Cerium effect

DeganeUo F, Liotta LF, Longo A, Casaletto MP, Scopelletti M. Cerium effect on the phase stmeture, phase stability and redox properties fo ce-doped strontium ferrates. Solid State Chem. 2006 179 3406. 

Ste] Stepanova, M.V, Fedorov, V.N., Sliozberg, S.K., Bakirov, Zh.T., Cerium Effect on Some Properties of the Cu-Ni-P and Cu-Fe-P Alloys (in Russian), Izv. Vyss. Uchebn. Zaved., Uvetn. MetalL, (4), 77-79 (1979) (Morphology, Experimental, Electr. Prop., Interface Phenomena, Meehan. Prop., 6)... 

In general the lanthanides, including cerium, have a low toxicity rating (17), especially when they are present in material having low aqueous solubiUty. When orally adrninistered poor absorption from the gastrointestinal tract tends to result in the lanthanides generally having Httle effect. The anion is often an important deterrninant in toxicity. 

Cobalt in Driers for Paints, Inks, and Varnishes. The cobalt soaps, eg, the oleate, naphthenate, resinate, Hnoleate, ethyUiexanoate, synthetic tertiary neodecanoate, and tall oils, are used to accelerate the natural drying process of unsaturated oils such as linseed oil and soybean oil. These oils are esters of unsaturated fatty acids and contain acids such as oleic, linoleic, and eleostearic. On exposure to air for several days a film of the acids convert from Hquid to soHd form by oxidative polymeri2ation. The incorporation of oil-soluble cobalt salts effects this drying process in hours instead of days. Soaps of manganese, lead, cerium, and vanadium are also used as driers, but none are as effective as cobalt (see Drying). 

In an actual exhaust system controlled by the signal of the oxygen sensor, stoichiometry is never maintained, rather, it cycles periodically rich and lean one to three times per second, ie, one-half of the time there is too much oxygen and one-half of the time there is too Httle. Incorporation of cerium oxide or other oxygen storage components solves this problem. The ceria adsorbs O2 that would otherwise escape during the lean half cycle, and during the rich half cycle the CO reacts with the adsorbed O2 (32,44,59—63). The TWC catalyst effectiveness is dependent on the use of Rh to reduce NO and... 

However, solubility, depending as it does on the rather small difference between solvation energy and lattice energy (both large quantities which themselves increase as cation size decreases) and on entropy effects, cannot be simply related to cation radius. No consistent trends are apparent in aqueous, or for that matter nonaqueous, solutions but an empirical distinction can often be made between the lighter cerium lanthanides and the heavier yttrium lanthanides. Thus oxalates, double sulfates and double nitrates of the former are rather less soluble and basic nitrates more soluble than those of the latter. The differences are by no means sharp, but classical separation procedures depended on them. 

During the addition of the cerium(IV) solution up to the equivalence point, its only effect will be to oxidise the iron(II) (since K is large) and consequently change the ratio [Fe3+]/[Fe2 + ], When lOmL of the oxidising agent have been added, [Fe3+]/[Fe2 + ] = 10/90 (approx.) and... 

The standardisation of thiosulphate solutions may be effected with potassium iodate, potassium dichromate, copper and iodine as primary standards, or with potassium permanganate or cerium)IV) sulphate as secondary standards. Owing to the volatility of iodine and the difficulty of preparation of perfectly pure iodine, this method is not a suitable one for beginners. If, however, a standard solution of iodine (see Sections 10.112 and 10.113) is available, this maybe used for the standardisation of thiosulphate solutions. 

With the exception of iron(II) and uranium(IV), the reduced solutions are extremely unstable and readily re-oxidise upon exposure to air. They are best stabilised in a five-fold excess of a solution of 150g of ammonium iron(III) sulphate and 150 mL of concentrated sulphuric acid per litre [approximately 0.3M with respect to iron] contained in the filter flask. The iron(II) formed is then titrated with a standard solution of a suitable oxidising agent. Titanium and chromium are completely oxidised and produce an equivalent amount of iron(II) sulphate molybdenum is re-oxidised to the Mo(V) (red) stage, which is fairly stable in air, and complete oxidation is effected by the permanganate, but the net result is the same, viz. Mo(III)- Mo(VI) vanadium is re-oxidised to the V(IV), condition, which is stable in air, and the final oxidation is completed by slow titration with potassium permanganate solution or with cerium(IV) sulphate solution. 

