A Promising Strategy for Solvent-Regulated Selective Hydrogenation of 5-Hydroxymethylfurfural over Porous Carbon-Supported Ni-ZnO Nanoparticles

Developing biomass platform compounds into high value-added chemicals is a key step in renewable resource utilization. Herein, we report porous carbon-supported Ni-ZnO nanoparticles catalyst (Ni-ZnO/AC) synthesized via low-temperature coprecipitation, exhibiting excellent performance for the selective hydrogenation of 5-hydroxymethylfurfural (HMF). A linear correlation is first observed between solvent polarity (ET(30)) and product selectivity within both polar aprotic and protic solvent classes, suggesting that solvent properties play a vital role in directing reaction pathways. Among these, 1,4-dioxane (aprotic) favors the formation of 2,5-bis(hydroxymethyl)furan (BHMF) with 97.5% selectivity, while isopropanol (iPrOH, protic) promotes 2,5-dimethylfuran production with up to 99.5% selectivity. Mechanistic investigations further reveal that beyond polarity, proton-donating ability is critical in facilitating hydrodeoxygenation. iPrOH enables a hydrogen shuttle mechanism where protons assist in hydroxyl group removal, lowering the activation barrier. In contrast, 1,4-dioxane, lacking hydrogen bond donors, stabilizes BHMF and hinders further conversion. Density functional theory calculations confirm a lower activation energy in iPrOH (0.60 eV) compared to 1,4-dioxane (1.07 eV). This work offers mechanistic insights and a practical strategy for solvent-mediated control of product selectivity in biomass hydrogenation, highlighting the decisive role of solvent-catalyst-substrate interactions.