Single Atom-Cluster Synergy in Cu Catalysts Enhances the Transfer Hydrogenation of Ethyl Acetylpropionate to γ-Valerolactone

The non-noble metal catalysts anchored on carbon materials for the catalytic transfer hydrogenation (CTH) of biomass-derived carbonyl compounds still suffer from the problems of low activity and the necessity for co-catalyst addition. Herein, Cu single-atom catalysts (SACs) anchored on porous N-doped carbon (Cu SA+C /NC) are prepared by a high internal-phase emulsion template combined with the impregnation method, which includes the Cu-N 4 single-atom sites and Cu atom clusters with atomic-layer thickness. Significantly, the Cu SA+C /NC exhibits high activity for the catalytic transfer hydrogenation (CTH) of ethyl acetylpropionate (EL) to γ-valerolactone (GVL), obtaining a 97.3% GVL selectivity at 98.1% EL conversion under 160 °C for 6 h, which is much higher than other control catalysts and most of the previously reported catalysts. The excellent catalytic performance is attributed to the synergistic effect between Cu-N 4 single-atom sites and Cu atom clusters in Cu SA+C /NC, where Cu atom clusters act as electron-rich sites for the deprotonation of isopropanol to cleave off active H atoms, while Cu-N 4 single-atom sites are used as electron-deficient sites to accelerate the lactonization of EL. Meanwhile, the high mass transfer efficiency of NC support is beneficial for the improvement of the substrate flux and mass transfer rate, thus improving the reaction kinetics. Moreover, Cu SA+C /NC exhibits outstanding stability and broad applicability, underscoring its potential for practical application. This work develops a promising method to enhance the catalytic activity and GVL selectivity for the CTH of EL.