Synergistic Ru–Ni Nanoparticles on Oxygen-Vacancy-Rich and Acidic CeO2 for Efficient Catalytic Hydrogenolysis of Lignin and Its Model Compounds under Mild Conditions

A promising strategy for lignin valorization is catalytic hydrogenolysis (CH) of C–O or C–C bridging bonds over supported metal catalysts to produce aromatics. Herein, a bimetallic RuNi/CeO2 catalyst was developed via impregnation and evaluated for CH of alkali lignin and its model compounds. Comprehensive catalyst characterizations confirmed the strong synergistic Ru–Ni nanoparticles, abundant oxygen vacancies (Ov), and moderate-to-strong acid sites on RuNi/CeO2. It achieved 100% conversion of benzyl phenyl ether (BPE) under mild conditions (100 °C and 1.5 MPa H2) with toluene and phenol as the main products, markedly outperforming monometallic counterparts. It also exhibited excellent performance for other α-O-4 and β-O-4 model compounds under moderate conditions of 180 °C and 0.5 MPa H2, affording aromatic monomers as the dominant products. Mechanistic studies indicated that RuNi/CeO2 cooperatively activates H2 and isopropanol to generate hydrogen radicals (H•) and protons (H+), facilitating selective cleavage of C–O bonds. Applied to alkali lignin, CH over the catalyst produced a 41.1 wt % lignin oil, with phenols constituting over 70% of the liquid products, underscoring its efficacy in real lignin conversion. This work provides an efficient and selective catalytic strategy for lignin valorization, contributing to the sustainable production of valuable aromatics in the biorefining industry.