Importance of the Initial Oxidation State of Copper for the Catalytic Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Exposing a Cu-based catalyst to a suitable temperature is of great importance to optimize its hydrogenation performance, as copper is sensitive to temperature. Herein, we investigated the effect of the initial oxidation state of copper, tuned by the reduction temperature, on its catalytic performance in the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) through designing a series of catalysts with different reduction temperatures (200-350 °C). Among these catalysts, the Cu/SiO₂ catalyst prepared by ammonia evaporation with a hydrogen reduction process at 250 °C showed the best performance in the hydrogenation of DMO with a conversion of 100 % and a selectivity to EG higher than 95 %. The relationship between the initial oxidation state of copper and catalytic performance was well established by characterizing the physicochemical properties of the Cu/SiO₂ catalysts by XRD, TEM, H₂ temperature-programmed reduction, N₂O adsorption, and in situ reduction Auger electron spectroscopy. The initial oxidation state of copper determined the conversion of DMO and the distribution of the products, and it could be balanced by reducing the temperature to improve the activity of the catalyst. This work provides a reference for further exploration of the mechanism and guidance for the design of catalysts for the hydrogenation of esters.