Oxidative Dehydrogenation Of Ethane With Carbon Dioxide To Ethylene-the Study Of Supported Chromium Oxide Catalysts And The Catalytic Process At Low Temperature

Oxidative dehydrogenation of ethane (ODE) with carbon dioxide to ethylene is one of promising routes for the conversion of C2H6 into highly value chemicals. Carbon dioxide as a mild oxidant could participate in the dehydrogenation of C2H6 and increase the conversion of C2H6 and the yield of C2H4. In the present paper, the reaction performance of ODE with CO2 to C2H4 over different catalysts was investigated and found some catalysts which have the good reaction performance of the reaction. In order to avoid the effect of non-catalytic reaction during the catalytic reaction of ODE with CO2 to C2H4, we investigated the catalytic process at low temperature and gave an understanding of this catalytic process, for example, the role of CO2 in the dehydrogenation of C2H(, to C2H4, the active species on the catalyst, the coking behavior of the catalyst and the reason of catalyst deactivation. The focus is on the reaction performance of the oxidative dehydrogenation of C2H6 to ethylene at 923K and found that the 6Cr/AC and 6Cr/Si02 catalysts had the good performance of the reaction. It was the first report about 6Cr/AC catalyst here. The ODE with CO2 to C2H4 over the chromium oxide catalysts supported on different supports was investigated at 923K. It was shown that the dispersion of chromium oxide on the catalyst and the acidity/basicity of the catalyst had an effect on the catalytic activity of the reaction. The suitable acidity of the catalyst was favorable to the activity of the reaction. The effect of the dispersion of chromium oxide on the catalyst was of importance for C2H6 activation. A higher dispersion of chromium oxide on the catalyst gave a better reaction performance of the ODE with CO2 to C2H4. II ABSTRACT_ It is confirmed that the presence of carbon dioxide indeed enhanced the conversion of C2H6 based on thermodynamic equilibrium. Moreover, in our experiment, the effects of CO2 on the dehydrogenation of C2H6 over different catalysts were investigated. The results showed that the effects of CO2 were different over different catalysts. Carbon dioxide exerted promoting effects on the dehydrogenation of C2H6 over AC and Si02 supported chromium oxide catalysts, while carbon dioxide had the adverse role over 6CrIMCM4 1 and 6Cr/y-A1203 catalysts. EPR characterization of the Cr species on the 6Cr/Si02 catalysts pretreated with H2 or 02 was extensively studied, and it was found that in the beginning of the reaction, C21-16 reduced the Cr5~ and Cr6~ species accompanied by the formation of Cr> and Cr> species for the oxidized catalyst; CO2 oxidized the Cr2~ and Cr拁 species to Cr5 and Cr64 species for the reduced catalyst. However, whatever the oxidized fresh catalyst and the reduced fresh catalyst, Cr species on the catalyst could reach the stable state after a period. At this time Cr2 and Cr~ species were proposed to be the predominant species on the catalysts and they could be taken as the stable active species for the reaction. After the reaction reached the stable state, the reaction mechanism was mainly the catalytic dehydrogenation of C2H6 to C2H4 over the active species. The coking behavior of the 6Cr/S iO2 catalyst and the decoking behavior of CO2 and the reason of the catalyst deactivation were characterized by on-line TPO, EPR and TG methods. The reaction temperature determined the species of the coke on the catalyst after the reaction of ODE with CO2. Only an amorphous coke was form...