447637 Controllable Synthesis of Highly Dispersed Cu/SiO2 Catalysts in Supercritical CO2 and Their Application in the Hydrogenation of Dimethyl Oxalate to Ethylene Glycol
Controllable Synthesis of Highly Dispersed Cu/SiO2 Catalysts in Supercritical CO2 and their Application in the Hydrogenation of Dimethyl Oxalate to Ethylene Glycol
Qin-Qin Xu, Guo-Yue Qiao and Jian-Zhong Yin*
State Key Laboratory of Fine Chemicals, School of Chemical Machinery, Dalian University of Technology, Dalian 116024, China,
Ethylene glycol (EG) is widely used as antifreeze and precursors in the production of polyesters. One of the most promising approach to EG is coal-based production technology via dimethyl oxalate (DMO) hydrogenation. Preparation of highly active catalysts plays a key role in the synthesis of EG through the coal chemical industry. There are some disadvantages for the traditional methods to prepare these copper-based catalysts, for example, the active components are usually poorly dispersed for the impregnation method and the metal loading is quite low for the ion exchange method. Ammonia-evaporation method is characterized by highly dispersed active components with high metal loading, however, ammonia is very toxic.
In this study, highly dispersed and morphology controllable Cu nanostructures were synthesized within mesoporous silica in supercritical CO2 using organic or inorganic Cu precursors. Deposition pressure, temperature, time and the mass ratio of the precursor to substrates were found to influence the size of the nanostructures and the metal loading. Furthermore, Co-solvent was found to have significant influence on the morphology of the nanostructure. Although the inorganic precursor has large solubility in ethanol, methanol and n-butyl alcohol, only big nanoparticles outside the nanochannels were obtained when these three co-solvents were used. However, when ethylene glycol or the mixture of ethylene glycol and water were used as co-solvents, large amounts of short nanotubes were found inside the nanochannels with large metal loading. It indicates that the role of the co-solvent may have many aspects, such as enhancement of the precursor dissolution, change of the interaction between the precursor and the substrates and so on. Finally, the activity, selectivity and stability of Cu/SiO2 catalysts for the hydrogenation of dimethyl DMO to EG were evaluated.
Fig.1 TEM images of Cu/SBA-15 prepared in supercritical CO2
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