Continuous hydrogenation of aqueous levulinic acid to γ-valerolactone under mild conditions with a highly efficient multifunctional Ru/carbon catalyst

Herein, a Ru-decorated carbon material bearing unique surface chemistry (Brønsted acidic phosphate groups, Lewis basic N-groups and oxygen functional groups) is shown to exhibit exceptional activity, selectivity and stability upon direct hydrogenation of aqueous levulinic acid (LA) (0.47 M and 0.95 M) to γ-valerolactone (GVL) under mild conditions (25–95 °C and 3.5–5 bar). The multifunctional Ru/carbon catalyst outperformed the bifunctional Ru/NbOPO₄, and blended (physically mixed) catalytic systems comprising of commercial Ru/carbon (hydrogenation catalyst) and NbOPO₄/Amberlyst 15 (acid promoter/co-catalyst). The material also demonstrated remarkable stability for energy efficient GVL production in a fixed-bed reactor under continuous flow conditions, maintaining stable GVL productivity during 52-day time on stream operating at 3.5–5 bar, 80–95 °C and low H₂/LA ratio (4–17:1 mol/mol). The exceptional catalytic performance and long term stability of the multifunctional carbocatalyst was attributed to the presence of highly active Ru(0) nanoparticles stabilized on N-doped carbon framework and acidic phosphates and RuO_x/RuO₂ sites, which promote LA hydrogenation and intramolecular esterification of 4-hydroxypenatonnic (4-HPA) in tandem, affording a high GVL selectivity. The catalyst's combination of high productivity, long-term stability, and ability work under intensified setting in mid conditions highlight its potential for energy efficient GVL production at large scale.