Catalytic transfer hydrogenation of levulinic acid to gamma-valerolactone over a zirconium-based FDCA hybrid: insights into the effect of heteropoly acids

Abstract

It is incredibly challenging to design a catalyst with high activity for catalytic transfer hydrogenation (CTH) of levulinic acid (LvA) into gamma-valerolactone (GVL). In our previous work, we have designed a mesoporous acid-base bifunctional hybrid (Zr-FDCA) with high contents of Lewis acid (LA) and Lewis base (LB) sites from zirconium and 2,5-furandicarboxylic acid (FDCA) by using acetic acid as the modulator, which exhibited an outstanding performance in CTH of furfural into furfuryl alcohol. However, the catalytic performance was not satisfactory in CTH of LvA into GVL. Herein, we modified a Zr-FDCA hybrid with the introduction of phosphotungstic acid (HPWO). Comprehensive characterization revealed that HPWO could significantly affect the acidity, which afforded acid catalytic activity and introduced a Brønsted acid (BA) site. The synergistic effect between LA and BA sites resulted in the outstanding catalytic activity in CTH of LvA into GVL; a GVL yield of 95.4% with a high formation rate of GVL (12.72 mmol g⁻¹ h⁻¹) was obtained over Zr-FDCA-HPWO. Simultaneously, it also showed an ideal cycle stability and could be used for at least five consecutive runs with no significant loss in the catalytic activity.