Efficient conversion of various biomass-derived feedstocks into γ-valerolactone over a composite Au NP/KIT-6 catalyst using formic acid as the hydrogen carrier

• Mesoporous Au/KIT-6 catalyst efficiently converts LA, EL, and BL to γ-valerolactone • Formic acid is used as an effective hydrogen source for GVL synthesis • The reaction proceeds via 4-hydroxypentanoic acid as an intermediate, followed by intramolecular esterification • Optimized conditions yield 83% GVL at 230°C in 120 min • Isopropanol and H₂ experimented as alternative hydrogen donors • Catalyst retains activity over at least two reuse cycles In this study, an Au NP/KIT-6 composite catalyst comprising gold nanoparticles supported on a mesoporous KIT-6 silica framework was synthesized and applied as an efficient catalyst for selective hydrogenation of levulinic acid (LA), ethyl levulinate (EL), and butyl levulinate (BL) to γ-valerolactone (GVL), using formic acid (FA) as the hydrogen source. The hydrogenation pathway proceeds via formation of 4-hydroxypentanoic acid as an intermediate, which undergoes intramolecular esterification to yield GVL. The catalyst was thoroughly characterized using various techniques, including TEM, SEM, XPS, XRD, and N₂ adsorption-desorption analysis. The effects of several reaction parameters including temperature, reaction time, catalyst loading, and substrate-to-FA ratio were systematically investigated. Under optimized conditions (10 mg Au NP/KIT-6 catalyst, LA:FA ratio of 1:4, and reaction temperature of 230 °C), maximum GVL yield of 83% was achieved within 120 min. Comparative experiments using isopropanol (IPA) and molecular hydrogen as alternative hydrogen donors confirmed that formic acid exhibits superior activity, attributable to its dual function as both hydrogen carrier and acid promoter. Additionally, the Au NP/KIT-6 catalyst demonstrated excellent recyclability, maintaining most of its catalytic performance after two consecutive cycles. These results highlight the potential of this catalytic system for sustainable and industrially viable GVL production from biomass-derived feedstocks.