Cerium ion

Cerium(IV) oxidizes ferrous ion to ferric and the cerium ions are stable under the conditions of a molten silicate—glass bath. Furthermore, cerium itself has no absorption ia the visible region. Economical additions of cerium, as cerium concentrate, enable the efficient use of raw materials containing trace quantities of iron (26). 

When PAN block copolymers are synthesized with the help of such method the reaction is conducted during a period of time (20—30 min) shorter than the induction period of AN polymerization (45 min) in the presence of cerium ions. When the mechanism and the laws governing the reaction of AN copolymerization with PEO and PPO were studied, it was established that the initiation of the block copolymerization proceeds in accordance with the following scheme ... 

Though the increase of the concentration of Ce4+ ions also increases the yield of copolymer, it facilitates at the same time the decrease of the length of polyacrylonitrile blocks due to cerium ions participating in the disruption of the growing chain. 

M(0H)2SOi, H2O where M=Zr (8), Hf (12) also have been determined and reveal the presence of almost planar zigzag chains of metal atoms joined by double hydroxide bridges. The single exception to this trend toward formation of double hydroxy-bridged metal dimers or chains is the compound which is best described as CeOSOif,H20 (17). However, even in this structure the cerium ions form chains which are linked by bridging oxide ions. 

The oxidation of an anthracene suspension in sulfuric acid conducted in the presence of cerium salts can serve as an example of mediated oxidation. In the bulk solution the Ce" ions chemically oxidize anthracene to anthraquinone. The resulting Ce ions are then reoxided at the anode to Ce". Thus, the net result of the electrochemical reaction is the oxidation of anthracene, even though the electrochemical steps themselves involve only cerium ions, not anthracene. Since the cerium ions are regenerated continuously, a small amount will suffice to oxidize large amounts of anthracene. 

An example of the process of a passivating metal is the reaction of tetravalent cerium with iron (see Fig. 5.54D). Iron that has not been previously passivated dissolves in an acid solution containing tetravalent cerium ions, in an active state at a potential of Emix2. After previous passivation, the rate of corrosion is governed by the corrosion current ya and the potential assumes a value of Emixl. 

The OSC values at 400 and 500°C for the two samples are compared in Table 8.3. At these temperatures, the layer number n involved in the reduction process is significantly higher for the mixed oxide than for ceria. At 500°C, more than three cerium ion layers (i.e. almost two cells) are reduced upon the first pulse of CO. 

Results and Discussion. Of the 12 samples of starch graft copolymer synthesized, half were hydrolyzed to anionic polyelectrolytes. Synthesis data on these 6 samples are given in Table 2. These particular samples were chosen for hydrolysis because the samples can be intercompared to see the effect of synthesis variables on ultimate product properties. Samples 5, 8, and 11 have the same mole ratio of cerium ion to starch backbone, N, in their reaction mixture. Samples 7, 8, and 9 all have the same refctable mass per starch molecule,... 

To introduce a barrier layer when utilizing doped ceria electrolytes (SDC, GDC, or lanthanum-doped ceria, LDC) to prevent the reduction of Ce4+ to Ce3+. Reduction of cerium cations results in unwanted electronic conductivity that lowers fuel efficiency [34], and mechanical degradation that results from the volume expansion of cerium ions upon reduction [35],... 

This reaction appears to be first order because the cerium ions are in excess, so the concentration does not really change. We look at pseudo-order reactions on p. 387. 

For the cerium pz sandwich complex, only data for the analogous porphyrin sandwich is available. For the porphyrin, not only are one ring reduction and two ring oxidations observed, a metal-based Ce(IV)/Ce(III) reduction is observed, at a lower potential than the ring oxidation. The electron-transfer rate constant for the Ce(IV)/Ce(III) process was found to be very slow, 2.2 1.0 X 10 cm 1 because the/orbital of the cerium ion is buried between the two macrocycles making it difficult for the incoming electron to access it. For the Ce IVl pz, a similar Ce(IV/III) reduction is observed, at a lower potential than that observed for the porphyrin. 

Yokoyama, C. and Misono, M. Catalytic reduction of nitrogen oxides by propene in the presence of oxygen over cerium ion-exchanged zeolites II. Mechanistic study of roles of oxygen and doped metals. J. Catal, 1994, Volume 150,9-17. 

