Ni/Ce co-doping metal-organic framework catalysts with oxygen vacancy for catalytic transfer hydrodeoxygenation of lignin derivatives vanillin

Exploring an advanced catalytic strategy for the high value utilization of lignin derived chemicals into value-added aromatics has attracted tremendous sights for green manufacturing. In this paper, a series of bifunctional 3D rod-shaped mesoporous NiCe metal-organic framework catalysts coupling with hydrogen-donner solvent were reported for the hydrodeoxygenation of vanillin to obtain 2-methoxy-4-methylphenol. Under the optimal conditions, 3Ni-Ce/C catalyst realized the highest conversion of vanillin (>95.0%) and selectivity of 81.4%. The characterization results indicated that the interaction of metallic Ni and CeO2 promoted the generation of Ni-CeO2-x interface and oxygen vacancies (Ov), which could efficiently adsorb and activate aldehyde group of vanillin to obtain reactive intermediates. And then metallic Ni sites activated the hydrogen-donner solvent to form adsorbed H atoms, which then spilled over to the adjacent Ov to stabilized reactive intermediates. Whereafter, bifunctional 3D rod-shaped mesoporous NiCe metal-organic framework catalysts achieved the hydrodeoxygenation upgrading of vanillin to obtain 2-methoxy-4-methylphenol. Density functional theory (DFT) calculations further revealed that the synergistic effect of Ni-CeO2 and oxygen vacancies promoted the activation and dissociation of aldehyde group bond in vanillin, enhanced the ability of protonation hydrogenolysis. Additionally, 3Ni-Ce/C catalyst displayed robust activity for no less than four recycles, which provided a feasible method for the build of simultaneous utilization of lignin derivates to value-added fuels and chemicals.