Influence of Cu grain size on the performance of Cu-based catalyst in the gas-phase hydrogenation of ethyl levulinate

Abstract

γ-valerolactone (GVL) is a platform chemical derived from lignocellulose, which can be used as fuel additives, green solvent and feeding for the production of other high-value chemicals. Its efficient synthesis is of great significance for the development and utilization of biomass downstream products. Herein, with CuZnAl hydrotalcite as the precursor, a series of Cu-based catalysts with different Cu grain sizes were prepared by changing the aging temperature and used in the solvent-free gas-phase hydrogenation of ethyl levulinate (EL) to produce GVL. The Cu-based catalysts were systematically characterized by various techniques such as N₂ sorption, XRD, SEM, TEM, H₂-TPR, NH₃-TPD, and in situ XPS, while the effect of Cu grain size on the performance of Cu-based catalyst in the EL hydrogenation was investigated. The results indicate that the electron cloud density of Cu as well as the Cu⁰/(Cu⁰+Cu⁺) ratio increase with a decrease of the Cu grain size; in addition, the Cu-based catalyst prepared by aging at a low temperature displays a large surface area and abundant acid sites. The synergistic effect of Cu⁰ sites and acid sites endows the Cu-based catalyst with superior performance in the EL hydrogenation to GVL. In particular, for the EL gas-phase hydrogenation under mild conditions (atmospheric pressure, 140 ℃, 0.3 h⁻¹), the Cu-based catalyst prepared by aging at 30 ℃ achieves an EL conversion of 99.9% and a selectivity of 99.5% to GVL, with no significant deactivation observed in 240 h. The insight shown in this work should be meaningful for the large-scale production of GVL.