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

Abstract

Self-hydrogen transfer hydrogenolysis (STH) has emerged as an effective approach for lignin depolymerization to phenolics due to its high atomic and energy efficiency. However, the development of a non-noble and efficient catalytic system remains a pivotal challenge. Herein, we report a facile and non-noble skeletal CuZnAl catalyst for the 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 a N₂ atmosphere. STH of organosolv lignin provided a 56 wt% lignin oil, with 30 wt% identified as aromatic monomers at 200 °C. Catalyst characterization and mechanistic studies revealed that Cu⁰ sites and oxygenated metal species on the catalyst's surface synergistically contributed to the dehydrogenation of hydroxyl groups and the cleavage of C–O bonds in lignin. A trace amount of water was revealed to promote the hydrogenolysis of the C–O bond through the protonation of O atoms in the C–O linkage. This current work provides a new and practical catalytic method for the STH of lignin, which adds to the catalyst family for lignin depolymerization and also holds great potential for industrial application.