Influence of dopants on the structure and catalytic features of the Cu/ZnO catalyst for dimethyl oxalate hydrogenation to ethylene glycol

The Cu-M/ZnO catalysts (M = Zr⁴⁺, Al³⁺ and Mg²⁺) for dimethyl oxalate (DMO) selective hydrogenation to ethylene glycol (EG) were synthesized by the co-precipitation method. The properties of the as-synthesized catalysts were characterized by N₂-physisorption, N₂O-titration, XRD, H₂-TPR, CO₂-TPD, SEM, FT-IR and XPS. It was found that the Cu dispersion could be effectively promoted by the dopants incorporated in the Cu/ZnO catalyst. Particularly, a trace amount of Mg²⁺ and Al³⁺ dopants could significantly reinforce the chemical interaction between the Cu and ZnO phases by embedding into the ZnO lattice, while the Cu/ZrO₂ interaction could be improved with the introduction of Zr⁴⁺. For DMO gas-phase hydrogenation, the EG yield of the Cu/ZnO catalyst increased from 75.0% to 85.0% and 90.0% in the presence of Zr⁴⁺ and Al³⁺ dopants, respectively. Particularly, the EG selectivity of Cu-Mg/ZnO catalyst reached up to 95.0% with DMO completely converted for more than 100 h. The correlation between the catalytic behavior and physicochemical features of the Cu/ZnO based catalysts suggested that the surface Cu⁺ sites was vital for the catalytic behavior with adequate Cu⁰ sites. Additionally, the strengthened Cu/oxide interaction favored the outstanding stability of the Cu-Zr/ZnO and Cu-Mg/ZnO catalyst for DMO hydrogenation.