Synergistic Effect of Lewis Acidity and Metal Electronegativity in Ni/C@N Catalyst Enabling Hydrogen-Free Lignin Hydrogenolysis

Abstract

Self-hydrogen-supplied hydrogenolysis (SHSH) presents an atom-economical strategy for lignin depolymerization by utilizing intrinsic hydroxyl groups as internal hydrogen donors. However, the high activation energy associated with C_α–OH dehydrogenation typically requires noble-metal catalysts or harsh conditions, limiting the practical implementation of SHSH. Here, we report a nitrogen-doped, non-noble Ni/C@N catalyst that enables efficient SHSH under mild hydrothermal conditions (140 °C in water). Derived from the pyrolysis of urea-modified nickel metal–organic frameworks, the catalyst features electronegative Ni species and abundant Lewis acid sites, which work synergistically to lower the dehydrogenation barrier by facilitating O–H bond activation and hydrogen abstraction. This design achieves 97.2% dehydrogenation efficiency of C_αH–OH motifs and delivers a phenolic monomer yield of 35.9 wt % from native birch lignin. Kinetic analysis confirms C_αH–OH dehydrogenation as the rate-determining step, with an apparent activation energy of just 33.1 kJ mol^–1. The catalyst exhibits excellent recyclability and enables facile magnetic separation from products. These results establish a noble-metal-free, low-carbon route for lignin valorization and highlight a rational catalyst design strategy for overcoming key kinetic limitations in SHSH processes.