Enhanced Effect of Carbon for the Ni/T-Nb2O5 Catalyst on Vanillin Hydrodeoxygenation in the Aqueous Phase

The aqueous hydrodeoxygenation (HDO) of renewable biomass is an effective method to produce alternative fuels and high-value-added chemicals. Nonetheless, metal leaching and support collapse are the main obstacles in aqueous HDO. Herein, a series of Ni/T-Nb2O5@C catalysts were successfully prepared for selective HDO of vanillin (a typical lignin-derived model compound). Characterization results revealed that the superior catalytic performance of Ni/T-Nb2O5@C catalysts was due to the efficient adsorption of the reactant preferentially via oxygen vacancies and the excellent selection of deoxygenated products via acid sites on the catalyst surface. Meanwhile, water can interact with vanillyl alcohol (VA) through hydrogen bonding to form a more stable transition state, further reducing the activation energy of the VA hydrogenolysis process and promoting the conversion of VA to 2-methoxy-4-methylphenol (MMP). Ni/T-Nb2O5@C2-2 catalyst exhibited excellent performance for vanillin HDO, achieving 99.9% conversion, 96.6% MMP selectivity, and 87.7% mass yield at 150 °C for 1 h, 1 MPa H2, and a water:ethanol ratio of 8:12, which greatly improved the MMP selectivity (79.2%) of unmodified Ni/T-Nb2O5 catalyst. Moreover, the catalyst had good catalytic capability after eight cycles of less than 25% conversion, and the retention of the initial active substance during the reaction was analyzed. This work may provide insights into the rational design of composite-supported catalysts for biomass-derived compounds HDO in the aqueous phase.