Supported rhenium nanoparticle catalysts for acceptorless dehydrogenation of alcohols: structure–activity relationship and mechanistic studies

Abstract

Al₂O₃-supported Re with different oxidation states and Re⁰ metal nanoparticles on various supports are prepared, characterized and tested for the dehydrogenation of 2-octanol. The activity of Re/Al₂O₃ increases with the fraction of metallic Re. The activity of metallic Re depends on the support oxides, and the support with moderate electronegativity (Al₂O₃) gives the highest turnover frequency (TOF) per surface Re⁰ site. Re/Al₂O₃ is effective for acceptorless dehydrogenation of various aliphatic secondary alcohols to ketones. The kinetic isotope effects on the dehydrogenation of 2-propanol show that dissociation of the α-C–H bond of 2-propanol is the rate-limiting step. The IR study of the reaction of gas phase 2-propanol over the Re/Al₂O₃ surface shows that the acid–base pair site of Al₂O₃ is responsible for the O–H dissociation of 2-propanol. The structural requirements are discussed on the basis of the mechanistic results.