Ru/TiO2 catalysts for selective formation of ring hydrogenation or ring-opening products from biomass-derived 5-hydroxymethylfurfural

Abstract

We report for the first time a one-pot catalytic route for the selective hydrogenation of biomass-derived 5-hydroxymethylfurfural (HMF) into 1,2,5-hexanetriol and related value-added products such as 1-hydroxyhexane-2,5-dione (HHD) and 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) using a Ru/TiO₂ catalyst. In particular, the influence of the solvent composition (water–dioxane) on the reaction pathways for HMF ring opening and ring reduction products was investigated, revealing that water acts not only as a sustainable solvent but also as a reactive substrate, promoting OH-group rearrangements. Under optimized conditions, BHMTHF was obtained in >99% yield in pure 1,4-dioxane, while HHD and 1,2,5-hexanetriol were produced at 90% and 75% yields, respectively, in pure aqueous media. DFT calculations on Ru(0001) surfaces indicate that water increases the concentration of surface hydroxyl species (OH*), facilitating selective ring-opening reactions. Catalyst characterization showed minor increases in Ru particle size and solvent-dependent metallic Ru availability, influenced by carbon deposition. Nevertheless, the Ru/TiO₂ catalyst retained high activity and selectivity over several cycles in both solvents. This study demonstrates a solvent-directed, highly selective strategy for converting HMF into valuable chemicals, integrating experimental and theoretical insights to advance green catalytic processes.