A Highly Dispersed and Stable Cu–Fe Nanocatalysts for Ethyl Levulinate Hydrogenation

Abstract

Cu-based nanocatalysts have potential applications in the selective hydrogenation of biomass-derived platform molecules. Currently, a main challenge is the poor stability of Cu catalysts under harsh reaction conditions due to metallic Cu sintering and agglomeration. Herein, a series of Cu_xFe_y/Al₂O₃ nanocomposite catalysts was prepared via controlled solution combustion synthesis (SCS) owing to its minimal reaction time and energy requirements that reduce Cu agglomeration. Among them, the Cu₅Fe₃/Al₂O₃ catalyst exhibited the most favorable structure with the smallest grain size of 2.09 nm, highest dispersion of 63.6%, and an optimal Cu⁺/Cu⁰ ratio of 1.0 than the traditional Cu/Al₂O₃ counterpart. The synergy between Fe₂O₃ and Cu inhibited the thorough reduction of Cu²⁺ to Cu⁰ and consequently facilitated H₂ dissociation and activation as well as the highly efficient activation of the ethyl levulinate’s (EL) carbonyl group. Unlike the traditional Cu/Al₂O₃ catalyst, for which activity rapidly decreased from 97% to 11% over 200 h, the Cu₅Fe₃/Al₂O₃ catalyst exhibited a high GVL yield of 85% and maintained excellent stability, attributable to the strong interaction between Cu nanoparticles and Al₂O₃ support as well as the confinement effect with barrier property of Fe doping. Therefore, the inexpensive, efficient, and stable Cu₅Fe₃/Al₂O₃ catalyst has potential applications in the selective hydrogenation of biomass-derived platform compounds.

Solution combustion synthesis was employed to prepare a Cu–Fe/Al₂O₃ nanocomposite catalyst, which exhibited excellent catalytic performance in the hydrogenation of biomass-derived ethyl levulinate to γ-valerolactone (GVL). This catalyst surpassed the performance of the traditional Cu/Al₂O₃ catalyst, particularly in terms of demonstrating a high GVL yield of 85% and maintaining stability for over 200 h. This excellent performance could be attributed to its high Cu dispersion, small grain size, and optimal Cu⁺/Cu⁰ ratio.

Graphical Abstract