Support-Governed Acid-Redox Synergy in Molybdenum-Catalyzed Reductive Depolymerization of Lignin

Selective depolymerization of kraft lignin remains challenging because of its structural heterogeneity and the tendency of reactive fragments to undergo retrogressive condensation under N 2 without external H 2 . Here, Mo-based catalysts supported on SiO 2 , activated carbon, Al 2 O 3 , and H-Beta zeolite were evaluated for kraft lignin depolymerization in a 1,4-dioxane/isopropanol/methanol donor-solvent system at 290°C for 6 h under 0.5 MPa N 2 . Support identity strongly governed the balance between lignin fragmentation, intermediate stabilization, deoxygenation, and carbonaceous-deposit formation. Mo/H-Beta delivered the best overall performance, achieving 79.1% lignin conversion and 49.1% light-fuel yield, while increasing the light-fuelHHV from 25.45 to 36.01 MJ kg −1 . Although Mo/SiO 2 promoted the strongest molecular-weight reduction, it was less effective in downstream stabilization, and deoxygenation, demonstrating that depolymerization severity alone does not determine product quality. Integrated catalyst and product analyses show that Mo/H-Beta benefits from balanced acidity, dispersed redox-active MoO x species, mixed-valence Mo retention after reaction, and lower carbonaceous deposition. Overall, effective lignin valorization over supported Mo catalysts requires support-enabled acid–redox balance rather than stronger cracking alone. Graphical Support identity dictates MoO x acidity–redox balance during kraft lignin depolymerization under hydrogen-lean conditions. Integrating NH 3 -TPD, H 2 -TPR, and fresh/spent XPS with GPC and curated GC–MS shows that Mo/H-Beta couples selective C–O bond cleavage with stabilization and deoxygenation, maximizing aromatic monomer yield beyond molecular-weight reduction alone.