Lithium ion-exchanged zeolite faujasite as support of iron catalyst for Fischer-Tropsch synthesis
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Catalysis Letters, Vol. 114, Nos. 3–4, April 2007 (Ó 2007) DOI: 10.1007/s10562-007-9062-4
Lithium ion-exchanged zeolite faujasite as support of iron catalyst for Fischer-Tropsch synthesis Ping Wang, Jincan Kang, Qinghong Zhang, and Ye Wang* State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P.R. China
Received 22 November 2006; accepted 16 January 2007
Among various microporous and mesoporous materials investigated, the Li+-exchanged zeolite faujasite has been found to be the most efficient support of iron catalyst for producing C5+ hydrocarbon fuels via Fischer-Tropsch synthesis. The location of iron species in the catalyst is a key issue in obtaining high selectivities to C5+ hydrocarbons. It is proposed that the Li+ cation and the supercage structure of zeolite faujasite both play important roles in improving the selectivities to C5+ hydrocarbons over the Fe catalyst. KEY WORDS: Fischer-Tropsch synthesis; iron catalyst; lithium; zeolite faujasite; C5+ hydrocarbons.
1. Introduction Fischer-Tropsch (FT) synthesis is a key reaction for the transformation of synthesis gas, which can be derived from natural gas, coal, or biomass, into hydrocarbon fuels. Researches on catalyst development for the production of hydrocarbon fuels based on FT synthesis have attracted renewed attention because of the urgent demand for the decrease in the dependency on oil [1,2]. Moreover, the hydrocarbon fuels produced in FT synthesis can be sulfur-free and ultra-clean, and may easily meet the stringent environmental requirements [2,3]. However, because FT synthesis usually follows the Anderson-Schultz-Flory product distribution, the design of catalysts with desired product selectivities remains a critical challenge [4–7]. Many recent studies have indicated interestingly that the utilization of microporous or mesoporous materials, which possess ordered porous structures, as catalyst supports can modify the product selectivities for the cobalt-catalyzed FT synthesis [8–15]. Moreover, interesting size effects of cobalt particles on activity and C5+ selectivity have recently been reported using carbon nanofiber-supported catalysts [16]. These studies have provided insights into the design of new Fischer-Trospch catalysts with improved activity and tunable product distributions. On the other hand, similar studies are very few for the iron-catalyzed FT synthesis. Because of the lower cost and some distinct features such as wider operation ranges of temperature and H2/CO ratio, Fe-based *To whom correspondence should be addressed. E-mail: [email protected]
catalysts could provide an attractive complement to Co-based catalysts for the purpose of producing ultraclean hydrocarbon fuels via FT synthesis [17–20]. However, as compared with Co catalysts, Fe-based catalysts usually exhibit higher selectivities to CO2 because of the higher activity toward the water gas shift reaction. This may lead to 30–50% of the carbon feed being rejected as CO2 in some cases
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