Double-active site synergistic catalysis in Ru–TiO2 toward benzene hydrogenation to cyclohexene with largely enhanced selectivity

Abstract

The selective hydrogenation of benzene is one promising route to obtain cyclohexene, a key intermediate for the production of various value-added fine chemicals. Herein, we report the preparation of a novel Ru/TiO₂ catalyst encapsulated by a porous TiO₂ coating (denoted as (Ru/TiO₂)@p-TiO₂) for this reaction, in which the supported Ru particles serve as active sites for hydrogen dissociation while the porous TiO₂ surface acts as the active center for benzene hydrogenation. By virtue of the shielding effect of the porous TiO₂ layer with a suitable pore size, only hydrogen molecules can diffuse into the interior Ru surface for dissociation adsorption, followed by hydrogen spillover from Ru to the porous TiO₂ surface and subsequent hydrogenation of adsorbed benzene there. Cyclohexene temperature programmed desorption (CHE-TPD) and DFT calculations demonstrate that cyclohexene shows a more beneficial desorption and a much higher activation energy for its further hydrogenation over the TiO₂ surface in comparison with the Ru surface, accounting for the largely enhanced catalytic performance (benzene conversion: 98.1%, cyclohexene selectivity: 76.6%). This double-active-site synergistic catalysis, to the best of our knowledge, gives the highest cyclohexene yield ever reported.