One-Pot Conversion of Lignin into Cycloalkane-Rich Sustainable Aviation Fuel Precursors: Integrated Catalytic Depolymerization and Hydrodeoxygenation over a Bimetallic Ru–Ni/AlOx Catalyst

In this study, a hydrotalcite-derived Ru/NiAlOx catalyst was examined for one-pot conversion of lignin into a cycloalkane-rich sustainable aviation fuels (SAFs) precursor. The Ru/NiAlOx catalyst accelerated the cracking of heavy oil (phenolic oligomers) through its distinctive catalytic properties, significantly enhancing the efficiency of the one-pot conversion of lignin into cycloalkanes. The Ru/NiAlOx catalyst effectively addressed this bottleneck through multiple synergistic effects: Electron transfer from Ru to Ni nanoparticles facilitated H2 activation on electron-rich Ni0 sites, while active hydrogen migration to oxygen vacancies enhanced heavy oil adsorption and depolymerization. The small Ni nanoparticle size (4.2 nm) and high surface area (197.53 m2/g) provided abundant active sites and sufficient reaction space for the efficient hydrodeoxygenation (HDO) of oxygenated intermediates. The catalyst achieved a 78.5% lignin deoxygenation degree and maintained cycloalkane yields of 31.9–36.6 C % over five recycling runs, demonstrating remarkable activity and stability. The resulting cycloalkanes exhibited favorable fuel properties comparable to conventional jet fuels, including high heating value (49.4 MJ/kg), optimal H/C ratio (2.3 mol/mol), appropriate kinematic viscosity (4.3 mm2/s@20 °C), and suitable density (0.865 g/cm3@15 °C). This work provides an effective strategy for valorizing waste lignin into SAFs components.