Systematic study on efficient transfer hydrogenation of levulinate esters to γ-valerolactone over robust catalyst

Abstract

The CuMgZrO_x oxide catalysts were employed with economical 2-PrOH as the hydrogen donor for catalytic transfer hydrogenation of ethyl levulinate (EL) to γ-valerolactone (GVL). The cost-effective Cu₁Mg_1.15Zr₂O_x catalyst exhibited excellent physicochemical properties, with 99.8 % EL conversion and 88.0 % GVL yield. Studies have shown that sufficient basic sites of the catalyst, along with the maintenance of the Cu²⁺/Cu⁺ state rather than Cu⁰, are crucial for achieving high GVL yields. Optimization of the substrate-to-hydrogen donor ratio (1:3), along with recycling tests and characterization, demonstrated excellent activity (99.5 % EL conversion and 90.0 % GVL yield) and cycle stability for the Cu₁Mg_1.15Zr₂O_x catalyst, highlighting its strong potential for practical applications. The mechanism for GVL production from EL via the metal hydride as the dominant route was proposed based on rigorous experimental studies and in-depth characterization. Substrate scope evaluation showed that the Cu₁Mg_1.15Zr₂O_x catalyst also exhibited outstanding activity in converting methyl levulinate and butyl levulinate to GVL.