Fabrication of nano Cu/Cu2O@C for the conversion of glycerol to lactic acid

Abstract

In this study, Cu/Cu₂O nanoparticles encapsulated within a carbon shell (Cu/Cu₂O@C) were synthesized via calcination of a Cu-based metal–organic framework (Cu-MOF) using trimesic acid as the ligand, and employed as catalysts for glycerol conversion to lactic acid. The relationship between catalytic activity and structural properties, such as crystal structure and the ratio of active sites, was systematically investigated. The results reveal that the lattice spacing of Cu⁰ is a critical factor influencing catalytic performance. A significant increase in lactic acid yield was observed when the Cu₂O to Cu ratio remained constant but lattice spacing increased, while a modest improvement in lactic acid yield was seen with increasing Cu₂O content at constant lattice spacing. The Cu/Cu₂O@C catalyst calcined at 450 °C (Cu/Cu₂O@C-450) exhibited the highest Cu₂O content (49.83 wt%) and largest Cu⁰ lattice spacing (d = 0.221 nm), achieving 100% glycerol conversion and 89.89% lactic acid yield under optimized conditions (190 °C, 6 h, air atmosphere), with over 80% lactic acid yield maintained in the eighth cycle. Density functional theory (DFT) calculations further demonstrated that Cu/Cu₂O@C-450 exhibited higher surface charge density and adsorption energy, facilitating stronger glycerol adsorption and bonding, which enhanced conversion efficiency and lactic acid yield. These findings provide mechanistic insights into the role of lattice strain and the ratio of different Cu valence states in improving catalytic performance for glycerol valorization.