Konduru, M.V.

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Novel Mesoporous Uranium-Oxide Based Catalysts for Removal of Volatile Hydrocarbons and Chioro-Organic Compounds: Synthesis and Reactivity Studies Mahesh V. Konduru+, Erin Myers*, Sheng Dai*, and Steven H. Overbury+ + Chemical and Analytical Sciences Division, Oak Ridge National &&ordov, p.0. Ra 2008, MS 6201, Oak Ridge TN 3 7831 * Chemical Technology Division, Oak Ridge National Laboratory, P. 0. Box 2008, MS 6181, 1. Introduction Oak Ridge TN37831 Catalytic combustion of volatile hydrocarbons and chloro-organic compounds at 10~ temperatures provides an environmentally benign as well as an energy efficient route for their removal. The removal of chloro-organic compounds has been reported to occur at moderate temperatures (x673 K) with the use of supported and unsupported uranium-oxide-based catalysts that exhibit exceptionally high activity (I). The highly active uranium-oxide-based catalysts, synthesized by conventional catalyst preparation techniques, are nonporous materials where the bulk of the uranium-oxide catalysts may not be involved in the reaction The use of molecular assemblies of surfactants or related substances as structure directors has led to the synthesis of highly ordered mesoporous ahnninosilicates and various transition metal oxides with very high surface areas (Z-4). These methods have been used in the present study for the synthesis of novel mesoporous supported and unsupported uranium-oxide-based catalysts that should exhibit exceptionally high activity for the thermal oxidation of volatile hydrocarbons and chloro-organic compounds. The synthesis and use of ordered porous uranium-oxide-based catalysts would not only- greatly enhance the catalyst efficiency chioro-organic compounds but also provide an effective approach for the utilization of for the destruction of volatile hyhrocarbon and large amnunts of., depleted llEaDiurn from ‘,‘. ,,-.. nuclear fuel production. II 2. Catalyst Syntheses Two types of catalysts have been synthesized in the present study: (1) U308 supported by mesoporous SiOl (UsO$SiO2) and (2) mesoporous uranium oxide (&OS). U3O$SiO2 was synthesized by preparing a mixture of 0.12 cetyltrimethylammonium bromide (CTAB): 0. I uranium nitrate: 1.0 tetramethylorthosilicate (TMOS): 1.0 methanok0.02 HNOs: 4&O. The resulting solid was heated in air at 873 K to obtain the mesoporous U&&02. The U&s catalyst was prepared by mixing CTAB and UC14 (CTAEVUC~=O. 16) in water. NE&OH was added to adjust the pH to 10. The solution ’ To whom the correspondence should be addressed. Figure 1 Transmission electron micrograph of . mesoporous SiOz showing hexagonally packed mesopores. “The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. DOE-AC05-OOOU22725. Accordingly, the U.S. Government retains a nonexclusive, roplty+ec license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.’ was filtered and the soiid filtrate calcined in air at 723 K to obtain mesoporous U308. 3. Results The transmission electron micrograph (TEM) of mesoporous SiOz prepared without the addition of the uranium precursor is shown in Figure 1. SiOz with hexagonally packed pores. The synthesis produced a highly ordered Bnmu~ Emmitt ‘Teller (BET) analysis performed on U308/Si02 revealed a surface area of 310 m2/g with a maximum pore diameter of 72 11 In addition, Nz-adsorption/desorption isotherms indicate that the pores are mesoporous with a fairly narrow distribution. The surface area, pore sizes, and pore size distribution for the mesoporous U308 catalysts were also measured and are listed in Table 1. The surface area of U308 obtained from the present study is significantly greater (65O:l) than that of a commercially available u308. Table 1 Comparison of Surface Area and Pore Diameter of Mesoporous Uranium oxide Catalysts Catalyst Surface Area (m”/g) Pore Diameter (A) Mesoporous U3O$SiO2 310 72.0 Mesoporous Us08 65 114.7 . u308 (commerd) 0.1 The determination of catalytic activity and selectivity of these catalysts for the removal of’ toluene and chlorobenzene is currently underway. Future studies will aim at understanding the adsorption/desorption of reaction intermediates and the role that these intermediates play in the catalytic oxidation of volatile organic and chloro-organic compounds. Research sponsored by the OfEce of Nuclear Energy, Science and Technology, U.S. Department of Energy, under contract DE-ACO5OOOR22725 ,with O$c Ridge National Laboratory, managed and operated by UT-Battelle, LLC. ‘. ..I ,r: .“M:xr & mv %n ~zppointment to the Oak Ridge National Laboratory Postdoctoral Research Associates Program administered jointly by the Oak Ridge Institute for Science and Education and Oak Ridge National Laboratory. 4. References 111 E21 [31 G. J. Hutchings, C. S. Heneghan, I. D. Hudson, and S. H. Taylor, Nature 384 (1996) 341. C.TKresge, M. E. Leonowicz, W. J. Roth, J. C. Varhdli, and J. S. Beck, Nature 359 (1992) 710. A. Firouzi, D. Kumar, L. M. Bull, T. Besier, P. Sieger, Q. Huo, S. A. Wa&er, J. A. Zadh&i, C. Glinka, J. Nicol, D. Margolese, G. D. Stucb, and B. F. Chemelka, Science 267 (1995) 1138. 141 P. Yang, D. Zhao, D. I. Margokse, B. F. Chemellca, nd G. D. Stucky, Nature 396 (1998) 182. 

Novel Mesoporous Uranium-Oxide Based Catalysts for Removal of Volatile Hydrocarbons and Chloro-Organic Compounds: Synthesis and Reactivity Studies

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Novel Mesoporous Uranium-Oxide Based Catalysts for Removal of Volatile Hydrocarbons and Chloro-Organic Compounds: Synthesis and Reactivity Studies

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