Study on Amorphous Copper-Based Catalysts for Direct Synthesis of Dimethyl Ether by Hydrogenation of Carbon Dioxide
|School||Harbin Normal University|
|Course||Physical and chemical|
|Keywords||amorphous catalyst copper-based catalyst rare earth oxide dimethyl ether|
Direct synthesis of dimethyl ether(DME) from carbon dioxide by catalytic hydrogenation is great economical and environmental importance, not only to synthesize the useful chemical products, which will utilize carbon dioxide more efficiently, but also to reduce the greenhouse effect resulting from carbon dioxide.The catalysts of single-step syngas-to-dimethyl ether were studied. By co-precipitation sedimentation preparation dimethyl ether synthetic catalyst part, with the mechanical mixing that mixed the methanol synthesis catalysts with methanol dehydration catalysts in the various ratio, and make catalysts reactivity in the fixed bed reactor.By chemical reduction method and impregnation method were prepared by the amorphous and conventional states of the two forms of the catalyst, and its carbon dioxide conversion and DME selectivity were investigated. The results shows that the amorphous copper based catalyst prepared by chemical reduction catalyst has good activity. When reaction temperature is 513 K, reaction pressure is 3 Mpa,1000 h-1 space velocity,94% conversion of carbon dioxide and dimethyl ether selectivity of 86% were obtained using amorphous catalyst Cu-ZnO-Al2O3/HZSM-5. The NH3-TPD analysis showed that the acidity of amorphous copper based catalyst bacame stronger than that of conventional catalyst prepared by impregnation method. However, the stability of hydrogenation of carbon dioxide using amorphous catalyst Cu-ZnO-Al2O3/HZSM-5 was bad. It is necessary to modify the amorphous catalyst Cu-ZnO-Al2O3/HZSM-5.The amorphous catalyst Cu-ZnO-Al2O3/HZSM-5 was modified by added 2%(mass fraction of catalyst) manganese oxide, zirconium oxide, lanthanum oxide and cerium oxide. The results showed that the modified catalysts show more stable than the unmodified catalyst. XRD analysis showed that the copper dispersion of modified catalyats increased. H2-TPR results showed that the interplay of CuO and supporter become stronger. The stability of amorphous catalyst Cu-ZnO-Al2O3-CeO2/HZSM-5 was investigated by follow reaction conditions:513K,3 Mpa, feed gas mixture carbon dioxide:hydrogen=1:4, reaction space velocity:1000 h-1. The results showed that the carbon dioxide conversion and DME selectivity change to a lesser extent within 20 hours, indicating better stability of the catalyst.