Facile depolymerization of lignin into phenolics via self-hydrogen transfer hydrogenolysis over skeletal CuZnAl catalyst

Abstract

Self-hydrogen transfer hydrogenolysis (STH) has emerged as an effective approach for lignin depolymerization to phenolics owning to its high atomic and energy efficiency, however, the development of non-noble and efficient catalytic system remains a pivotal challenge. Herein, we report a facile and non-noble skeletal CuZnAl catalyst for STH of lignin dimer 2-phenoxy-1-phenylethanol (α-OH-PPE). The reaction offered a 92% yield of acetophenone and a 92% yield of phenol at a mild reaction temperature of 160 °C under N₂ atmosphere. STH of organosolv lignin provided a 56 wt% lignin oil, with 30 wt% being identified as aromatic monomers. Catalyst characterization and mechanistic study revealed Cu⁰/Cu⁺ active sites and oxygenated metal species on catalyst’s surface synergistically contributed to dehydrogenation of hydroxyl group and cleavage of C-O bonds in lignin. A trace amount of water was revealed to promote the hydrogenolysis of C-O bond through the protonation of O atoms of C-O linkage. This current work provides a new and practical catalytic method for STH of lignin, which adds to the catalyst family for lignin depolymerization and also own great potential for industrial application.