Preparation of Defective Niobium-Based Catalysts to Address the “Seesaw Effect” in Phenol Hydrodeoxygenation

Cyclohexanone, a product of phenol hydrogenation, is a very reactive intermediate, which can easily generate byproducts such as cyclohexanol and cyclohexane, and there is a difficult-to-regulate “seesaw effect”. In this paper, a defective catalyst, Pd/Nb2O5-800-AP, was synthesized by the hydrothermal method at 170 °C and 1 MPa H2, aiming to break the difficult equilibrium between the high conversion of phenol and the high selectivity of cyclohexanone, which has a good industrial prospect. By changing the calcination temperature of the carrier to control the surface defect content, Pd was placed in an electron-rich state, which promoted the activation of hydrogen molecules and adsorption of phenol in a “nonplanar” manner, which was favorable for the generation of cyclohexanone as a product. In addition, the formation of electron-deficient oxygen defects and low-valent Nb4+ on the surface of the AP-treated catalysts promoted the adsorption and activation of oxygen-containing functional groups, which enhanced the activity of the phenol HDO reaction.