Construction of Cu-Ce composite oxides by simultaneous ammonia evaporation method to enhance catalytic performance of Ce-Cu/SiO2 catalysts for dimethyl oxalate hydrogenation

Abstract The complicated ammonia evaporation method (AEM) involves many steps, such as mixing, evaporating ammonia, drying, and calcining procedures, etc. Thus it is necessary to know in which stage to introduce the promoter is the most beneficial to improve the performance of the Cu-based catalysts. By introducing a cerium promoter at different stages, a series of Ce-Cu-Si-T catalysts were designed for hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). The effects of the Ce3+ ions introduced at different stages on the structure and properties of the catalysts were revealed by XRD, TEM, XPS and other characterization methods. When the Ce3+ was added with Cu2+ simultaneously at the mixing stage, it was favor to form robust Cu-Ce composite oxides. The Cu-Ce composite oxides can not only provide more active sites, but also enhance the synergy between Cu0 and Cu+. Therefore, the performance of the Ce-Cu-Si-AE catalyst was significantly improved. The average conversion of DMO and the selectivity of EG were 100.0% and 95.3% for 480 h at 458 K under a high weight liquid hourly space velocity (WLHSV) of 1.2 g g -catal - 1 h - 1 , respectively. However, the cerium promoter were adsorbed or aggregated on the surface of the copper species as the Ce3+ and Cu2+ were not introduced at the same stage, resulting in covering partial active sites and thus decreasing the catalytic performance for DMO hydrogenation. Therefore, this work provides considerable reference value for designing new stable nano copper-based catalysts and establishing an effective introduction mechanism for promoters.