CuCoCe Catalysts Supported On Carbon Nanotubes For Higher Alcohol Synthesis From Syngas

Syngas（H₂+CO） is one of the most important raw material and intermediate product in chemical industry. Higher alcohol not only can be used as alternative fuels and clean gasoline additives, also can be used as chemicals and chemical raw materials. In recent years, the value of higher alcohols in the field of energy, chemical industry and environmental protection increased prominently, and related research has become actively. Synthesis of higher alcohol from syngas is one of the important ways for clean utilization of coal resources. In the current development of higher alcohol catalyst system, Cu Co based catalysts for its mild reaction condition, high activity and high selectivity of C2+OH is considered to be one of the catalysts with most industrial application prospect.A series of Cu Co Ce catalysts were prepared by co-impregnation method in this study to investigate the property of catalysts. Firstly, we compared the effect of catalyst preparation methods and reaction conditions（Pressure and temperature） and optimized the process of catalyst preparation and reaction process according the experiment results. On this basis we adjusted the mass ratio of Cu/Co active metals and explored the influence of this change. On the other hands, we also studied the effect of the length and carboxy group of carbon nanotube channels on Cu Co Ce catalysts. The catalysts were characterized by X-ray diffraction（XRD）, N₂-adsorption-desorption isotherms（BET）, temperature-programmed reduction of hydrogen（H₂-TPR）, transmission electron microscopy（TEM）, and X-ray photoelectron spectroscopy（XPS）. The main conclusions were as follows:（1） Ultrasound-assisted incipient-wetness impregnation method can promote the dispersion of active metals on catalyst surface, and decrease the reduction temperature of catalyst obviously. This is a more appropriate method of catalyst preparation for our study.（2） Increasing reaction pressure is beneficial to the catalytic activity. However, when the reaction pressure exceed 4.0 MPa, the selectivity of methanol increased significantly in alcohol distribution. We finally choosed 3.0 MPa as reaction pressure considered the products yield and selectivity of higher alcohol. The catalytic activity of catalysts is very low when reaction temperature is less than 300 ℃. However, there will be lot of hydrocarbon when the temperature exceed 340 ℃. The most suitable reaction temperature is 320³30 ℃.（3） Proper Cu/Co ratio can make catalysts had better crystal structure, higher dispersion of metals and decrease reduction temperature obviously. The catalyst had highest catalytic activity and selectivity of higher alcohols when the mass ratio of Cu/Co is 2.（4） The carboxyl group on carbon nanotubes could enhance the interaction between active metal and support, and make Cu2+ hard to be restored, which reduced the formation of methanol and remarkbly enhanced the selectivity of C2+OH.（5） Both carboxyl groups and shorter carbon nanotubes are beneficial to the impregnation of metal components, which can significantly improve the activity of catalysts. The catalyst supported on carbon nanotubes of 0.5-2 μm with 2.0 wt% carboxyl group had highest space-time yield（783.72 mg·gcat-1·h-1） and the selectivity of C2+OH reached 75.95 wt%.