Reductive catalytic fractionation (RCF) of lignocellulosic biomass has demonstrated as an efficient strategy to produce aromatic compounds from lignin. Herein, we present a Cu-based catalyst (CuO/C) derived from a metal–organic framework (Cu-MOF) which exhibits enhanced catalytic performances for RCF of woody sawdust, affording monomeric phenols in high yields (up to 15.5 wt% in softwood and 41.8 wt% in hardwood). This catalyst shows high selectivity toward phenolic compounds with propyl and propanol end chains. The effects of some key parameters such as the influence of solvent, hydrogen pressure, temperature, reaction time and catalyst dosage were examined in view of monomer yield and average molecular weight. Using a series of dimeric, trimeric, and polymeric β-O-4 lignin motif, as well as deuterated analogues, we further report an in-experimental study on the mechanism of CuO/C catalyzed hydrogenolysis of lignin. We deduced that the solvolysis of lignocellulose led to partially α-meoxylated β-O-4 motif, which facilitated C−O bond cleavage of Cα-OMe and Cβ-O, thus giving propanol phenolic compounds through hydrogenation of monolignols over CuO/C catalyst. When both α- and γ-OH of β-O-4 motif were meoxylated, the para-propyl phenolics were obtained though the scission of C−O linkages (Cα-OMe and Cβ-O), followed by Cγ-OMe cleavage of propenyl ethers and hydrogenation of propenyl phenols. We envision that this work may pave the way for the development of novel non-noble catalyst with high reactivity and selectively for lignin valorization.

Metal–organic framework derived copper catalysts for efficient hydrogenolysis of lignin into monomeric phenols

ACS Spring 2022

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