Abstract: A series of Cu/SiO₂ catalysts for the hydrogenation of dimethyl oxalate to ethylene glycol were prepared by the sol-gel method. Under optimized hydrogenation conditions, dimethyl oxalate conversion and ethylene glycol selectivity were found to reach 99.9% and 95.0%, respectively, upon varying the copper loading between 15% and 25%. The prepared catalysts were characterized by N₂-physisorption, transmission electron microscopy, X-ray diffraction, H₂-temperature-programmed reduction, N₂O titration, and X-ray photoelectron spectroscopy. The results show that when the copper loading was increased under the same experimental conditions the factors that mostly affect the activities of the catalysts prepared by the sol-gel method are encapsulation and agglomeration. The encapsulation of silica is strong and it becomes the major factor when w(Cu) ≤ 10% while agglomeration among the copper species on the catalyst surface becomes more serious and is a major factor when w(Cu) > 10%. These two factors influence the surface structure, the morphology of the copper species, and the chemicals surroundings the catalysts and as a result the performance of the catalysts is affected too.

Key words: sol-gel method, dimethyl oxalate, hydrogenation, copper, silica, ethylene glycol, encapsulation, agglomeration