Tailoring the activity and selectivity of Rh/SiO2 for the selective hydrogenation of phenol by CoOx promotion

Abstract

Although supported Rh nanoparticles (NPs) are one of the best catalysts for the selective hydrogenation of phenol to cyclohexanol, they still suffer from poor selectivity problems. In this study, we promoted the selectivity of Rh NPs with CoO_x through an in situ transformation of the bimetallic RhCo NPs on SiO₂. Among the obtained Rh–CoO_x/SiO₂ catalysts, the one with a Co/Rh molar ratio of 1/3 exhibited the highest phenol conversion (i.e., 98.1%) and the highest selectivity to cyclohexanol (i.e., 99.4%). Our study showed that CoO_x promoters modified the electronic states of Rh and created new active sites at their interface, which are beneficial to the activation of phenol and the desorption of cyclohexanol. Excessive coverage of Rh by CoO_x, however, would cause deactivation due to the less exposure of the Rh–CoO_x interface.