Sonochemical engineering of highly efficient and robust Au nanoparticles wrapped on Fe/ZrO2 nanorods and their controllable products selectivity in dimethyl oxalate hydrogenation
Considerable interest has been paid in last few years for the environmentally-benign hydrogenation reaction of dimethyl oxalate (DMO) to produce methyl glycolate (MG), ethylene glycol (EG) and ethanol (EtOH). Cu-based composite and noble-metals promoted Cu-materials have been reported as highly efficient catalysts in DMO hydrogenation. In this study, for the first time, Cu-free Fe/ZrO2 nanorods catalyst with high crystalline structure was synthesized in absence of any toxic-related materials and through one-pot sonochemical approach and used without the calcination step as robust catalyst in DMO hydrogenation to produce high EtOH yield of 94.4%. Furthermore, to control the products distribution in this multistep DMO hydrogenation and achieve high MG selectivity of 95%, highly dispersed Au nanoparticles were nicely decorated on the surface of Fe/ZrO2 nanorods catalyst by facile sonochemical route and appointed as highly efficient catalyst. Moreover, the produced catalysts displayed high stability properties for a period of at least 300 h within maintained high catalytic activity. Interestingly, X-ray diffraction results for the spent catalysts demonstrated that the Hagg iron carbide (Fe5C2) is the active phase for the production of ethanol using Fe/ZrO2 catalyst, while, the XPS results exhibited that the co-existence of the three oxidation states of metallic Au+, Au0, and Au3+ plays the key-role as the active species for the synthesis of high MG selectivity using Au/Fe/ZrO2 catalyst.