Precursors uranium oxides

In a much earlier patent, the removal of organics from exhaust gases by oxidation over a supported uranium oxide catalyst was reported by Hofer and Anderson [39]. The catalyst was 4% U3O8 supported on alumina spheres. The authors used the incipient wetness technique to impregnate alumina with uranyl nitrate solution. In this case the catalyst precursors were calcined at 700°C for 3 h to decompose the uranium salt. The use of other uranium compounds as starting materials was mentioned and these included uranyl acetate, uranium ammonium carbonate and uranyl chloride. The alumina-supported catalyst had a surface area of ca 400m g and further added components, such as copper, chromium and iron, were highlighted as efficient additives to increase activity. 

The first and thus far only silsesquioxane complex of an actinide element is [Cy7Si70i2]2U (100). This colorless, nicely crystalline uranium(VI) compound is formed upon reaction of 3 with any uranium precursor, e.g., UCI4 in the presence of NEt3. In all cases oxidation of uranium to the hexavalent oxidation state is observed. The best synthetic route leading to 100 in ca. 80% yield is the reaction of 3 with uranocene as outlined in Scheme 33. 

I he atomic wcighi varies because of natural variations in the isotopic composition of the element, caused by the various isotopes having different origins - I h is the end product of the thorium decay scries, while Ph and " Pb arise Irom uranium as end products of the actinium and radium series respectively. Lead-204 has no existing natural radioactive precursors. Electronic configuration l.v 2s lfc22/j"3v 3//,3i/l"4v- 4/, 4l/" 4/ IJ5v- 5/ "5t/l"bv />-. Ionic radius Pb I.IX A. Pb 1 0.7(1 A. Metallic radius 1.7502 A. Covalent radius (ip i 1.44 A. First ionization potential 7.415 cV second. 14.17 eV. Oxidation... 

Schiff base and related complexes of uranium and thorium are widely described in recent literature and covered in a review [463]. Those of U(VI) have a practical use as catalytic organic oxidants [460] or as part of a polystyrene-supported chelating resin [464,465]. Among other Schiff base precursors, salicylaldehyde [466] and triethylenetetramine [464], 3-formylsalicylic acid and o-hydroxybenzylamine [465], or salicylaldehyde and l-amino-2-naphthol-4-sulfonic acid [467] were used. In the example of Schiff base complexes, kinetics of formation of U(VI) complexes and their pK values were studied [468]. 

Ceramic membranes were first developed in the 1940s for uranium isotope enrichment processes. Important progress has been made since that time, mainly due to the improved knowledge of the physicochemical properties of the membrane precursors. Most CMR studies concern alumina membranes other oxides such as silica, titania, or zirconia are much less frequently mentioned. 

Ethers, cyclic ethers. The complex UCl3(THF) was reported by Moody et al and subsequently used by a number of researchers as a precursor for entry into chemistry. The molecular nature of the complex was not well characterized, however. Subsequently, the complex Ul3(THF)4 was prepared via halide oxidation of uranium metal and structurally characterized. The metal center is found to lie within a pentagonal bipyramidal coordination environment, with... 

Uranium trioxide is a key precursor to UF4 and UFg, which are used in the isotopic enrichment of nuclear fuels. It is also used in the production of UO2 fuel, and microspheres of UO3 can themselves be used as nuclear fuel. Fabrication of UO3 microspheres has been accomplished using sol-gel or internal gelation processes.Finally, UO3 is also a support for catalytic oxidative destructive of organics. 

Edehnann etal. recently reported the reaction of disilanol (32) with Ce [N(SiMe3)2]3 in the presence of excess pyridine to surprisingly produce the product of oxidation, heptacoordinate cerium(IV) siloxide (33), in yields of 67% (Scheme 7). Interestingly, the low oxidation state uranium precursors, (C0T)2U (COT = yjg-CgHg), and UCI4 react with... 

R7Si709(0H)3, (4), to generate the homoleptic uranium(VI) siloxide [R7Si70i2]2U exclusively upon oxidation. Although the identity of the oxidizing agent remained unclear (no elemental oxygen was present), tliis type of oxidative silanolysis of cerium(III) precursor compounds could provide a convenient synthetic alternative in the synthesis of various homo- and heteroleptic cerium(IV) siloxides. 

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