Study On Cr-Based Catalysts Over The Oxidative Dehydrogenation Of Ethane With CO₂ To Ethene

The processes of catalytic conversion of ethane to ethelene by oxidative dehydrogenation are of increasing importance because of growing demand for ethene. As one of the major greenhouse gases, carbon dioxide can also act as a mild oxidant. Utilization of carbon dioxide in the oxidative dehydrogenation of ethane reactions can retard greatly coke deposition on the catalysts surface and enhance ethane conversion and ethene selectivity.In this investigation, a series of the xCr-yCe/SiO₂-G catalysts with different chromium and cerium content were prepared by sol-gel method using chromium nitrate as chromium source, cerium nitrate as cerium source and tetraethyl orthosilicate (TEOS) as silica source.xCr-yCe/SiO₂-G/Al₂O₃/FeCrAl structured catalysts were prepared using FeCrAl alloy foils as support, Al₂O₃ as washcoat layer and xCr-yCe/SiO₂-G as active component. The structures of the catalysts were characterized using XRD, BET and TPR techniques. The catalytic performances for the oxidative dehydrogenation of ethane to ethene with CO₂ were evaluated in a fixed-bed micro-reactor.The results of the catalytic activity shown that, for xCr/SiO₂-G catalysts, the 5Cr/SiO₂-G catalyst was the best for the oxidative dihydrogenation of ethane. The selectivity of ethene was very high for the yCe/SiO₂-G catalysts, and 10Ce/SiCVG catalyst has the highest conversion of ethane. xCr-yCe /SiO₂-G/Al₂O₃/FeCrAlCr metal based monolithic catalysts has good activity and high-temperature stability. To compare with the xCr/SiO₂-G catalysts, the conversion of ethane was decreased and the selectivity of ethene was increased for the Cr-10Ce/SiO₂-G/Al₂O₃/FeCrAlCr catalysts. And 7.5Cr/SiO₂-G/Al₂O₃/FeCrAlCr catalyst exhibited an excellent stability at 750℃.The results of the structural characterization of the catalysts indicated that Cr species were presented in Cr₂O₃ phase when the Cr content was above 5%. There were no any Cr species phase with lower Cr content in the catalysts. The 5Cr/SiO₂-G catalyst had the biggest BET surface area. The pore diameter of catalyst was 2 nm. The redox properties of the catalysts were the key of the catalytic activity. However, Cr and Ce were dispersed differently in xCr -10Ce/SiO₂-G because CeO₂ can promote dispersion of the Cr species. For Cr-10Ce/SiO₂-G/Al₂O₃/FeCrAl, the activity species of catalysts were well dispersed on the surface of metallic support.