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

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 CoOx through an in situ transformation of the bimetallic RhCo NPs on SiO2. Among the obtained Rh-CoOx/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 CoOx 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 CoOx, however, would cause deactivation due to the less exposure of the Rh-CoOx interface.