Highly selective conversion of phenol to cyclohexanol over increased acidity on the Ru/Nb2O5-nC18PA catalysts in biphasic system under mild condition

Cyclohexanol is an essential intermediate in the chemical industry for the synthesis of nylon and other materials, but the direct hydrogenation of phenol to produce cyclohexanol is problematic due to excessive energy consumption associated with the harsh reaction conditions. In this regard, the novel composite catalysts (Ru/Nb2O5-nC18PA) coated with octadecylphosphonic acid (C18PA) was prepared via an impregnation method to be applied for the efficient hydrogenation of phenol to produce cyclohexanol in the biphasic system consisting of water and decalin solvent. Under a hydrogen pressure of 12 bar and 80 °C, nearly 100% conversion of phenol and 93% yield of cyclohexanol are achieved within 4 hours. With the introduction of more Lewis acid sites the aromatic ring is activated which promotes the HYD (hydrogenation) path of phenol, thereby giving an improved selectivity to cyclohexanol. A mechanism exploration experiment was carried out and showed that the strong binding effect between the surface of the Ru/Nb2O5-nC18PA catalysts and the benzene ring allows the aromatic ring in phenol to be hydrogenated increasing the selectivity to cyclohexanol. This biphasic catalytic system enhances the potential value of lignin via the catalytic hydrogenation of lignin-derived phenols.