Cerium sulfate, oxidation with

Alternative cerium salt oxidants with limited suitability have been discussed. Whereas cerium-IV sulfate Ce(S04)2 resulted in reasonable conductivities, but Ce-contaminated PEDOT, (NH4)2Ce(N03)6 yielded PEDOT with only low conductivity. So cerium-based oxidants do not represent advantages compared to iron-III. 

Cerium(IV) sulfate is prepared by heating cerium(IV) oxide, Ce02 with con-... 

Europeum generally is produced from two common rare earth minerals monazite, a rare earth-thorium orthophosphate, and bastnasite, a rare earth fluocarbonate. The ores are crushed and subjected to flotation. They are opened by sulfuric acid. Reaction with concentrated sulfuric acid at a temperature between 130 to 170°C converts thorium and the rare earths to their hydrous sulfates. The reaction is exothermic which raises the temperature to 250°C. The product sulfates are treated with cold water which dissolves the thorium and rare earth sulfates. The solution is then treated with sodium sulfate which precipitates rare earth elements by forming rare earth-sodium double salts. The precipitate is heated with sodium hydroxide to obtain rare earth hydrated oxides. Upon heating and drying, cerium hydrated oxide oxidizes to tetravalent ceric(lV) hydroxide. When the hydrated oxides are treated with hydrochloric acid or nitric acid, aU but Ce4+ salt dissolves in the acid. The insoluble Ce4+ salt is removed. 

Acid soluble rare earth salt solution after the removal of cerium may be subjected to ion exchange, fractional crystalhzation or solvent extraction processes to separate individual rare earths. Europium is obtained commercially from rare earths mixture by the McCoy process. Solution containing Eu3+ is treated with Zn in the presence of barium and sulfate ions. The triva-lent europium is reduced to divalent state whereby it coprecipitates as europium sulfate, EuS04 with isomorphous barium sulfate, BaS04. Mixed europium(ll) barium sulfate is treated with nitric acid or hydrogen peroxide to oxidize Eu(ll) to Eu(lll) salt which is soluble. This separates Eu3+ from barium. The process is repeated several times to concentrate and upgrade europium content to about 50% of the total rare earth oxides in the mixture. Treatment with concentrated hydrochloric acid precipitates europium(ll) chloride dihydrate, EuCb 2H2O with a yield over 99%. 

It is of interest to compare the influence of cerium(III) on the cerium(IV)-ar-Cr(OH2)2(0204)2" reaction with the similar retarding action by cerium(III) which Tong and King (43) found in their careful kinetic investigation of the cerium(IV) oxidation of Cr(OH2)6+3 in acidic-sulfate media. The observed rate law for the latter reaction may be written in the form... 

Gasolines contain a small amount of sulfur which is emitted with the exhaust gas mainly as sulfur dioxide. On passing through the catalyst, the sulfur dioxide in exhaust gas is partially converted to sulfur trioxide which may react with the water vapor to form sulfuric acid (1,2) or with the support oxide to form aluminum sulfate and cerium sulfate (3-6). However, sulfur storage can also occur by the direct interaction of SO2 with both alumina and ceria (4,7). Studies of the oxidation of SO2 over supported noble metal catalysts indicate that Pt catalytically oxidizes more SO2 to SO3 than Rh (8,9) and that this reaction diminishes with increasing Rh content for Pt-Rh catalysts (10). Moreover, it was shown that heating platinum and rhodium catalysts in a SO2 and O2 mixture produces sulfate on the metals (11). 

It is interesting to consider which factors are important in the formation of cerium sulfates. The presence or absence of Pt had little effect, showing that ceria is able to oxidize SO2 without an additional catalyst [42]. Furthermore, the oxidation of SO2 to S04 occurs on ceria to some extent without the addition of gas-phase O. obviously with the simultaneous reduction of ceria [40]. Finally, bulk sulfates were only formed when the ceria samples were exposed to SO2 at temperatures above 250"C. 

