Tuning Selectivity in Direct 5‐Hydroxymethylfurfural Hydrodeoxygenation to 5‐Methylfurfural or 2,5‐Bis(hydroxymethyl)furan Over Ni/TiO2 Catalysts

The platform molecule 5‐Hydroxymethylfurfural (HMF) can be derived from biomass feedstocks and catalytically hydrogenated into various high value molecules. Its conversion to 5‐methylfurfural (5‐MF), a versatile synthetic intermediate and perfuming agent is challenging as the selective hydrodeoxygenation of the C–OH group in HMF is far less favorable kinetically and thermodynamically than the hydrogenation of the C═O group, which leads to 2,5‐bis(hydroxymethyl)furan (BHMF). Herein, for the first time we demonstrate that Ni/TiO₂ catalysts can be tuned to promote the selective removal of a hydroxyl group in the presence of an aldehyde moiety, achieving a high 5‐MF yield. Among various synthesis approaches, the direct ion‐exchange incorporation of Ni into a TiO₂ network prepared via an alginate synthesis route enabled identifying key factors directing the reaction selectivity toward 5‐MF. The highest 5‐MF selectivity (86%) at nearly full conversion was favored by high acidity and ultra‐high dispersion of Ni atoms on the surface, while the crucial role of titania was discussed. By contrast, increasing the reduction temperature to 700 °C significantly lowered acidity and led to the formation of larger Ni particles, which favored C═O activation and in turn promoted a selectivity shift toward BHMF achieving 86% selectivity at nearly full conversion.