Synergetic Catalysis of Nickel Oxides with Oxygen Vacancies and Nickel Phosphide for the Highly Efficient Hydrodeoxygenation of Phenolic Compounds

The highly efficient hydrodeoxygenation of oxygenated chemicals at a low temperature is a critical issue for biomass crude oil upgrading to reduce equipment and operation expense. The unique electronic features of oxygen vacancies have been found to facilitate deoxygenation above 250 degrees C. In this work, a series of NiOx/SiO2 catalysts that contain oxygen vacancies was prepared by a sol-gel and controllable temperature-programmed reduction method. Results show that NiOx/SiO2 has a superior phenol hydrogenation activity in deoxygenation even at 180 degrees C to Ni2P/SiO2. The high hydrogenation activity derives from the flat adsorption of phenolics over low-valence Ni cations induced by connected oxygen vacancies. After the introduction of NiOx into Ni2P catalysts, composite NiOx-Ni2P/SiO2 (0.43 <= x<1) bifunctional catalysts demonstrate better phenol hydrodeoxygenation performances under mild reaction conditions in comparison with individual Ni2P and NiOx catalysts and most catalysts presented previously because the coexistence of oxygen vacancies from NiOx and the acidity induced by Ni2P results in the synergistic effect of the adsorption configuration and hydrodeoxygenation ability. Besides, this composite catalyst also has a high activity for the hydrodeoxygenation of different bio-derived cresol isomers. The reuse test results confirm that oxygen vacancies are relatively stable in comparison with the phosphide.