Study On The Catalysts For CO₂ Oxidative Dehydrogenation Of Ethane To Ethylene

Ethylene is one of the most important substances for chemical industry. With the development of the world economy, the demand for ethylene is growing. Using mild oxidant greenhouse gas CO₂, selective oxide dehydrogenation of ethane to ethylene is a new idea. Compared with the high-temperature vapor used for dehydrogenation medium, CO₂ not only played the role of mild oxidant in the reaction, but also system thinner. The reaction of direct dehydrogenation of ethane broke through the restrictions of thermodynamic equilibrium by introduction of CO₂ and greatly improving the yield of ethylene. The selectivity of target product and compound gas (CO + H2) by-product are raised by the effective suppression of deep oxidation about intermediate product. When given the same ethylene yield, the introduction of CO₂ as a reaction materials not only could reduces the reaction temperature, could save the energy of the follow-up distillation process, reduce emission of greenhouse gas, but also achieve the transform and use of carbon resources. At the same time, the refining and circle of CO₂ is easy to be refined circularly, many of the oil Vice-chemical process is a high concentration of CO₂ industrial exhaust gas could be produced in many petrochemical process.In this work, a series of supported chromium-based catalysts were prepared by impregnation method. The catalysts were characterized by means of XRD, BET, TPR, XPS, UV-Vis and TPD etc. to establish a relationship between the structure, surface acidity, redox properties of the catalysts and the catalytic performance. Meanwhile, the nature of active sites, the reaction mechanism and the reason for deactivation were also discussed. The main experimental results and conclusions are as follows:1. Study on the Cr-CoAl₂O₄/Al₂O₃ catalysts which modified by CoAl₂O₄ for CO₂ oxide dehydrogenation of EthaneImpregnation ofγ-Al₂O₃ with Co and Al nitrates formed CoAl₂O₄ on the support. Effect of the molar ratio of Cr or Co toγ-Al₂O₃ on the structure and catalytic activity was studied. The results showed that 14%Cr-4%CoAl₂O₄/Al₂O₃ catalyst has the highest catalytic activity in the 973K, ethane conversion rate was 35.0%, 32.5% yield of ethylene, ethylene selectivity is 92.5%. XRD, UV-Vis and TPR The results of XRD, UV-Vis and TPR show that Co existed on the support in the form of spinel CoAl₂O₄ after baking at 900°C. The XPS outcome indicate that there are two valence Cr on the catalysts which are Cr(â…¢) and Cr(â…¥). Meanwhile, it show that the combination of Cr ions reduced after modified by spinel CoAl₂O₄. this means the binding energy between Cr and Al decreased, but the ratio of Cr(â…¥) to Cr(â…¢) increased, this is the main reason for increasing of catalytic activity. By DTA-TGA testing, the quantity of coke decreased, but the type of coke was not changed, those also showed the CoAl₂O₄ has some restrained function on coke.2. Study on the Cr-NiAl₂O₄/Al₂O₃ catalysts which modified by NiAl₂O₄ for CO₂ oxide dehydrogenation of EthaneSeries Cr-NiAl₂O₄/Al₂O₃ supported catalysts were prepared by an impregnation method, and these catalysts were characterized by many kinds of means. The TPR and DRS UV-Vis results showed that there are two kinds of forms on the catalysts which are NiO and NiAl₂O₄. The CO₂-TPD results indicated that the adsorptive quentity were increased with entering Ni. 14%Cr-2%NiAl₂O₄/Al₂O₃ catalyst has the biggest adsorptive quentity. It has the same rule with catalytical activity. The 14%Cr-2%NiAl₂O₄/Al₂O₃ catalyst has the highest catalytic activity in the 973K, ethane conversion rate was 33.0%, 31.0% yield of ethylene, carbon dioxide conversion rate was 22.0%.