Cerium oxide, uses

Figure 2.31. Study of the crystallization of cerium oxide using a thermodiffraction system equipped with a curved position sensitive detector [BEN 96]...

An example of this method is shown in Figure 6.4. The sample is still the cerium oxide used for the international test [BAL 04]. This time, the diffraction peaks were fitted with Voigt functions. The result confirms that the increase in peak width for this sample is essentially due to the size effect. 

We have successfully synthesized pure and mixed manganese and cerium oxides using the surfactant assisted wet-chemistiy route followed by acidic treatment. The XRD analyses of calcined samples reveal the substitution of Ce" by Mn species in the fluorite structure forming a sohd solution with a solubihty limit of 50% Mn. For all the solids, the acidic treatment has important effect in the BET surface area. For the binary oxides a narrow pore size distribution was created after H2SO4 treatment, with a major extension for solids having high Mn content. 

The demand for the rare earth metals increased over the last two decades of the 20th century, and the demand for cerium oxides in motor vehicle catalytic converters (see equations 26.39 and 26.40) has been a major contributing factor. In 2001, the major use (34% of the total consumption) for rare earth metals in the US was in glass polishing and ceramics. Petroleum catalysts and catalytic converters... 

The above discussed results elucidate the mechanism of action of cerium oxide coatings as effective cathodes and of cerium ions (when they are present as a component of the corrosion medium) - as inhibitor having oxidative action, leading to improvement of the corrosion stability of stainless steels. They explain the improved ability of the steel to undergo passivation, respectively to recover its passive state in cases of disruption of its surface passive film - especially in this specific case, studied by us, i.e. disruption as a result of thermal treatment. 

The principle just outhned has two parts. The first part deals with redox processes and was developed here by examining the relative stabihties of the -i-2 and -i-3 oxidation states of the lanthanides. It can be extended in a variety of ways. Thus if the f variation is shifted one element to the right, it tells us the nature of the f variations, and accounts for the distribution of the -i-4 oxidation states of the lanthanides [2, 10, 15]. Their stability shows maxima at cerium(IV) and terbium(IV), decreasing rapidly as one moves from these elements across the series. 

The insight gained from exposure of 36 to oxidants led us to the successful work from the Flowers group utilizing a cerium-mediated oxidative allylation of vinylogous amides [42]. Their investigations used a more soluble source of Ce(IV)... 

Among electron carriers used for indirect oxidation reactions, cerium salts [Ce -t- e Ce E° = -t-1.44 V vs. NHE] appear to be of particular interest when a mild oxidation has to be considered. Substituted toluenes and methylaryl compounds are easily functionalized to the corresponding aldehydes in high yields [125-129]. Acidic solutions are required (such as aqueous AcOH, aqueous methane sulfonic acid, or aqueous trifluorosulfonic acid). The conversion of aromatic compounds into quinones may also be conducted by means of electrogenerated ceric ions (see Table 3). Let us stress the example... 

A variety of organic compounds are oxidized by salts of polyvalent metals. We have already discussed one-electron oxidations by some Lewis acids and noted that the mechanisms of these oxidations are unknown. In contrast, oxidations by some other metal salts have been studied quite thoroughly and much is known about the mechanisms. Of particular interest to us are cobalt(III), man-aganese(III), lead(IV), and cerium(IV) salts, and the most commonly used are the acetates. Another contrast with the Lewis acids is that cation radicals formed in oxidations by salts of polyvalent metals usually have short lifetimes since they are involved in further... 

Broeker, J.L., Partenheimer, W, and Rosen, B.I. (1995) Process for the manufacturing of aromatic dicarboxylic acids utilizing cerium to facilitate a low bromine to metals catalyst ratio. US Patent 5,453,538, Sept 26, 1995. Broeker, J.L. and Gong, WH. (1996) Low bromine />-xylene oxidations. 6th International Symposium on the Activation of Dioxygen and Homogeneous Catalytic Oxidation, Noordwijkherhout, The Netherlands, April 14-19,1996. 

Preparation of ammonia synthesis catalysts by the treatment of a reduced iron oxide with an aqueous solution of a cerium salt. (Lummus Co.). US 3992328 (1976) GB 1479310 (1977). 

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