Study On Preparation And Performance Of Cr/Na-ZSM-5 Catalysts

Ethylene is a basic material for the world’s petrochemical industry,used in many important chemical products. It is the main raw material for the production of polyethylene, ethylene oxide and ethylene dichloride. Ethylene is primarily produced from petroleum via cracking. However, the depletion of crude oil has stimulated the development of non-petroleum routes for the production of ethylene. Recently, ethane oxidative dehydrogenation(ODHE) attracted the attention of many scholars. Compared with the traditional ethane cracker path, oxidative dehydrogenation not only save energy, but the operation more flexible, and environmentally friendly [1]. There are a rich feedstock source of ethane, oxidative dehydrogenation is an exothermic reaction and can be performed at moderate temperatures(< 773 K) with high C2H6 conversions. At the same time, use CO2 as a mild oxidant can effectively alleviate the depth oxidation of the reaction product. So, oxidative dehydrogenation of ethane to ethylene is one of the highly attractive routes [2].The ZSM-5(H-form) of Si/Al ratio equal to 40 was modified with sodium cations by means of exchange procedure from a certain concentration of NaNO3 aqueous solution. We prepared three kinds of carriers with different switching frequency, and then used modified Na-ZSM-5 as a carrier, prepared two series of xCr/Na-ZSM-5 and yCe-7.5Cr/Na-ZSM-5 catalysts by impregnation. Combined FT-IR, XRD, TPD results, the adsorption capacity to CO2 of the carriers that calcined at 873 K enhanced with the modified number increased at a high temperature, and the bits number of alkaline increased, the alkali bits temperature was gradually lowered, but the structure of the carrier didn’t changed. For xCr/Na-ZSM-5 catalyst, with the addition of Cr Species, the acid-base distribution on the catalysts’ s surface and oxidation capacity were changed. The maximum C2H6 conversion and C2H4 yield can be achieved on the 7.5Cr/Na-ZSM-5 catalyst, were 12.07% and 14.16% respectively when the reaction conditions were 1023 K, Vco2/Vc2H6=3. The addition of Ce species obviously improved the dispersion of Cr species on yCe-7.5Cr/Na-ZSM-5 catalysts, and increased the reducibility of chromium and the ratio of Cr6+/Cr3+, increased the activity and stability of the catalysts, reduced the amount of carbon deposition on the catalysts surface. When the reaction conditions were 1023 K, Vco2/Vc2H6=3 and the Ce loading was 7.5%, the catalytic activity has obviously enhancement, 19.97% C2H6 conversion and 19.11% C2H4 yield can be obtained on the 7.5Ce-7.5Cr/Na-ZSM-5 catalyst.