Standardization transformation of C-lignin to catechol and propylene

Abstract

Abstract Standardization transformation of lignin to high-value-added chemicals requires precise control of the reaction process based on the elaborate catalytic strategy design and lignin structure optimization. Here we report the selective and efficient preparation of bio-catechol and bio-propylene from the ideal C-lignin via a one-pot hydrogenolysis-dealkylation cascade catalysis. The optimized catalyst Ni/HY30 could orderly cleave the corresponding Cα/β–OAr bonds and Caryl–Calkyl bonds in the uniform benzodioxane units of C-lignin, which could directionally and selectively provide a 49 mol% yield of catechol and a 45 mol% yield of propylene from C-lignin under 200°C. Further techno-economic analysis and the life-cycle assessment confirmed the potential of this strategy in the CO2-neutral preparation of catechol and propylene. In addition, the control experiments, catalyst characterizations, spectra identification, and DFT calculations indicated that the 4-propenylcatechol primarily generated from the selective hydrogenolysis of C-lignin was the critical intermediate for the following dealkylation, and the side chain was delicately deconstructed via the Brönsted acid-mediated protonation, γ-methyl migration and Caryl–Calkyl scission pathway. Finally, the corresponding strategy design based on the concept of standardization transformation and mechanism revelation focusing on the cleavage of critical linkage bonds could provide guidance for further lignin depolymerization utilization.