Oxides electrostatic fields

We denote by x the distance from the metal surface, and by n x) and rip x) the concentrations of cation vancancies and positive holes in the oxide. Let and Vp be their mobilities, and and Dp their diffusion coefficients. Let F x) be the electrostatic field in the oxide. J, the flux of cation vacancies (number crossing unit area per second), will be expressed by... 

Considerable support exists for Reaction 18a (35). The application of an electrostatic field during radiolysis of ethylene-nitric oxide (I.P. 9.25 e.v.) mixtures showed no enhancement of the butene yields, consistent with an ionic mechanism. When mixtures of C2D4 and C2H4 are irradiated in the presence of nitric oxide, product butene consists almost entirely of C4H8, C4D4H4, and C4D8—evidence for a molecular association mechanism. 

The intercalated catalysts can often be regarded as biomimetic oxidation catalysts. The intercalation of cationic metal complexes in the interlamellar space of clays often leads to increased catalytic activity and selectivity, due to the limited orientations by which the molecules are forced to accommodate themselves between sheets. The clays have electrostatic fields in their interlayer therefore, the intercalated metal complexes are more positively charged. Such complexes may show different behavior. For example, cationic Rh complexes catalyze the regioselective hydrogenation of carbonyl groups, whereas neutral complexes are not active.149 Cis-Alkenes are hydrogenated preferentially on bipyridyl-Pd(II) acetate intercalated in montmorillonite.150 The same catalyst was also used for the reduction of nitrobenzene.151... 

These external fields can affect the physical properties and reactivity of the molecular systems. Such effects are especially important in ordered crystalline environments such as solid oxides and biological macromolecules [25-28]. These local electrostatic fields play an important role in catalytic functions and in governing the stabilization of many biomolecular systems [29-32]. These environmental effects cause dramatic changes in the reactivity, which can be different from the gas phase. 

Most photo-oxidations that occur via the Frei hybrid type II vOi - type II/ivRH mechanism have been conducted in the absence of solvent, which can shield the substrate from the infrazeolite electrostatic field. The exceptions include the photo-oxidations of easily ionized substrate [50,51] that will react even in solvent slurries [10]. For example, Ramamurthy and co-workers [52] reported that irradiation into the oxygen-CT bands (>350 nm) for a series of 1,1-diaryleth-ylenes, 23, in hexane slurries resulted in the formation of oxidized products via the Frei mechanism (Fig. 19). 

Oxidations initiated by thermally induced electron transfer in an oxygen-CT complex represent the thermal analog of the Frei photo-oxidation and are properly classified as hybrid type IlAOi-type IIaRH oxidations (Fig, 2), Such reactions require either zeolites with high electrostatic fields or substrates with low oxidation potentials. In addition, elevated temperatures are known to promote the thermally initiated electron-transfer step, although the possible intrusion of a classical free-radical initiation chain oxidation at higher temperatures must be considered. 

This model of a complex or of a crystalline salt of a metal ion in a compound such as a halide or oxide is of an electrostatic, point charge, or point dipole type. The ligands or neighbors of the metal ion are treated as structureless, orbital-less point charges, which set up an electrostatic field. The effect of this field on electrons in the d orbitals of the metal ion is then investigated. 

Abstract. An embedded-cluster approximation is adopted for simulating the heterolytic dissociation of hydrogen at two intrinsic defects on the (001) surface of magnesium oxide the isolated anion vacancy, and the tub divacancy. The dissociation process is shown to be critically dependent on the structure of the electrostatic field at the surface both as concerns energetics and final configuration. 

The adsorption of CO and reduction of thin films of CuO was studied by Palmer (24). The activity of CuO powder and precipitated CuO aerosol in the oxidation of CO at temperatures between 200-400°C. was studied by Bessalow and Kobosew (25). The latter substance was obtained by electrical dispersion and precipitation in an electrostatic field. The aerosol formed was 765 times more active than the correspond-... 

The results of a newly proposed model for adsorption at the oxide/water interface are discussed. The modeling approach is similar to other surface complexation schemes, but mass-law equations are corrected for the effect of the electrostatic field. In this respect, this model bridges the gap between those models that emphasize physical interactions. The general applicability of the model is demonstrated with comparisons of calculations and experimental data for adsorption of metal ions, anions, and metal-ligand complexes. Intrinsic ionization and surface complexation constants can be determined with an improved double extrapolation technique. 

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