Metal/H⁺ sites modulation in the decatungstate+Pd/C catalytic system for photocatalytic generation of furfuryl ethyl ether

Furfuryl ethyl ether (FEE) is considered as one of the most important candidates for biofuels due to its high-octane number. However, it is still challenging to produce FEE via the biomass-based route under mild conditions. Here, we developed a photoinduced catalytic transfer hydrogenation (CTH) process for the efficient production of FEE through the reduction etherification of furfural (FF) using Na₄W₁₀O₃₂ (NaDT), Pd/C, and ethanol as the hydrogen atom transfer (HAT) catalyst, hydrogenation catalyst, and the H donor, respectively. Notably, the introduction of brominated benzene (PhBr) as an additive significantly promoted the yield of FEE to 92.7%. A series of experiments and characterization results indicated that the attachment and detachment of Br atoms on Pd/C catalyst surface effectively regulate the balance between H⁺ sites and Pd sites in the NaDT+Pd/C catalytic system. The balance facilitates the preferential acetalization of FF catalyzed by H⁺ sites, followed by hydrogenation to efficiently produce FEE catalyzed by Pd sites. This photoinduced CTH process exhibits good stability and recyclability as well as universality for the transformation of various organic substrates under mild conditions.