Metal-Organic-Framework-Derived Copper Catalysts for the Hydrogenolysis of Lignin into Monomeric Phenols

Reductive catalytic fractionation (RCF) of lignocellulosic biomass has emerged as a leading biorefinery strategy. Herein, we present a copper-based catalyst (CuO/C) derived from a metal-organic backbone (HKUST-1) with enhanced catalytic performance for RCF of woody sawdust, which affords high yields of propyl and propanol end-chain monomeric phenols (15.5 wt % in softwoods and 46.7 wt % in hardwoods) via the C-O bond scission. A series of conifer beta-O-4 models and their deuterated analogues revealed that the synergistic action of CuO/C and hydrogen could effectively cleave aryl ether linkages. It was deduced that lignin alcoholysis led to partial alpha-OH etherification of the beta-O-4' units, which promoted the C-O bond breakage of C-a-OMe and C-beta-O, thus giving propanol phenolic compounds through the hydrogenation of coniferyl alcohol over the CuO/C catalyst. When both alpha- and gamma-OH of beta-O-4' motifs were meoxylated, the para-propyl phenolics were obtained through the scission of C-O linkages (C-alpha-OMe and C-beta-O), followed by the Cr-OMe cleavage of propenyl ethers and hydrogenation of propenyl phenols. We envision that this work may pave the way for the development of non-noble catalysts with high reactivity and selectively for lignin valorization.

Automated summary

In this study, a copper-based catalyst derived from a metal-organic backbone is presented for the reductive catalytic fractionation of woody sawdust, which offers high yields of propyl and propanol end-chain monomeric phenols. The catalyst is found to effectively cleave aryl ether linkages, promoting the conversion of lignin into valuable compounds.