Mechanistic Study of CTAB-Promoted C-O Bond Cleavage in β-O-4 Lignin Model Compounds

In the hydrogenolysis of lignocellulosic biomass, lignin depolymerization typically suffers from low efficiency, numerous side reactions, and reduced product yields. This study innovatively proposes a new strategy that selectively promotes the cleavage of lignin β-O-4 bonds by constructing a reverse micellar nanoreactor based on the cationic surfactant cetyltrimethylammonium bromide (CTAB), thereby enhancing the hydrogenolysis efficiency of lignin model compounds. A systematic investigation was conducted on the promotional effect of CTAB under conventional Ni/Al2O3 catalysis and non-polar solvent conditions. Experimental results demonstrate that the introduction of CTAB significantly increased the total yield of the lignin model compound 2-phenoxy-1-phenylethanol (PP-ol) depolymerization to 69.60%, enhanced monomer yield by 1.39 times, and improved ethylbenzene selectivity by 4.67 times. CTAB effectively suppressed excessive hydrogenation of the benzene ring and polymerization side reactions. Combined with molecular dynamics (MD) simulations and ¹H NMR characterization, three aspects of CTAB's promotion in non-polar solvents (such as n-hexane) were revealed: (1) within the core of the reverse micelle, the positively charged quaternary ammonium group interacts electrostatically and forms hydrogen bonds with the ether oxygen and hydroxyl groups of PP-ol, activating the C-O bond; (2) reaction products are influenced by the electrostatic and polarity effects of the reverse micelle structure, effectively inhibiting condensation reactions of intermediates such as ethylbenzene; (3) the reverse micelle reduces the system's surface tension, facilitating the formation of hydrogen microbubbles, thereby significantly improving hydrogen solubility and mass transfer efficiency in the non-polar medium. This strategy provides new theoretical support for designing biomass catalytic conversion systems that are efficient, highly selective, and resistant to carbon deposition.