Hydrodeoxygenation of Furylmethane Oxygenates to Jet and Diesel Range Fuels: Probing the Reaction Network with Supported Palladium Catalyst and Hafnium Triflate Promoter

Catalytic hydrodeoxygenation of furylmethane oxygenates to high carbon branched chain jet and diesel fuel range alkanes under mild reaction conditions is a promising strategy for energy-efficient production of fuels with minimal C–C cracking to undesired products. Here, we report that a strong Lewis acidic promoter can overcome the energy barrier for furylmethane hydrodeoxygenation at lower temperature. Furan rings of furylmethanes are first hydrogenated to fully saturated cyclic ethers by a hydrogenation catalyst, which then undergo facile ring opening and deoxygenation by the promoter. A cyclic intermediate between ethereal O and the Lewis acidic metal center, assisted by the triflate ligand of the promoter, is formed in the ring-opening step. Probing the reaction pathway with symmetric single furan ring surrogate molecules suggests that the promoter is necessary for the ring opening. Deoxygenation of ring-opened oxygenates takes place more quickly for single furan ring surrogates than for the multiple furan ring furylmethanes. A maximum 97% jet fuel range alkanes with 93% selectivity in C15H32 and C14H30 is achieved from C15-furylmethane under optimal conditions. The yield and selectivity of alkanes with desired carbon numbers can be tuned using furylmethanes with tailored carbon chains, furan numbers, and a carbon center that minimizes C–C cracking.