Considerable interest has been shown in analytical methods for the determination of algin (68, 72, 78, 101, 158, 171, 21A, 292). Improvements were made in the Lefevre-Tollens hydrochloric acid decarboxylation method by McCready, Swenson, and Maclay (135, 143) to make it more adaptable to routine determinations. Kenyon and coworkers (148, 262, 271, 272) in a series of articles compared various methods for the determination of the carboxyl content of sugar acids. These included the calcium acetate-acetic acid method, the potentiometric titration method in the presence of sodium bromide, decarboxylation and determination of the isolated furfural. Percival and Ross (70, 187) described improvements in the colorimetric carbazole determination of algin. New analytical methods include the oxidation of algin with cerium sulfate (W) and Perlin s (188) recent report of the quantitative thermal decomposition of algin at 255 C. 

Sulfur oxides and nitrogen oxides may be removed from combustion gases by various processes. One of the cost-effective and efficient methods involve dry scrubbing of SOx and NOx over lanthanide-oxygen-sulfur compounds (Jalan and Desai 1992). Cerium sulfate is found to be an effective catalyst toward the reduction of NOx by ammonia. A combined removal of NOx and SOx has been achieved using cerium oxide doped with strontium oxide, lanthanum oxide, calcium oxide, or cerium sulfate. 

The oxides, (R.E.)203, are readily soluble in acids unless they have been ignited at high temperatures, in which case they dissolve more slowly. However, cerium(IAr) oxide dissolves in acids exceedingly slowly. It may be converted to the anhydrous sulfate by heating with concentrated sulfuric acid or may be reduced to cerium (III), and thus rendered soluble, by means of hydrogen peroxide or alkali metal iodide in acidic solution. 

Colorimetric methods are used for the determination of lactic and tartaric acids in wines. In the determination of lactic acid the procedure consists of the conversion of lactic acid into acetaldehyde by heating in the presence of sulfuric acid or by oxidation with cerium(IV) sulfate and subsequent formation of a colored compound with p-hydroxydiphenyl or piperidine and sodium nitroprusside. The red color formed is measured at 560-570nm. 

Phenols (e.g., phenol itself [CeHs-OH or Ar-OH], Table 6.10, item 2) and their esters (e.g., the trifluoroacetate ester of phenol [C6H5-O2CCF3 or Ar02CCH3], Table 6.10, item 3) have been oxidized with air and oxygen (O2), in neutral and alkaUne solutions, with and without ionic and/or radical catalysts and/or irradiation and in a variety of solvents. Enzymes (this chapter and Chapter 12) from a wide variety of sources have also been used. Frequently, oxidation of aromatic systems to phenols cannot be stopped before quinones and products of ring fragmentation occur and numerous, sometimes ill-defined, products result. Thus, as shown in Equation 6.80, oxidation of the polynuclear hydrocarbon chrysene with anunonium cerium(IV) sulfate [ceric ammonium sulfate, Ce(NH,)4(S04)4] is reported to produce 6H-benzo[d]naphtho[l,2-/>]pyran-6-one (8% yield) and a quinone (23% yield). The remainder of the product(s) (69%) was unidentified. 

A study of the cerium(IV) oxidation of hydroquinone and hydroquin-one esters has been undertaken to investigate coupling of phosphorylation to two-electron oxidation. Reactions of substituted hydroquinones are thought to be inner sphere since there is little rate variation with structure (Table 3.2), and Marcus predictions lead to lower estimates of the rate. Although slower than other hydroquinones, the phosphate and sulfate esters show little difference in reactivity, implying that little P-O or S-0 stretching is required to obtain the semiquinone radical. 

