Multisite CuNi/Al2O3 Catalyst Enabling High-Efficiency Reductive Amination of Biomass-Derived Levulinic Acid (Esters) to Pyrrolidones under Mild Conditions

The reductive amination of biomass-derived levulinic acid (LA) and its esters to pyrrolidones over non-noble metal catalysts under mild conditions represents a promising but challenging strategy for valorizing biomass resources into nitrogen-functionalized chemicals. Herein, we report the fabrication of Al2O3-supported bimetallic CuNi composite catalysts by a simple coprecipitation–calcination–reduction method for high-efficiency reductive amination of LA (esters) into pyrrolidones in ethanol under mild reaction conditions (80 °C, 10 bar H2, and 6–24 h). We show that the multisite division on the as-prepared Cu1Ni1/Al2O3-H2 catalyst with a Cu/Ni molar ratio of 1:1 enables a distinguished catalytic activity toward the formation of pyrrolidones via an amine-intermediate mechanism. A deliberate structure–activity correlation reveals that the abundant and well-dispersed mesopores, oxygen vacancies, strong Lewis acid sites, and Cu/Ni NPs on the composite catalyst synergistically contribute to the high-efficiency conversion of LA (esters) to pyrrolidones, wherein the oxygen vacancies are responsible for the adsorption/activation of ethyl levulinate (EL), the Lewis acidic coordination-unsaturated Ni species are responsible for the adsorption/activation of butylamine, the Cu/Ni NPs are in charge of the adsorption/dissociation of H2, and the mesopores provide adequate space for tolerating substrates with higher steric hindrance. Moreover, a remarkable electron transfer from adjacent Ni species to Cu centers occurs, which is conducive to improving the inherent catalytic activity of the non-noble bimetallic composite catalyst by enhancing the electron density of Cu NPs and the Lewis acidic strength. Remarkably, the catalytic system exhibits great performance for converting a variety of biomass-derived LA (esters) with extensive nitrogen sources (e.g., NH3, aliphatic/aromatic primary amines, nitriles, and nitro compounds), thereby representing an advance toward the valorization of biomass-derived initial platform chemicals into N-containing fine chemicals. It may provide a valuable reference for the rational construction of advanced non-noble metal catalysts in a future biorefinery.