Adsorption reaction, with partial charge

The simulations suggest the following picture for an ion transfer reaction before the reaction the ion is located in a weak adsorption site, where it is separated from the electrode by one layer of water molecules. As the ion approaches the electrode surface it displaces water from the surface and partially looses its solvation shell this requires a substantial energy of activation. Subsequently, the ion moves down the free energy curve towards an adsorption site on the metal surface simultaneously the electronic interaction with the metal increases, electron exchange becomes adiabatic, and the adsorbed particle carries a partial charge (see next section). 

Adsorption of toluene on zeolites Li-X, Na-X, K-X, Rb-X, and Cs-X has been investigated with quantum chemical methods. Calculations of geometries, Mulliken partial charges, and C chemical shift parameters of clusters representing the catalytically active site are presented. The polarisation of the toluene carbons is the first step in alkylation reactions catalysed by zeolites and, at an early stage, will influence the outcome of the reaction. We show the simultaneous influence of the Lewis acidic cation and the basicity of the zeolite is responsible for altering the electron distribution within the toluene and thus affecting the outcome of an alkylation reaction. 

In some electrode reactions it may be appropriate to consider that partial charge transfer occurs. In the case of the underpotential deposition of metals, the electrode process leads to the formation of a monolayer or sub-monolayer of metal atoms which interact with the substrate. In the one extreme, the metal-metal bond may have considerable ionic character, so that the reaction approaches ion adsorption, whereas at the other limit an essentially electroneutral surface atom is formed. These complex electrode processes have been discussed extensively in recent years, and the concept of the electrosorption valency [30] has emerged as a way of describing the nature of the under-potential deposit. 

The voltammetry curve for the Ru(ioio) surface in 0.05 M H2SO4 solution (Fig. 4a) reveals a remarkable difference between the oxidation processes forRu(OOOl) andRu(10l 0). The oxidation of this face is more facile than that of Ru(OOOl), as indicated by the onset of the reaction at lower potentials and by increase of the charge with each potential cycle. This difference most likely is the consequence of the more open structure of the Ru(1010). A pair of peaks at 0.12 and 0.3 V is reminiscent of hydrogen adsorption on Pt metals. However, CO displacement showed a negative charge of -354 pC cm . Thus, the peaks probably represent partial Ru oxidation to RuOH, wherein OH is the predominant adsorbed species, perhaps with some co-adsorption of bisulfate. 

The partial orders with respect to [OH ] observed for most silicate mineral dissolution reactions can be explained by the surface complexation model (Blum and Lasaga, 1988 Brady and Walther, 1989). Brady -and Walther (1989) showed that slope plots of log R vs. pH for quartz and other silicates at 25 °C is not inconsistent with a value of 0.3. Plots of the log of absorbed OH vs. pH also have slopes of about 0.3, suggesting a first-order dependence on negative charge sites created by OH adsorption. Because of the similarity of quartz with other silicates and difference with the dependence of aluminum oxides and hydroxide dissolution on solution [OH ], Brady and Walther (1989) concluded that at pH >8 the precursor site for development of the activated complex in the dissolution of silicates is Si. This conclusion is supported by the evidence that the rates (mol cm s ) at pH 8 are inversely correlated with the site potential for Si (Smyth, 1989). Thus it seems that at basic pH values, silicate dissolution is dependent on the rate of detachment of H3SiO4 from negative charge sites. 

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