Conversion of biomass-derived ethyl levulinate into gamma-valerolactone via hydrogen transfer from supercritical ethanol over a ZrO2 catalyst

A green and efficient process was developed for the conversion of biomass-derived ethyl levulinate (EL) into gamma-valerolactone (GVL) using supercritical ethanol as the hydrogen donor and the reaction medium over low-cost and eco-friendly ZrO2 catalysts, which were prepared by the precipitation method and characterized by BET, SEM, XRD, FT-IR, TGA-DTA, TPD-NH3 and TPD-CO2. The results indicated that amorphous ZrO2 with a high specific surface area and a large number of acid-base sites exhibited the highest catalytic activity, an excellent GVL yield of 81.5% with 95.5% EL conversion was achieved at 523 K over 3 h. In addition, combined with the results of poisoning experiments, a plausible mechanism of catalytic transfer hydrogenation (CTH) via a six-membered ring transition state was also presented.