Metal–Organic-Framework-Derived\nCopper Catalysts\nfor the Hydrogenolysis of Lignin into Monomeric Phenols

Abstract

Reductive catalytic fractionation (RCF) of lignocellulosic\nbiomass\nhas emerged as a leading biorefinery strategy. Herein, we present\na copper-based catalyst (CuO/C) derived from a metal–organic\nbackbone (HKUST-1) with enhanced catalytic performance for RCF of\nwoody sawdust, which affords high yields of propyl and propanol end-chain\nmonomeric phenols (15.5 wt % in softwoods and 46.7 wt % in hardwoods)\nvia the C–O bond scission. A series of conifer β-<i>O</i>-4 models and their deuterated analogues revealed that\nthe synergistic action of CuO/C and hydrogen could effectively cleave\naryl ether linkages. It was deduced that lignin alcoholysis led to\npartial α-OH etherification of the β-<i>O</i>-4′ units, which promoted the C–O bond breakage of\nC_α-OMe and C_β-O, thus giving propanol\nphenolic compounds through the hydrogenation of coniferyl alcohol\nover the CuO/C catalyst. When both α- and γ-OH of β-<i>O</i>-4′ motifs were meoxylated, the para-propyl phenolics\nwere obtained through the scission of C–O linkages (C_α-OMe and C_β-O), followed by the C_γ-OMe cleavage of propenyl ethers and hydrogenation of propenyl phenols.\nWe envision that this work may pave the way for the development of\nnon-noble catalysts with high reactivity and selectively for lignin\nvalorization.