A detailed study of the dehydrogenation of 10.1 l-dihydro-5//-benz[6,/]azcpinc (47) over metal oxides at 550 C revealed that cobalt(II) oxide, iron(III) oxide and manganese(III) oxide are effective catalysts (yields 30-40%), but formation of 5//-dibenz[7),/]azepinc (48) is accompanied by ring contraction of the dihydro compound to 9-methylacridine and acridine in 3-20 % yield.111 In contrast, tin(IV) oxide, zinc(II) oxide. chromium(III) oxide, cerium(IV) oxide and magnesium oxide arc less-effective catalysts (7-14% yield) but provide pure 5H-dibenz[b,/]azepine. On the basis of these results, optimum conditions (83 88% selectivity 94-98 % yield) for the formation of the dibenzazepine are proposed which employ a K2CO,/ Mn203/Sn02/Mg0 catalyst (1 7 3 10) at 550 C. 

Aravamudan and Venkappayya75 oxidized dimethyl sulphoxide in acetate buffer of pH 4 to 4.5 and with a reaction time of only 1 min. They then added potassium iodide and acid and titrated with thiosulphate the iodine liberated by unused reagent. They reported that cerium(IV) and Cr(VI) were much less effective oxidizing reagents for the sulphoxide. A very similar procedure was used by Rangaswama and Mahadevappa76 to determine dimethyl sulphoxide and numerous other compounds with chloramine B. 

The crystal structures of Hf 2 (OH) 2 (S0O 3 (H2O) i, (14) and Ce2(0H)2(S0i,)3 (H20)it (14) also have been determined and found to be isomorphous to the zirconium compound. The cell constants for this series of four isomorphous compounds reflect the effect of the ionic radii on the dimensions of the unit cell. The values for these cell constants are in Table II. Thus, the cell constants for the zirconium and hafnium compounds are nearly identical and smaller than the cell constants for the cerium and plutonium compounds which are also nearly identical. This trend is exactly that followed by the ionic radii of these elements. 

It was also found [8] that the sintering conditions have significant effects on the resistivity of the Smo.iCeo.gOi.g material. As shown in Fig. 4, the overall resistivity decreases with lower sintering temperature and attains a minimum at the sintering temperature of 1100-1200 °C, which is about 31 ohm-cm at 700 °C measurement. This makes the Smo.2Ceo.801,9 material capable of working as SOFC s electrolyte at temperatures lower than 700 C to avoid possible reduction of cerium (4+) and thus suitable for intermediate-temperature SOFC. 

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. 

The induced reduction of chlorate can be inhibited by iodide, bromide and chloride ions. The effectiveness of these ions is about 400 10 1 in the given order. The order and the magnitude of the effect agree fairly well with the catalytic activity of these ions in the arsenic(III)-cerium(IV) reaction. This inhibition by halides is presumably connected with the opening of a new two-electron route for the arsenic(III)-cerium(IV) reaction. 

However, this method of oxidation differs considerably from the effect of strong oxidizing ions such as cerium(lV), manganic(ril) etc., because these merely gain electrons from the reducing partner. 

Returning to the explanation of induced reactions, we can say the following. Friend s proposal , according to which the error in the H2O2 determination is caused by reaction (83) catalyzed by manganese(II) or cerium(III) formed in the primary reaction between hydrogen peroxide and permanganate or cerium(IV) cannot be accepted. The reaction between the ions mentioned and peroxydisulphate at room temperature is very slow, and, furthermore, the increase in acidity —in contrast to its effect on the induced reaction —promotes the oxidation. There is... 

The effect on the induced reaction of the acidity cannot be satisfactorily considered with the kinetic data available. It was mentioned that the rate of reaction between hydrogen peroxide and peroxydisulphate is at maximum at about pH 5. In contrast, the value of Fj obtained cerimetrically goes through a flat maximum in the pH range from 1-2. This maximum should be regarded as an apparent one because the hydrolysis of cerium(IV) is considerable at pH s higher... 

One of the most promising processes is the active DeNO based on NO -trap materials. It has been developed for lean-burn gasoline engines. Cerium compounds are thought to intervene in different steps of the whole process (1) NO oxidation, (2) NO storage, (3) Nitrate desorption and NO reduction. Most probably, the main role of OSC materials is to accelerate HC partial oxidation during rich-spikes (giving CO and H2 as NO reducers). However, this beneficial effect of OSC compounds competes with a detrimental reaction,... 

Oh, S.H. (1990) Effects of cerium addition on the CO-NO reaction kinetics over alumina-supported rhodium catalysts, J. Catal. 124, 477. 

---