Lignin-derived cage-like hollow carbon sphere for the catalytic hydrodeoxygenation of vanillin

Abstract

Taking advantages of the structural features of lignin for its functionalization application benefits to develop a sustainable lignin biorefinery process. Herein, cage-like hollow carbon sphere (LC) with high stability and reducibility was fabricated by spray drying and controlled carbonization, due to the high content of carbon element and abundant phenolic hydroxyl groups of lignin. Spray drying would induce the self-assembly of lignin during solvent evaporation, and the introduction of KOH in this process increased the specific surface area of LC and created more surface defects. The controlled carbonization led to the cross-linking of lignin and partly retained the lignin polyphenolic structure, which could be used to adsorb and in situ reduce Pd^2 + to prepare Pd/LC catalyst. Owing to the synergistic catalytic effect of the abundant defect sites on the LC surface and the active Pd sites, the Pd/LC catalyst could catalyze the hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol under mild reaction conditions (90 °C, 1.5 h, 0.5 MPa H₂). Besides, the catalyst showed high activity after four cycles and universality for the other lignin-derived aromatic aldehydes.