Cu/SiO2 hybrid catalysts containing HZSM-5 with enhanced activity and stability for selective hydrogenation of dimethyl oxalate to ethylene glycol

A novel type of hybrid catalysts composed of Cu/SiO2 and H-form ZSM-5 (HZSM-5) zeolite, prepared using urea-assisted gelation method, displayed excellent catalytic activity and stability for the selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). The content and SiO2/Al2O3 ratio of HZSM-5 significantly influenced the performance of hybrid catalysts. An unprecedentedly high EG space time yield of 1.50 g g-cat−1 h−1, with DMO conversion of 99.5% and EG selectivity of 94.8%, were obtained on a hybrid catalyst containing 3 wt% of HZSM-5 with SiO2/Al2O3 = 38. The characterizations of N2 physisorption and N2O chemisorptions revealed that both specific surface area and copper dispersion were promoted by introducing HZSM-5 zeolite into the Cu/SiO2 catalyst. Moreover, X-ray Auger electron spectroscopy and in situ Fourier transform infrared spectroscopy of chemisorbed CO demonstrated that the surface Cu+ site concentration of the catalysts containing HZSM-5 was higher than those without HZSM-5. The results indicated that the introduction of HZSM-5 zeolite changed the crystallization behaviors of cupric phyllosilicate precursor, essentially improving copper dispersion and enhancing copper–silica interaction. Furthermore, the specific zeolitic cages and negatively charged framework of HZSM-5 zeolite incorporated into Cu/SiO2 entities might also be beneficial for accommodation and stabilization of highly dispersed cuprous species, which act as efficient active sites for the activation of ester groups.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (194 K)Download as PowerPoint slideHighlights► A novel type of hybrid catalyst composed of Cu/SiO2 and HZSM-5 zeolite is prepared. ► Introduction of HZSM-5 modifies the copper dispersion and surface Cu+ site concentration. ► Introduction of HZSM-5 considerably improves the heat-resistance of the catalyst. ► The hybrid catalyst shows enhanced performance for hydrogenation of dimethyl oxalate. ► The hybrid catalyst can retain its excellent activity for longer than 300 h.