The synthesis of high-efficiency and low-cost catalysts for hydrodeoxygenation (HDO) of waste lignin into advanced biofuels is crucial for enhancing current biorefinery processes. The choice of catalysts for these processes is restricted to high stability in aqueous phase as well as the best compromise between performance and price. In this study, Super Lewis acids containing the triflate anion [e.g., Hf(OTf)₄, Ln(OTf)₃, In(OTf)₃ Al(OTf)₃] and noble metal catalysts (e.g., Ru/C, Ru/Al₂O₃) formed efficient catalytic systems to generate saturated hydrocarbons from lignin in high yields. In such catalytic systems, the metal triflates mediated rapid ether bond cleavage through selective bonding to etheric oxygens while the noble metal catalyzed subsequent hydrodeoxygenation (HDO) reactions. Super Lewis acids plausibly interact with lignin substrates by protonating hydroxyl groups and ether linkages, forming intermediate species that enhance hydrogenation catalysis by supported noble metal catalysts. Meanwhile, the hydrogenation of aromatic rings by the noble metal catalysts can promote deoxygenation reactions catalyzed by super Lewis acids. In addition, the combination of a 3d transition metal (Fe, Ni, Cu, Zn) with Ru can modulate the hydrogenolysis activity of Ru and help prevent the hydrocarbon products from forming gaseous products through over-hydrogenolysis. Among these catalysts, Ru-Cu/HY showed the best HDO performance, giving the highest selectivity to hydrocarbon products due to (1) high number of strong acid sites, (2) good dispersion of metal species and limited segregation, (3) high adsorption capacity for polar fractions, including hydroxyl groups and ether bonds.

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