High-Efficiency Lignin Depolymerization to Aromatic Monomer Over Zif-67@Biochar Catalyzed Β-O-4 Bond Cleavage in Water Medium

Abstract

High-efficiency lignin conversion to high value-added aromatic monomer faced huge challenges due to the complexity of the lignin structure. Here in, focusing on the biomass comprehensive utilization, a highly-efficient biochar supported ZIF-67 (ZIF-67@Biochar) was constructed to convert β-O-4 type lignin to high value-added aromatic aldehydes/ketone. The vanillin, acetovanillone and trace other small aromatic compounds were yielded at 8.05%, 2.28% and 2.73% respectively, which indicating the 84.26% monomers recovery obtained. The abundant carbon defect, high BET specific surface area and surface functional groups in biochar synergetic promote the highly efficient lignin depolymerization. Molecular electrostatic potential surface (MEPS) was used to investigate the adsorption activation of ZIF-67 for β-O-4 bonds based on the electrostatic potential (ESP). By employing 2D-HSQC-NMR and on-line FT-IR, the cleavage of Cα-Cβ and Cβ-O bonds in β-O-4 during lignin depolymerization was investigated in-deepthly. The bond dissociation enthalpy (BDE) of Cβ-O bond was reduced as the Cα=O intermediate formation, thus further causing the Cα-Cβ bond to cleave under retro-aldol reaction.

Keywords: lignin, ZIF-67@Biochar, vanillin, 2D-HSQC-NMR, on-line FT-IR