Redox properties of cerium

More recently, infrared studies on the adsorption of NO and the coadsorption of NO and O2 onto Ce,Na-mordenite zeolite indicate that the redox properties of cerium (Ce3+/Ce4+) may contribute to the easier desorption of oxidized NO species (Ito et al. I995a,b, 1996). In this way, the formation of NO+ is associated with zeolite acid sites, and NO3 species associated to La cations, both NO+ and NO were found to desorb more easily from Ce,Na-mordenite than from La,Na-mordenite (Ito et al. 1995a). 

Cerium(IV) oxide-based heterogeneous catalysts are of interest in oxidation owing to the unique redox properties of cerium, i.e., if the crystallite size of ceria decreases, an increase in the oxygen vacancy defect concentration occurs leading to attractive catalytic properties.On the other hand, due to peculiar catalytic activity of gold, its combination with other materials is also appealing, especially when the combination promotes the... 

R G. Harrison, I. K. Ball, W. Azelee, W. Daniell, and D. Goldfarb, Nature and surface redox properties of copper(ll)-promoted cerium(lV) oxide CO oxidation catalysts, Chem. Mater. 12, 3715-3725 (2000). 

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 ... 

Most kinetic determinations of anions involve the iodide ion, which exhibits a strong catalytic effect on the reaction between cerium(IV) and arsenic(III) and a few others as a result of the redox properties of the I2/ I couple. Other anions that can be determined using their intrinsic catalytic effect include sulfur-containing species such as sulfite, sulfide, and thiosulfate, which are quantified by means of the iodine/sodium azide system, and phosphates, which are measured through their effect on the formation of molybdenum blue. Table 5 gives illustrative examples of determinations for these anions and a few others. 

Rynkowski, J.M., Szynkowska, M.I., Paryjczak, T., and Lewiscki, A. Redox properties of AI2O3-supported cerium oxides. Chem. Environ. Res. 1999, 8, 261-270. 

Cerium is the most abundant element of the rare earths. On average the Earth s crast contains 66 ppm of cerium (=66 g per ton), a value that is very comparable with the abundance of copper (68 ppm) (Emsley, 1991). Eew people know that there are on Earth larger resources of cerium than of other more popular elements like cobalt (29 ppm), lead (13 ppm), tin (2.1 ppm), silver (0.08 ppm) or gold (0.004 ppm). A special property of cerium is that it has a stable tetravalent oxidation state besides the trivalent state which is so common for the rare earths. Although the tetravalent oxidation state is also known for solid state compounds of praseodymium and terbium, cerium is the only rare-earth element that has a stable tetravalent oxidation state in solution. Many of the applications of cerium are based on the one-electron Ce +/Ce + redox couple. 

Sardar, K., Playford, H.Y., Darton, R.J., Barney, E.R., Hannon, A.C., Tompsett, D., Fisher, J., Kashtiban, R.J., Sloan, J., Ramos, S., Cibin, G. and Walton, R.I. (2010) Nanocrystalline cerium-bismuth oxides synthesis, structural characterization, and redox properties. Chemistry of Materials, 22 6191-6201. 

The main usefulness of Eh-pH diagrams consists in the immediacy of qualitative information about the effects of redox and acid-base properties of the system on elemental solubility. Concerning, for instance, cerium, figure 8.20 immediately shows that, within the stability field of water, delimited upward by oxidation boundary curve o and downward by reduction boundary curve r, the element (in the absence of other anionic ligands besides OH groups) is present in solution mainly as trivalent cerium Ce and as soluble tetravalent hydroxide Ce(OH)2. It is also evident that, with increasing pH, cerium precipitates as trivalent hydroxide Ce(OH)3. 

In order to improve the resistance of Ni/Al203-based catalysts to sintering and coke formation, some workers have proposed the use of cerium compounds [36]. Ceria, a stable fluorite-type oxide, has been studied for various reactions due to its redox properties [37]. Zhu and Flytzani-Stephanopoulos [38] studied Ni/ceria catalysts for the POX of methane, finding that the presence of ceria, coupled with a high nickel dispersion, allows more stability and resistance to coke deposition. The synergistic effect of the highly dispersed nickel/ceria system is attributed to the facile transfer of oxygen from ceria to the nickel interface with oxidation of any carbon species produced from methane dissociation on nickel. 

Unstabilized chrome yellow pigments have poor lightfastness, and darken due to redox reactions. Recent developments have led to improvements in the fastness properties of chrome yellow pigments, especially toward sulfur dioxide and temperature. This has been achieved by coating the pigment particles with compounds of titanium, cerium, aluminum, antimony, and silicon [3.134] — [3.142]. 

Cerium(lV) compounds with suitable reducing agents, readily initiate the redox polymerization of, for example, vinyl monomers [22]. This property is used to initiate graft polymerization of vinyl monomers onto cellulose, wool, starch, cotton, etc. in order to, e.g. improve mechanical strength, resist moisture penetration and reduce micro-organism attack. 

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