Continuous hydrocyclization of aqueous levulinic acid to γ-valerolactone over bi-functional Ru/NbOPO4/SBA-15 catalyst under mild conditions

Herein, we demonstrate that surface acid-base properties have marked effect upon the performance (activity, selectivity and stability) of supported Ru catalysts upon tandem hydrocyclization (hydrogenation-dehydration) of aqueous levulinic acid. A mesoporous bi-functional Ru/NbOPO4/SBA-15 catalyst incorporating highly dispersed Ru sites and well balanced strong Brønsted acidic sites (optimum B/L and M+S/W ratio) was identified, which outperformed the benchmark monofuncational (Ru/SBA-15, Ru/MCM-41) and physically blended bi-functional catalysts (Ru catalysts mixed with acid co-catalysts e.g. NbOPO4/Amberlyst-15). Further, the catalyst also demonstrated remarkable stability in a fixed-bed reactor, maintaining steady activity and γ-valerolactone selectivity (72–86%) during ca. 300 h time on stream (10 bar, 90–100 °C), corroborating its industrial potential. The exceptional performance and durability of the bi-functional catalyst was attributed to the presence of well dispersed hydrothermally and chemically stable acid (NbOPO4) and redox (Ru) sites.