Highly Efficient and Recyclable Nitrogen-Doped Mesoporous Carbon-Supported Ru Catalyst for the Reductive Amination of Levulinic Acid/Esters to Pyrrolidones

Abstract

A highly effective transformation from renewable biomass and its derivatives into high-value-added chemicals and biofuels is important and challenging. Herein, a N-doped mesoporous carbon (NMC)-supported Ru catalyst developed by an incipient wetness impregnation method was reported for the reductive amination of levulinic acid (LA)/esters with amines to N-substituted 5-methyl-2-pyrrolidinones. A complete conversion of LA with a 99.8% yield of N-hexyl-5-methyl-2-pyrrolidinone (HMP) was achieved over 0.05 mol % Ru/NMC under mild conditions of 120 °C and 1.5 MPa H2 for 4 h, giving a high turnover frequency (3667 h–1). Furthermore, Ru/NMC exhibited superior stability and recyclability (reusable 21 cycles without loss of activity). The excellent performance of the Ru/NMC catalyst was mainly attributed to the introduction of N species to the mesoporous carbon, which not only improved the anchoring and the dispersion of Ru nanoparticles on the catalyst surface but also provided moderate basic sites and transferred electrons from NMC to Ru nanoparticles, as revealed by detailed characterizations. Additionally, the developed Ru/NMC catalytic system was applicable to LA/esters and various amines to afford the corresponding N-substituted 5-methyl-2-pyrrolidinones with excellent yields (80–99%).