Infrared , redox properties

To finish with another trend for NO removal consisting in NO direct decomposition, we would like to depict the infrared study of NO adsorption and decomposition over basic lanthanum oxide La203 [78], In this case, the basic oxygens are proposed to lead to N02 and N03 spectator species, whereas the active sites for effective NO decomposition are described as anion vacancies, which are often present in transition metal oxides. This last work makes the transition with the study of DeNO, catalysts from the point of view of their ability to transfer electrons, i.e. their redox properties. 

The covalent chemistry of fullerenes has developed very rapidly in the past decade in an effort to modify fuUerene properties for a number of applications such as photovoltaic cells, infrared detectors, optical limiting devices, chemical gas sensors, three-dimensional electroactive polymers, and molecular wires [8, 25, 26, 80-82]. Systematic studies of the redox properties of Cgo derivatives have played a crucial role in the characterization of their unique electronic properties, which lie at the center of these potential applications. Furthermore, electrochemical techniques have been used to synthesize and separate new fullerene derivatives and their isomers as well as to prepare fullerene containing thin films and polymers. In this section, to facilitate discussion of their redox properties, Cgo derivatives have been classified in three groups on the basis of the type of attachment of the addend to the fullerene. In group one, the addends are attached via single bonds to the Cgo surface as shown in Fig. 6(a) and are referred to as singly bonded functionalized derivatives. The group includes... 

Roseboom W, de Lacey AL, Fernandez VM, Hatchikian C, Albracht SPJ. The active site of the [FeFe]-hydrogenase from Desulfovibrio desulfuricans. II. Redox properties, light sensitivity and CO-ligand exchange as observed via infrared spectroscopy. J Biol Inorg Chem. 2006 11(1) 102—18. 

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). 

Structural models, which are synthesized to imitate features of the proposed structure of the active site. These may be used to demonstrate the chemical conditions, which allow such structures to exist, to investigate their chemical properties and to give a better understanding of the spectroscopic characteristics of the native proteins. Examples of these include the mixed carbonyl/cyano complexes of iron, used to verify the infrared spectra to the hydrogenases (Fig 7.4) (Lai et al. 1998) and the nickel-thiolate complexes which have low redox potentials like the hydrogenases (Franolic et al. 1992). 

In certain solids such as titanium dioxide or cadmium sulfide, the energy of the band gap corresponds to that of light (visible, ultraviolet, or infrared), with the result that the solid, when illuminated, may become electrically conducting or acquire potent chemical redox characteristics because of the promotion of electrons to the conduction band (which is normally unoccupied). These properties have obvious practical significance and are considered at length in Chapter 19. 

The electronic interaction between the two metal centers leads to the appearance of IT bands which can be observed in a region ranging from the ultraviolet to the near infrared part of the spectrum. Optical T transitions ace due to electron transfer from one metal center M to the other M. The energy of the IT transition strongly depends on the redox asyirmetry of the metal centers as well as the dielectric properties of the solvent. The general behavior of mixed-valence corrpounds has been reviewed excellently very recently (20). 

Polymerization. Terpolymers of PMVE and TFE with either of the monomers containing a phenoxy group have been prepared in a pressure vessel using an aqueous redox polymerization system. The compositional molar TFE/PMVE ratio in the preferred polymer is about 60/40. The third monomer polymerizes at about the same rate as the PMVE and is fed either neat (as a liquid) or in Freon F-113 solution. Infrared analysis of the band at 10.0/a indicates 75-85% incorporation of the phenoxy compound over the 1-4 mole % monomer change range. One to 2 mole % of the crosslink monomer must be incorporated in the elastomer to ensure good vulcanizate properties. 

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