Sustainable production of C6 phenols from lignin via sequential C O and C C bond cleavage over Ni-MgO/hydroxyapatite catalyst

Abstract

Lignin, the only renewable source of aromatic compounds, remains underutilized due to its structural complexity. Self-supplied hydrogenolysis (SSH), which leverages endogenous hydroxyl groups as hydrogen donors, has emerged as a promising strategy for lignin valorization. However, conventional SSH predominantly yields C8/C9 alkylphenols rather than the more valuable C6 phenols due to rapid catalyst-driven hydrodeoxygenation. Here, we report a carbonyl-stabilization strategy using a non-noble Ni–MgO/hydroxyapatite (HAP) catalyst that enables sequential cleavage of C β -O and C 1 -C α bonds, achieving 74.4 % selectivity for C6 phenolic monomers. Mechanistic studies reveal that basic sites on MgO/HAP facilitate oxygen adsorption at C α sites, promoting Ni-catalyzed C α H–OH dehydrogenation to C α = O groups, which lowers the dissociation energy of C β –O bonds, enabling efficient cleavage. Furthermore, the limited hydrodeoxygenation activity of Ni–MgO/HAP stabilizes C8/C9 carbonyl intermediates, allowing C 1 -C α bond scission via high-temperature hydrogen-driven carbocation formation. This strategy represents a paradigm shift in lignin depolymerization, offering a direct, hydrogen-efficient route to C6-based platform chemicals. By maximizing lignin-derived product value while reducing reliance on external hydrogen, this work advances sustainable biomass conversion and green chemical manufacturing. • Lignin is selectivity converted into C6 phenols via carbonyl-stabilization strategy during self-supplied hydrogenolysis. • Nickel promotes the dehydrogenation of C α H-OH groups, aided by basic sites on MgO/hydroxyapatite (HAP). • Mg doping increases the number of basic sites and enhances the availability of Ni 0 active sites on the catalyst surface. • Low-loading Ni stabilize the C8/C9 carbonyl-containing phenolic intermediates by preventing over-hydrogenation. • High-temperature hydrogen protons facilitate the activation and cleavage of C 1 -C α bonds.