Rhenium-promoter-free ruthenium–zirconia catalyst for high-yield direct conversion of succinic acid to 1,4-butanediol in water

The direct conversion of succinic acid to 1,4-butanediol (1,4-BDO) in water was investigated using Ru deposited on oxygen-vacant zirconia (Ru–O_vZrO_x) as the catalyst. 1,4-BDO was produced in high yield (89.5 %) and space–time yield (0.19 h⁻¹) at 200 °C. The proximity of Ru to O_vZrO_x stabilized the nanosized Ru⁰ particles, enabled hydrogen spillover, increased the acidity of the catalyst, and achieved intermediate adsorption. The Zr^δ+ center (2 ≤ δ < 4)—which featured abundant Lewis acid sites and was adjacent to the O_v sites—activated the γ-butyrolactone ring-opening reaction via a route involving 2-hydroxytetrahydrofuran formation. The electron-rich Ru⁰ center facilitated heterolytic hydrogen dissociation, and the dissociated H^– and H⁺ ions traveled to the Zr^δ+ sites and water molecules via hydrogen-shuttling mechanism. Moreover, the weakly bonded hydrogen actively participated in the hydrodeoxygenation and hydrogenation of intermediates to 1,4-BDO.