Protonation prerequisite in selective furfural hydrogenation to furfuryl alcohol: a kinetic isotope effect study

The electrochemical hydrogenation of furfural (FF) to furfuryl alcohol (FA) offers a sustainable route for biomass valorization, yet selectivity remains challenged by uncontrollable radical-mediated polymerization. Herein, we demonstrate that enforcing a protonation-first pathway through tailored interfacial kinetics effectively suppresses undesired C–C coupling at electrified interfaces. By engineering a PdCu bimetallic oxide catalyst with synergistic dual-active sites—electron-deficient Cu ^δ+ delaying premature electron transfer and oxophilic Pd-O-Cu clusters enhancing water dissociation—we prioritize protonation of the carbonyl group prior to electron transfer. This spatiotemporal decoupling is validated by a secondary inverse kinetic isotope effect (KIE = 0.66 ± 0.06), eradicating polymerization channels and achieving near-unity (99.9%) FA selectivity on the optimized catalyst, fourfold higher than conventional Cu catalyst. This work establishes a universal framework for controlling proton-coupled electron transfer sequences in biomass electroreduction, offering a blueprint to mitigate polymerization in reactions involving electrophilic carbonyl intermediates.