Sonochemical synthesis of Zn-promoted porous MgO-supported lamellar Cu catalysts for selective hydrogenation of dimethyl oxalate to ethanol and their long-term stability

Abstract

The environmentally benign hydrogenation reaction of dimethyl oxalate (DMO) to produce the important platform chemicals methyl glycolate (MG), ethylene glycol (EG) and ethanol (EtOH) has gained significant importance in recent years. In this work, novel and highly efficient catalysts composed of Zn-doped lamellar Cu nanocrystals supported on porous MgO nanoparticles were synthesized using an innovative and facile sonochemical approach, and applied in the DMO hydrogenation reaction. The obtained catalytic activity revealed that the addition of Zn was found to significantly enhance the catalytic performance. The product selectivity dramatically changed from MG selectivity (88%) for the un-doped catalyst to a high EtOH selectivity of 98% for the Zn-doped Cu/MgO catalyst. To understand the relationship between the catalyst structure and the catalytic performance, the prepared, reduced and spent Cu/MgO and Zn-doped Cu/MgO catalysts were thoroughly characterized using XRD, TEM, HR-TEM, EDS mapping analysis, N₂ physical adsorption, XPS, Cu-LMM, FTIR and H₂-TPR techniques. The enhancement in the deep hydrogenation reaction for the Zn-doped catalyst to produce high EtOH selectivity is attributed to the improved dispersion, crystal defects, surface segregation and the synergistic ratio effect between Cu⁰/(Cu⁰ + Cu⁺) in the catalyst. Moreover, the produced catalysts maintained high efficiency for DMO conversion and EtOH selectivity with long-term stability for at least 200 h. The developed sonochemical approach in this study seems to be promising for the green and surfactant-free aqueous synthesis of highly efficient heterogeneous catalysts.