Selective hydrogenation of γ-valerolactone to 1,4-pentanediol over hydrotalcite-derived CuCoAl catalysts

Abstract

In this study, a series of CuCoAl catalysts with different Cu/Co molar ratios were prepared from hydrotalcite-like precursors and then adopted for γ-valerolactone (GVL) hydrogenation to 1,4-pentanediol (1,4-PeD). By tuning the Cu/Co ratio in the CuCoAl catalysts and optimizing the reaction conditions, nearly 100% yield of 1,4-PeD was finally achieved with the Cu_0.2Co_0.8Al catalyst (Cu/Co = 1: 4) at 433 K and 4 MPa H₂. The high activity of the Cu_0.2Co_0.8Al catalyst was attributed to the existence of Cu-CoO_x synergistic active sites and the abundant surface acidity. The electron transfer from Cu to Co resulted in the formation oxygen-defected CoO_x sites and surface acidic sites, which were beneficial for the adsorption of GVL and the activation of C-O/C=O bonds. The proximity between Cu particles and defective CoO_x facilitated the dissociative adsorption of H₂ on Cu⁰ and the subsequent hydrogen spillover to CoO_x sites, thereby significantly promoted the selective hydrogenation of GVL to 1,4-PeD. In addition, applications of the Cu_0.2Co_0.8Al catalyst to the ring-opening reactions of other lactones (including α-adamyllactone, γ-caprolactone, δ-pentyllactone, and ε-caprolactone) were further investigated. Eventually, high yields (> 93%) of the corresponding diols were attained, demonstrating the excellent catalytic versatility of Cu_0.2Co_0.8Al in selective hydrogenation of lactones. Overall, this work shows high potential of hydrotalcite-derived CuCoAl catalysts for selective hydrogenation of GVL to 1,4-PeD, and provides insights for the design of efficient bimetallic catalysts in lactone hydrogenolysis.