Characterization of Silica-Supported Cobalt Catalysts Prepared by Decomposition of Nitrates Using Dielectric-Barrier Dis
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Characterization of Silica-Supported Cobalt Catalysts Prepared by Decomposition of Nitrates Using Dielectric-Barrier Discharge Plasma Chengdu Huang • Suli Bai • Jing Lv Zhenhua Li
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Received: 3 March 2011 / Accepted: 17 May 2011 / Published online: 1 June 2011 Ó Springer Science+Business Media, LLC 2011
Abstract Low temperature decomposition of precursors usually leads to higher cobalt dispersion. In this study, we present a method to decompose cobalt precursors by using dielectric-barrier discharge (DBD) plasma without requiring a thermal calcination process. Cobalt (Co) catalysts prepared by DBD plasma were characterized by a range of techniques. The results indicate that the DBD decomposition method can not only reduce the decomposition time but also achieve an increased Co dispersion, small Co3O4 cluster size and uniform distribution compared to traditional calcination method. It was observed that the DBD-treated catalysts performed well in Fischer–Tropsch synthesis and were favorable for heavy hydrocarbon formation. Keywords Cobalt catalyst Cold plasma Precursor decomposition Fischer–Tropsch synthesis
1 Introduction Fischer–Tropsch (FT) synthesis can be used to convert coal, natural gas or biomass-derived syngas to clean fuels and chemicals [1–3]. Cobalt (Co) catalysts are the preferred catalysts for low-temperature FT synthesis because of their high reactivity, selectivity for linear C5? hydrocarbons, and Electronic supplementary material The online version of this article (doi:10.1007/s10562-011-0627-x) contains supplementary material, which is available to authorized users. C. Huang S. Bai J. Lv Z. Li (&) Key Lab for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China e-mail: [email protected]
low reactivity for the water–gas shift reaction. In addition, they have an increased stability towards deactivation by water and are more affordable compared to noble metals. Iglesia et al. [4] reported that the FT reaction rate depends on the number of cobalt metal surface sites. High volumetric cobalt metal site densities lead to increased activity and C5? selectivity. The synthesis of highly dispersed Co catalysts requires the initial formation of very small CoO or Co3O4 crystallites. The Co catalysts were typically prepared by using incipient wetness impregnation, which is the most frequently used method due to its simplicity, cost efficiency, and limited waste production. Furthermore, aqueous cobalt nitrate (Co(NO3)2), used as a precursor solution, is attractive not only because it enables the preparation of highly loaded catalysts by single-step impregnation, but its nitrate can be easily removed through combustion, which leaves no impurities. The structure of the final Co catalyst is a result of the whole preparation procedure; however, decomposition of impregnated cobalt precursors has a significant influence on the performance of the catalyst [5]. According to Girardon et al. [6], significantly increased C
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