Preparation and Characterization of Fibrous Cerium Oxide Templated from Activated Carbon Fibers
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Preparation and Characterization of Fibrous Cerium Oxide Templated from Activated Carbon Fibers Mark Crocker, Uschi M. Graham, Rolando Gonzalez, Erin Morris, Gary Jacobs and Rodney Andrews University of Kentucky Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511, U.S.A.
ABSTRACT High surface area cerium oxide has been prepared using a carbon templating method. Impregnation of a highly mesoporous activated carbon (Darco KB-B) with an aqueous solution of cerium nitrate, followed by carbon burn off, afforded ceria with surface area of up to 148 m2/g. According to thermogravimetric studies, ceria formation proceeds via decomposition of cerium nitrate at ca. 410 K; oxidation of the carbon template commences at the same temperature, being facilitated by the release of NO2 from the Ce compound. Use of activated carbon fibers (ACFs) as template was found to provide a simple route to fibrous cerium oxide. The lower surface areas (3 - 59 m2/g) of the resulting ceria fibers reflect the largely microporous nature of the ACFs; evidently the Ce nitrate solution is unable to penetrate their micropores. Consequently, the surface area of the ceria product is found to increase with increasing mesoporosity of the ACF template. Electron microscopy reveals that the ceria fibers are composed of highly crystalline primary particles of 5-10 nm diameter; further, the fibers display a number of interesting morphological features at the macro- and nano-scales.
INTRODUCTION Cerium oxide is employed as a catalyst or catalyst promoter in a number of important chemical processes, including the elimination of pollutants from auto-exhaust gases using threeway catalysts, fluid catalytic cracking in refineries, and the dehydrogenation of ethylbenzene to styrene [1-3]. Ceria also shows promise as a catalyst component for low temperature water-gas shift applications [4], and the preferential oxidation of CO in hydrogen-rich atmospheres (PROX) [5]. In these various applications, the performance of the ceria is strongly dependent on its crystallinity and textural properties, including surface area and porosity. In this context, we are studying the preparation of high surface area cerium oxide using a carbon templating method. This approach has been successfully used for the synthesis of a number of high surface area metal and mixed metal oxides, using amorphous activated carbon [6-8], activated carbon fibers [8-10], or carbon spheres [11-13] as the template. The preparation of metal oxide nanorods and nanotubes from carbon nanotubes has also been described [14,15]. However, the preparation of high surface ceria using carbon templating does not appear to have been studied to date. This fact, coupled with our interest in preparing high surface area ceria for use as a component in water-gas shift catalysts, prompted the present study.
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EXPERIMENTAL DETAILS Activated carbon fibers were prepared by thermal activation of P-400 Ansham fibers under a flow of steam/N2 at 1073-1173 K for periods of between 1 and 3
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