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 γ-valerolactone (GVL) production from ethyl levulinate (EL) utilizing non-noble metal catalysts within a supercritical isopropanol (IPA) system. Nickel-loaded nickel–aluminum oxide nanosheets (NiXAl-R) were fabricated via hydrothermal treatment of Ni–Al layered double hydroxide precursors, followed by hydrogen reduction at 550 °C for 1.5h. Using NiXAl-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 molGVL g−1 h−1 reaction efficiency after 1.5h in supercritical IPA. The catalytic activity of NiXAl-R remained stable over five catalytic cycles. The surface of NiXAl-R exhibits abundant oxygen vacancies and unsaturated Al species (Alx+), 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 Alx+-catalyzed intramolecular esterification of 4-HPE into GVL.