Lanthanum Oxide-Modified Cu/SiO₂ as a High-Performance Catalyst for Chemoselective Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Abstract

Several lanthanum oxide-modified Cu/SiO2 (La-Cu/SiO2) catalysts synthesized by urea-assisted gelation and postimpregnation were used for the vapor-phase chemoselective hydrogenation of dimethyl oxalate (DMO) into ethylene glycol (EG). The 1.0La-Cu/SiO2-u catalyst with 1.0 wt % La loading was found to have the highest activity, whereas the catalyst with higher La loading at 3.0 wt % adversely affected the deterioration of catalytic activity. H2-TPR results revealed that strong interactions between La promoters and Cu species substantially changed catalyst reducibility and made some Cu2+ species on catalyst precursors difficult to be reduced. Several positive variations induced by the introduction of La were confirmed by in situ XRD, N2O chemisorption, H2-TPD, X-ray Auger electron spectroscopy, and in situ FT-IR of chemisorbed CO. These variations included increased Cu metallic dispersion, improved ability for H2 activation, elevated surface concentration of Cu+ species, and enhanced stability of catalyst nanostructure. The formation of unique Cu–O–La bonds between LaOx and cupreous species located at interfacial sites was presumably responsible for the improved catalytic performance and stability of La-Cu/SiO2-u catalyst.