A typical chemical system is the oxidative decarboxylation of malonic acid catalyzed by cerium ions and bromine, the so-called Zhabotinsky reaction this reaction in a given domain leads to the evolution of sustained oscillations and chemical waves. Furthermore, these states have been observed in a number of enzyme systems. The simplest case is the reaction catalyzed by the enzyme peroxidase. The reaction kinetics display either steady states, bistability, or oscillations. A more complex system is the ubiquitous process of glycolysis catalyzed by a sequence of coordinated enzyme reactions. In a given domain the process readily exhibits continuous oscillations of chemical concentrations and fluxes, which can be recorded by spectroscopic and electrometric techniques. The source of the periodicity is the enzyme phosphofructokinase, which catalyzes the phosphorylation of fructose-6-phosphate by ATP, resulting in the formation of fructose-1,6 biphosphate and ADP. The overall activity of the octameric enzyme is described by an allosteric model with fructose-6-phosphate, ATP, and AMP as controlling ligands. 

The main processes occurring in this system are the following [219] bromate oxidizes trivalent cerium to tetravalent cerium Ce4+ oxidizes bromomalonic acid, and is reduced to Ce3+. The bromide ion, which inhibits the reaction, is isolated from the oxidation products of bromomalonic acid. During the reaction, the concentration of the Ce4+ ions (and Ce3+) oscillates several times, passing through a maximum and a minimum. The shape of the peaks of concentrations and the frequency depend on the reaction conditions. The autooscillation character of the kinetics of the cerium ions disappears if Ce4+ or Br are continuously introduced with a low rate into the reaction mixture. The autooscillation regime of the reaction takes place only in a certain interval of concentrations of the reactants [malonic... 

A perspective method for the production of HCP was proposed by Labarre et al 92-94) [t invo]ves radical graft-copolymerization of methyl methacrylate onto heparin effected by cerium salts (Ce4+). As well as other hydroxyl-containing polymers, heparin may react with cerium ions producing free radicals which may initiate graft-copolymerization of unsaturated compounds ... 

Several reports describe the mechanism of polymerisations using cerium compounds in combination with alcohols77,78, diols79,80 and polyols81. Only in a limited number of kinetic studies was the concentration of cerium ions measured during the polymerisation reaction. Mohanty et alm, Rout et al.m, Jayakrishnan et al.65 and Gupta and Behani.67 followed the reduction of Ce(IV) ions titrimetrically. 

According to Zhabotinskii, a simplified reaction scheme in the system consisting of malonic acid (MA) + bromate and cerium ions is of the form... 

In presence of 5% H20 and 0,05% S02 in the gas mixture, 15-30% loss of activity is observed at 573 K over Fe-MFI (101). The addition of cerium ions increases the stability towards the presence of H20+S02 (106). Above 573 K Yang et al. (104) reported that H20+S02 have little effect on the activity. According to these authors (104), water and sulfates increase the Bronstcd acidity of the catalysts and consequently the adsorption of ammonia (104). On overexchanged Fe-MFI prepared by sublimation, the presence of water (2.5%) in the gas mixture also promotes the NO conversion. S02 (0.02%) or H20+S02 inhibits the reaction only at temperatures below 650 K (103). On the other hand, upon addition of 8% H20 at 573 K, Ramachandran et al. (83) observe a drop of 40% in the NO conversion over a pelletized Fe-MOR containing an alumina binder. 

CerOx [Cerium Oxidation] An electrochemical process for oxidizing organic materials such as pesticides in wastewater. Cerium ion is an intermediate. This is electrochemically oxidized to Ce4, which is the actual oxidant. 

All reactions, save 10, contained O.SO g of lignin and O.IS ml of cerium ( + 4) ion. Reaction 10 contained 4.39 g of lignin and 1.28 ml of cerium ion. A = 2,2-dimethyl-3-imino-4-oxohex-5-ene-l-sulfonic acid. B = Hydroperoxide. Samples 1-7 Values arc weight of l,4-dioxa-2-hydropcroxycyclohexane in g. Samples 8-22 Values arc amount of aqueous solution of l,2-dioxy-3,3-dimethylbutane in ml. Equivalent/ml = 7.23 x 10". ... 

Eirst balance the iodine, then the copper. The cerium has to provide for four positive charges, so there are four cerium ions on each side.)... 

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