSI catalysts behave differently from “normal” Rh/titania catalysts the creation of the SMSI state is not a prerequisite for obtaining high activity or unusual selectivity. A model is presented in which the active centres for the n-hexane reaction are considered to be Rh atoms in flat surfaces. The reforming of hydrocarbons is a process of major industrial importance. The results obtained demonstrate that metal-support interactions can affect the selectivity of a metal in reforming reactions and provide information on the nature of the active centre required for the skeletal rearrangement of hydrocarbons.