Tailoring the activity and selectivity of Rh/SiO for the selective hydrogenation of phenol by CoO 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 CoO x through an in situ transformation of the bimetallic RhCo NPs on SiO 2 . Among the obtained Rh-CoO x /SiO 2 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. The CoO x promoted Rh/SiO 2 catalyst, with a Co/Rh ratio of 1/3, had the highest activity ( i.e. , a phenol conversion of 98.1%) and selectivity to cyclohexanol ( i.e. , 99.4%), due to the formation and maximum exposure of the active Rh-CoO x interfaces.