Putting Depleted Uranium to Use: A New Class of Uranium-Based Catalysts
The US Department of Energy has more than a billion lbs of depleted uranium (DU) in stockpiles. The DU is mostly in the form of UF6 stored in barrels in Oak Ridge, TN and Portsmouth OH. UF6 is volatile and corrosive and must be converted to a more stable form in the future. The costs of conversion are immense. Technologies which utilize uranium in large quantities or in a high value application are required to finance the expense of stockpile conversion.
Uranium oxide has shown promise as a
catalyst for oxidation of volatile organic compounds (VOCs) and halogenated VOCs.
(Hutchings 1996). U.S. industries
and the U.S. Department of Energy must manage a variety of off-gas wastes
consisting of complex volatile organic compounds.
Development of uranium catalysts for combustion of VOC and
HVOCs offer the possibility of utilizing uranium in a high value
application which solves two problems
Our group, in collaboration with Sheng Dai
of the Chemical Technology Division, is investigating a new class of mesoporous
uranium oxide and mesoporous sol-gel catalysts doped with uranium oxides for
destruction of a range of volatile organic contaminants, including alkanes,
aromatics, and chlorinated organic compounds.
This research will contribute to a fundamental understanding of the
mechanism and rate-limiting processes that control the reactivity and
selectivity between uranium-based catalysts and the organic substrates (or
Synthesis of catalysts
Mesoporous materials, first synthesized by
researchers at Mobil Research Labs (Beck, 1992) can be grown to have very well
ordered and uniform size distributions. The
micrograph in Fig. 1 shows a mesoporous silica, MCM-41, we synthesized using
cetyltrimethylammonium bromide (CTAB) as a sufactant template molecule. Various
mesoporous catalysts have been synthesized using CTAB and other surfactants
which contain uranium (uranyl
nitrate) introduced directly into the silica based sol-gel synthesis.
MCM-41 support impregnated with uranium nitrate has also
been produced for comparison. The
materials have been characterized by BET surface area measurements to determine
surface area and total pore volume.
Figure 1 - TEM of MCM-41
Catalytic properties of DU
Figure 2 - Conversion of Toluene vs Reaction Temperature
The best catalyst in terms of high toluene conversions at low temperatures was a sample prepared by solution impregnation of uranyl nitrate into a previously prepared silica mesoporous material, MCM-41 (indicated as U-MCM-41 in Fig. 2), followed by calcination to 800 °C. This sample was prepared to mimic those used by Hutchings et al. [Nature 384 1996, 341-343] except that mesoporous silica was used instead of fumed silica.
Figure 3 - Optical absorption spectrum obtained in reflectance mode for UCT2B.
Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T.-W.; Olsen, D. H.; Sheppard, E. W.; McCullen, S. B.; Higgins, J. B.; Schlenker, J. L., J. Am. Chem. Soc. 114 (1992) 10834.
Hutchings, G. J.; Heneghan, C. S.;
Hudson, I. D.; Taylor, S. H., Nature 384
Revised: 8 - August - 2002 by David R. Mullins