A new TiO2-attached rhodium metal catalyst. Catalyst characterization and non-SMSI behaviour

Abstract

TiO₂-attached Rh metal cluster catalysts have been prepared by the reaction between Rh(η³-C₃H₅)₃ and surface OH groups of TiO₂, followed by H₂ treatments at different temperatures. This class of Rh/TiO₂ catalysts, which are very active for ethene hydrogenation and ethane hydrogenolysis, show no SMSI phenomena, unlike conventional Rh/TiO₂ catalysts prepared by a traditional impregnation method using aqueous RhCl₃. The structural properties of these catalysts, such as a shortening of the Rh–Rh distance, their raft-like structure and their positively charged character, have been studied in relation to non-SMSI behaviour by means of EXAFS together with other physiochemical techniques. These properties of structure, electronic state, chemisorption and catalytic activity may be ascribed to the Rh—O—Ti bonds which are formed in during attachment of the Rh–allyl complexes onto TiO₂ and are partially retained after high-temperature H₂ reduction.