Solvent-Modulated Multiple Active Hydrogen Species in Furfural Hydrogenation

Unveiling the mechanism behind catalyst-dependent solvent effects for hydrogenation reactions is critically important yet presents significant challenges. In this work, focusing on furfural hydrogenation over Pd-based catalysts, we observe that distinct active hydrogen species present on Pd/MgO and Pd/TiO2 exhibit different responses to solvation environments, consequently influencing the selectivity in diverse solvents. Product distribution over Pd/MgO remains unaffected by the solvents used that tetrahydrofurfural (THFAL) emerged as the primary product in both organic solvents and water. Conversely, product distribution over Pd/TiO2 highly depends on the solvents; THFAL dominates in organic solvents, whereas furfural alcohol (FOL) becomes the primary product in water. The disparate selectivity upon alteration of supports and solvents is demonstrated by neural network-enhanced molecular dynamics simulations and microkinetic modeling. The active hydrogen species on the support are stabilized in water by water-mediated charge reconstructions, facilitating the hydrogenation of C═O to produce FOL. A spillover pathway where hydrogen species transfer to supports directly without involving hydrogen bond networks is dynamically preferred in both water and organic solvents.