Cerium cation

Depending on the electronegativity and the cation s oxidation state, the oxide can be either acidic or basic. Also, doping the ceria lattice does not automatically mean a substitution of a host cerium cation. Inomata and coworkers showed, in the case of Ce(i x)FexOy, that Fe3+ ions were located not only at Ce4+ sites, but also at interstitial sites (49). These interstitial ions bring about an increased barrier for electrons moving between Ce3+ and Ce4+, and influence the redox potential and the ease of reducibility of the material. 

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],... 

Ce02-based solid solutions exhibit higher ionic conductivity than in YSZ but they are partially reduced in the presence of fuel gas. The oxygen partial pressure domain where the conductivity is purely ionic is very narrow because of the reduction of cerium cations. For example, it extends from 1 to 10-2 at 1000°C for (CeO2)0... 

The first Ce(IV) complex stabilized by an alkoxo functionalized Ai-heterocyclic carbene anion has recently been reported. The complex is made by oxidation of the corresponding trivalent cerium complex using benzoquinone (Figure 8.36). The cerium cation is coordinated by two bidentate ligands and two monodentate ligands, in which the NHC groups are unbound [123],... 

Cation interstitials provide an alternative way to create positively charged defects. These interstitials may be formed by transfer of cerium cations located on the surface to an interstitial position and by the removal of two anions to the gas phase for each cerium interstitial formed. The process can be simply represented in the following equation ... 

A more detailed investigation, including the effect of varying the amount of cation exchange, was undertaken for catalysts containing zinc and cerium cations as they were both active at low temperatures but exhibited different product selectivities. A similar study of the nickel-exchanged zeolite will be reported elsewhere (8). 

Physically, the relationship between catalytic activity and Z f can be understood from a study of single phase bismuth cerium molybdate solid solutions. The results show that maximum activity is achieved when there exists a maximum number and optimal distribution of all the key catalytic components bismuth, molybdenum and cerium in the solid. Therefore, it reasonably follows that the low catalytic activity observed for the two phase compositions where Af Af(min) results from the presence of interfacial regions in the catalysts where the compositional uniformity deviates significantly from the equilibrium distribution of bismuth and cerium cations present in the solid solutions. These compositions may contain areas in the interfacial region which are more bismuth-rich or cerium-rich than the saturated solid solutions. Conversely, at Af(min), the catalyst is similar to an ideal mixture of the two optimal solid solutions. The compositional homogeneity of the interfacial region approaches that of the saturated solid solutions. Therefore, the catalytic behavior of compositions at Af(min) is similar to that of the saturated solid solutions. 

Calculated and experimental values, expressed in pmol-CO.g, are collected in Table 1. The ratio of these two values may represent the number of oxygen layer involved in the redox process. In all cases, the calculated values are lower than the experimental ones. This observation shows that 2 to 3 layers are involved in the redox process. The increase of the OSC along with the amount of Pr shows that the presence of this element induces the creation of anionic vacancies. In fact, in substitution to cerium cations, Pr ions may undergo a redox process (Pr /Pr" ) whereas it is not possible for zirconium cations. 

When water salts solutions are used in OPCM synthesis, provided the Me CA ratio is equal to 1 6 in all the composition range studied here (up to Zr relative content equal to 0.9), single phase samples with a cubic fluorite-like structure are formed. Thus, for ceria-zirconia samples with zirconia content up to 50 mol. %, ceria-based cubic solid solution is formed. For those samples, the lattice parameter is decreased as compared with that of a pure ceria phase, due to cerium cations substitution by zirconium cations with a smaller... 

Pronounced variations with samples composition were also observed in the hydroxyls stretching region (Fig. 2c). For pure ceria sample, low-frequency bands corresponding to bridging hydroxyls bound with three cerium cations ( 3638 cm ) as well as bulk hydrogen bound hydroxyls (band 3570 cm ) dominate. A shoulder at 3698 cm can be assigned to bridging hydroxyls bound with two Ce cations [14]. 

The simultaneous formation of nitrites and hyponitrites can be imderstood on the basis of the redox properties of Ce ions. Thus nitrites may form when NO is adsorbed on Ce " " ions with anion vacancies in their coordination spheres, leading to reduction of the cerium cation ... 

Part of these N2O2" groups may be unstable at 295 K and decompose to produce N2O (that can remain adsorbed or desorbe into the gas phase) and 0 anions close to the reoxidized cerium cations. Since N2O is observed in coincidence with the cis type of N202° species, it seems probable that these latter are mor unstable and reactive than those of the trans kind. The fact that such hyponitrites (and subsequently N2O) can be detected for Tv lower than that necessary to observe... 

Formation of dispersed phase of ceria in the dealuminated mordenites modified with ceria/cerium was registered by XRPD. Decrease in acidity at increased content of ceria may be prescribed to ion-exchange of protons with cerium cations. An extra mesoporous structure of ceria at higher metal loading (more than 10 wt. %) was found. On one side, a lower acidity and narrower channels of catalysts resulted in the lower catalytic activity, on the other side higher selectivity to the desired 4,4 -dialkylated biphenyl was achieved. 

Imamoto and co-workers developed procedure B, which is a one-pot transformation of phosphine oxides into phosphine boranes. The cerium cation plays two roles it coordinates to the phosphoryl group to make the deoxygenation with LiAlH4 possible and it also facilitates the reaction between... 

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