Efficient synthesis of γ-valerolactone from ethyl levulinate via catalytic transfer hydrogenation in supercritical isopropanol over nickel aluminum oxide nanosheets

This study reports a novel method for gamma-valerolactone (GVL) production from ethyl levulinate (EL) utilizing nonnoble metal catalysts within a supercritical isopropanol (IPA) system. Nickel -loaded nickel -aluminum oxide nanosheets (Ni X Al-R) were fabricated via hydrothermal treatment of Ni -Al layered double hydroxide precursors, followed by hydrogen reduction at 550 degrees C for 1.5 h. Using Ni X Al-R as the catalyst and IPA as the hydrogen donor, we achieved notable results: 82.7% EL conversion, 73.6% GVL yield, and 1.178 mol GVL g - 1 h -1 reaction efficiency after 1.5 h in supercritical IPA. The catalytic activity of Ni X Al-R remained stable over five catalytic cycles. The surface of Ni X Al-R exhibits abundant oxygen vacancies and unsaturated Al species (Al x+ ), which promote the initial transfer hydrogenation of EL to form the ethyl 4-hydroxypentanoate (4-HPE) intermediate. Simultaneously, the supercritical IPA environment overcomes mass transfer limitations at the solid -liquid interface between 4-HPE and the catalyst, thereby facilitating the Al x+ -catalyzed intramolecular esterification of 4-HPE into GVL.