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.