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

Abstract

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 % in the absence of additional hydrogen pressure. 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.