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/SiO 2 (La-Cu/SiO 2 ) 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/SiO 2 - 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. H 2 -TPR results revealed that strong interactions between La promoters and Cu species substantially changed catalyst reducibility and made some Cu 2+ species on catalyst precursors difficult to be reduced. Several positive variations induced by the introduction of La were confirmed by in situ XRD, N 2 O chemisorption, H 2 -TPD, X-ray Auger electron spectroscopy, and in situ FT-IR of chemisorbed CO. These variations included increased Cu metallic dispersion, improved ability for H 2 activation, elevated surface concentration of Cu + species, and enhanced stability of catalyst nanostructure. The formation of unique Cu–O–La bonds between LaO x and cupreous species located at interfacial sites was presumably responsible for the improved catalytic performance and stability of La-Cu/SiO 2 - u catalyst.