Polycyclic ketones undergo Baeyer-VilUger oxidation with ammonium hexanitratocerate(IV) or cerium(IV) ammonium sulfate to afford lactones (Soucy et al., 1972 Mehta et al., 1976). The Baeyer-Villiger oxidation of adamantanone to the corresponding lactone is shown above in scheme 14. Camphorquinone is oxidized to a complex mixture of oxidation products (Danieli and Palmisano, 1976). Simple aliphatic ketones are not oxidized by cerium(IV) in the absence of a catalyst. In presence of ruthenium(III) chloride, cerium(IV) sulfate oxidizes 2-butanonone to acetic acid and formic acid, and 3-pentanone to a mixture of propionic acid, acetic acid and formic acid (Singh et al., 1980). 

The other sulfate hydrates, viz. the nona- and pentahydrate series, behave in a similar way, with a slight difference in the dehydration mechanism. Ce2(S04)3 8H2O and other cerium sulfate hydrates differ by decomposing from the anhydrous sulfate directly to oxide CeOj without step (3). Likewise, 802(804)3 5H2O decomposes without the oxosulfate intermediate (Komissarova et d., 1965b). 

Decarboxylation with hot acid and determination of the carbon dioxide formed is one of the important methods used in the determination of poly-mannuronic adds . Percival and Ross described improv ents in the application of the carbazole method to algin. Recently proposed analytical methods include oxidation with cerium sulfate , and quantitative thermal decomposition at 255 . 

Potassium permanganate oxidizes succinic acid to a mixture of malic and tartaric acid [133-37-9]. 3-Hydroxypropionic acid [503-66-2] is obtained with sodium perchlorate. Cerium(IV) sulfate in sulfuric acid medium oxidizes succinic acid to oxaloacetic acid (71). 

Miscellaneous Compounds. Among simple ionic salts cerium(III) acetate [17829-82-2] as commercially prepared, has lV2 H2O, has a moderate (- 100 g/L) aqueous solubiUty that decreases with increased temperature, and is an attractive precursor to the oxide. Cerous sulfate [13454-94-9] can be made in a wide range of hydrated forms and has solubiUty behavior comparable to that of the acetate. Many double sulfates having alkaU metal and/or ammonium cations, and varying degrees of aqueous solubiUty are known. Cerium(III) phosphate [13454-71 -2] being equivalent to mona2ite, is very stable. 

The ESR spectrum of the pyridazine radical anion, generated by the action of sodium or potassium, has been reported, and oxidation of 6-hydroxypyridazin-3(2//)-one with cerium(IV) sulfate in sulfuric acid results in an intense ESR spectrum (79TL2821). The self-diffusion coefficient and activation energy, the half-wave potential (-2.16 eV) magnetic susceptibility and room temperature fluorescence in-solution (Amax = 23 800cm life time 2.6 X 10 s) are reported. 

In a theoretical study, Lowell et al. W selected oxides from thermodynamic considerations for a process in which SO2 was adsorbed at temperatures greater than 100 C and desorbed by decomposition of the sulfate or sulfite formed, at temperatures below 750 C. Under these constraints, all of 47 oxides considered had potential for adsorption but only 16 had low enough decomposition temperatures to make a process economical. Intuitively, sulfate decomposition temperature should correlate loosely with reducibility of sulfates, so it is interesting that many of the 16 oxides chosen by Lowell, which included cerium and aluminum, have been shown to be useful in the UltraCat process. 

Gadolinium is produced from both its ores, monazite and bastnasite. After the initial steps of crushing and beneficiation, rare earths in the form of oxides are attacked by sulfuric or hydrochloric acid. Insoluble rare earth oxides are converted into soluble sulfates or chlorides. When produced from monazite sand, the mixture of sand and sulfuric acid is initially heated at 150°C in cast iron vessels. Exothermic reaction sustains the temperature at about 200 to 250°C. The reaction mixture is cooled and treated with cold water to dissolve rare earth sulfates. The solution is then treated with sodium pyrophosphate to precipitate thorium. Cerium is removed next. Treatment with caustic soda solution fohowed by air drying converts the metal to cerium(lV) hydroxide. Treatment with hydrochloric or nitric acid sol-... 

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