Cu@C/SiO2 catalyst with tunable Cu+ species by sorbitol for the selective hydrogenation of dimethyl oxalate to methyl glycolate

An efficient Cu@C/SiO₂ catalyst for the hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) was prepared by sorbitol-modified ammonia evaporation method followed by calcination in N₂. The Cu@C/SiO₂ catalyst exhibited the superior catalytic activity and stability for DMO hydrogenation compared with the Cu/SiO₂ catalyst. The optimized Cu@C/SiO₂–1/4 catalyst exhibited an MG yield of 63 % during 90 h long-term evaluation under temperature of 210 °C, pressure of 1.9 MPa, WHSV of 1.25 g_DMO·g_Cu^-1·h^-1 and H₂/DMO of 150. The characterization results indicated that Cu dispersion can be significantly enhanced by the addition of an appropriate amount of sorbitol and the surface Cu⁰ and Cu⁺ species were effectively regulated by the amount of sorbitol. The catalytic activity of Cu@C/SiO₂ was linearly dependent on specific area of Cu⁺ species under the sufficient specific area of Cu° for H₂ dissociation. In addition, the sorbitol–derived carbon species on the catalyst were also favorable for the enhanced stability owing to the suppression of Cu sintering.