CoNi Alloy Nanoparticles Confined in N-Doped Porous Carbon as an Efficient and Versatile Catalyst for Reductive Amination of Levulinic Acid/Esters to <i>N</i>-Substituted Pyrrolidones

Abstract

Highly efficient transformation of renewable biomass and its derivatives into high-value-added chemicals and biofuels over non-noble-metal catalysts is attractive but challenging. Herein, we developed non-noble CoNi alloy nanoparticles confined in N-doped porous carbon (CoNi@NC) via simple pyrolysis of the metal–organic framework (MOF) precursor at 900 °C under an inert atmosphere. The as-obtained CoNi@NC catalyst exhibited higher performance than monometallic Co@NC and Ni@NC catalysts in the reductive amination of levulinic acid (LA) with benzylamine to N-benzyl-5-methyl-2-pyrrolidinone (BMP) under mild conditions of 130 °C and 3 MPa H2 for 6 h, achieving a full conversion of LA and a ≥ 99% yield of BMP. Detailed characterizations substantiated that multifunctional support and the significant synergistic effect between Co and Ni markedly enhanced the catalytic performance. Furthermore, CoNi@NC manifested outstanding recyclability (reusable 20 cycles without loss of activity), which was attributed to the well-dispersed CoNi alloy nanoparticles confined in the N-doped porous carbon and the anchoring of N species to metal nanoparticles. Additionally, the resultant CoNi@NC catalyst can be successfully applied in the one-pot transformation of LA/esters with amines/nitroarenes/nitriles to the corresponding N-substituted pyrrolidones, as well as the reductive amination of other carbonyl compounds with benzylamine to form N-heterocyclic compounds. Moreover, CoNi@NC enabled us to catalyze the continuous reductive amination of LA with amines in a trickle-bed reactor, which is a more promising, efficient, highly atomically economic, and green synthetic methodology, and exhibited excellent stability during the reaction over 36 h.