Oxidation of cerium

Cerium Oxide. The most stable oxide of cerium is cerium dioxide [1306-38-3] Ce02, also called ceria or ceric oxide. When cerium salts are calcined in air or if oxygen is present, this tetravalent Ce(IV) oxide is formed, cerium sesquioxide [1345-13-7] can be prepared in strongly reducing... 

Cerium(III) also proved to be an effective inhibitor of the oxidation of formic acid. As the oxidation of cerium(rri) to cerium(IV) is a 1-equivalent process, the inhibition furnishes additional evidence for the chromium(IV) species as intermediate. 

There are two oxides of cerium with oxidation states of 3 and 4. Cerium can also react with fiuorine and chlorine. 

In 1923 CeC>2 was found to have the fluorite structure (Goldschmidt and Thomas-sen, 1923), and in 1926 PrC>2 was found to have the same structure (Goldschmidt, 1926). In 1950 the intermediate compositions in the PrO system were reported to have the fluorite structure of variable lattice parameters (the superstructure reflections were not observed). In 1951 TbC>2 was also shown to have the fluorite structure (Gruen et al., 1951). By this time the basic fluorite structure had been established for all the known higher oxides of cerium, praseodymium and terbium. 

The mixed rare earth oxides containing cerium can be separated by oxidation of cerium to cerium(IV) by hypochlorite. 

There have been a few studies on the surface oxidation of cerium. Oxidation of cerium has been studied by UV photoelectron spectroscopy [48] and XPS [49]. From these studies, the formation of Ce203 on the surface of the metal has been concluded along with evidence for... 

Lanthanide chemistry started in Scandinavia. In 1794 Johann Gadolin succeeded in obtaining an earth (oxide) from a black mineral subsequently known as gadolinite he called the earth yttria. Soon afterwards, M.H. Klaproth, J.J. Berzelius and W. Hisinger obtained ceria, another earth, from cerite. However, it was not until 1839-1843 that the Swede C.G. Mosander first separated these earths into their component oxides thus ceria was resolved into the oxides of cerium and lanthanum and a mixed oxide didymia (a mixture of the oxides of the metals from Pr through Gd). The original yttria was similarly separated into substances called erbia, terbia, and yttria (though some 40 years later, the first two names were to be reversed ). This kind of confusion was made worse by the fact that the newly discovered means of spectroscopic analysis permitted misidentifications, so that around 70 new elements were erroneously claimed in the course of the century. 

The synthesis and preliminary X-ray structure of the first organometallic Ce(IV) complex Ce(CsH8)2 was reported in 1976 [115] and reproduced in 1985 [116] by the reaction of cerium(IV) isopropoxide with triethylaluminum in the presence of cyclooctatetraene, as shown in Figure 8.35. The accurate sandwich molecule structure of cerocene has been eon-firmed by an X-ray structural study on the methyl substituted cerocene [Ce(MeCOT)2] [117], Subsequently, two more substituted cerocene analogs have been synthesized via a more efficient method, for example, controlled oxidation of cerium(III) precursors and one of these complexes has been structurally characterized [118],... 

Higher interaction of oxygen molecules with CeX may be explined in terms of interaction of oxygen molecules with non-stochiometric oxides of cerium probably formed inside zeolite cavities due to interaction of cerium with zeolitic firework oxygens. Cerium is known for its non-stochiometric oxides, which are oxygen selective. 

In the soil the lanthanides are immobile under a wide variety of pH conditions, due to the low solubility of salts such as carbonates and phosphates. ConcenU ations in ground water are much lower than those of the soil through which the water percolates. In most natural waters, because the lanthanides sorb strongly to silicates and humic material, the bulk of the Ln content including cerium is associated with such colloidal particulates [44]. In the marine environment a depletion of cerium relative to the other lanthanides is found that is attributed to the oxidation of cerium (III) to highly insoluble Cc(IV) (OHjj-type species. 

There has been a strong effort to rationalise and elucidate a structural principle which will account for all the anion-deficienl, fluorite-related, mixed-valent binary oxides of cerium, praseodymium and terbium. This is a key step not only for the solid-state chemistry of these materials but also for a large class of fluorite-related materials involved in applications such as fast oxygen conductors and as catalysts. The two main theoretical approaches to the problem were developed by Martin and by Kang and Eyring, and will be illustrated in the following sections. 

In preparing fine particles of inorganic metal oxides, the hydrothermal method consists of three types of processes hydrothermal synthesis, hydrothermal oxidation, and hydrothermal crystallization. Hydrothermal synthesis is used to synthesize mixed oxides from their component oxides or hydroxides. The particles obtained are small, uniform crystallites of 0.3-200 jim in size and dispersed each other. Pressures, temperatures, and mineralizer concentrations control the size and morphology of the particles. In the hydrothermal oxidation method, fme oxide particles can be prepared from metals, alloys, and intermciallic compounds by oxidation with high temperature and pressure solvent, that is, the starting metals are changed into fine oxide powders directly. For example, the solvothermal oxidation of cerium metal in 2-mcthoxycthanol at 473-523 K yields ultrafine ceria particles (ca 2 nm). 

Whenever the system being titrated forms a reversible redox couple with its reaction product, the second electrode used in the generation reaction must be shielded from the bulk of the sample solution. For example, in the titration of iron(II) with anodically generated cerium(TV), the cathode is placed in a separate compartment to prevent the reduction of iron(III). In this example, iron(II) undergoes direct anodic oxidation during the bulk of the titration until the bulk concentration of iron(II) is so low that its rate of mass transfer can no longer sustain the applied current. At this point the intermediate oxidation of cerium(III) permits 100% current efficiency to be maintained to the end point. 

The chemical composition of imported, European-made majolica is different from that of majolica made in Mexico (J). The difiFerences in the concentrations of the oxides of cerium, lanthanum, and thorium are eaily recognized the Spanish majolica contains approximately twice as much of each of these oxides as the Mexican majolica. The mineralogical composition, too, of the pottery products of each area is fundamentally different and can easily be identified. The ceramic types and their origins, based on archaeological arguments, can be found in Table I. 

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