Mechanistic Insights into the Solvent-Driven Adsorptive Hydrodeoxygenation of Biomass Derived Levulinate Acid/Ester to 2-Methyltetrahydrofuran over Bimetallic Cu–Ni Catalysts

A highly efficient bimetallic Cu–Ni catalytic system for selective hydrogenation of levulinic acid/ester to 2-methyltetrahydrofuran (2-MTHF) promoted by the solvent was presented. A 98% yield of 2-MTHF was achieved with optimal 10Cu-5Ni/Al2O3 catalyst at a mild temperature in the presence of nonpolar organic solvent n-hexane and molecular hydrogen. A mechanistic study revealed a synergistic effect between Cu and Ni nanoparticles, wherein Ni primarily activated H2 and hydrogenated levulinic acid/ester to GVL and Cu facilitated the hydrogenation of GVL to 2-MTHF. Detailed studies on solvent effects revealed that the n-hexane possessed higher H2 dissolvability and enhanced adsorption of GVL on the catalyst surface to facilitate its conversion to 2-MTHF, providing a lower apparent activation energy barrier of 48.9 kJ/mol for the rate-determining step. DFT calculations also indicated a highest adsorption energy of GVL with Al2O3 over other substrates and solvent molecules, further highlighting the promotion effect of nonpolar n-hexane solvent.