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

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.