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Electrosorption isotherms

The model had been substantiated by measuring the potential dependent electrosorption isotherms of all species involved that show that the proto-nated alcaloids are those species that are by far most strongly adsorbed, whereas the acetyl pyridines are least strongly adsorbed, especially at lower pH relative to the electrosynthesis, which is performed at pH 4 to 4.5. The optically inductive reduction of 2- and 4-acetyl pyridine to the optically active carbinols demands the formation of a dense but not too densely packed surface layer of adsorbed protonated alcaloid, which still allows for insertion of the oxo-compound or the ketyl radical, respectively. Performing the reaction with too high alcaloid concentrations leads to compaction on the adsorbate layer, the ketyl radical is squeezed out, and optimal induction is no longer observed. [Pg.167]

Electrosorption isotherms can be derived from those for adsorption of... [Pg.437]

Keeping these caveats in mind, the analysis to establish whether A, G is a function of (say) pH or (t proceeds as follows. The electrosorption isotherm is. quite generally, written as the functionals... [Pg.441]

Comparison of Electrosorption Isotherms for Hydrogen on Palladium and Platinum... [Pg.244]

Sander and Henze [50] have performed ac investigations of the adsorption potential of metal complexes at Hg electrode. Later, Sander etal. [51] have studied electrosorption of chromium - diethylenetriaminepentaacetic acid (DTPA) on mercury in 0.1 M acetate buffer at pH 6.2 using a drop-time method. The changes in the interfacial activity of the Cr(III)-DTPA complex with the bulk concentration obeyed the Frumkin adsorption isotherm. [Pg.969]

An additional unique feature of electrosorption is that the coverage is a function of potential, at constant concentration in solution. Thus, we can discuss two types of isotherms those yielding 0 as a function of C and those describing the dependence of 0 on E. This is not a result of faradaic charge transfer. Neither is it due to electrostatic interactions of the adsorbed species with the field inside Ihc compact part of the double layer, since a potential dependence is observed even for neutral organic species having no permanent dipole moment. As we shall see, it turns out that the potential dependence of 0 is due to the dependence of the free energy of adsorption of water molecules on potential. [Pg.477]

An isotherm describing electrosorption can be written in general form as ... [Pg.487]

Fig. IIJ Langmuir isotherm for the electrosorption of a large neutral species, each adsorbate molecule replacing n water molecules from the surface. Fig. IIJ Langmuir isotherm for the electrosorption of a large neutral species, each adsorbate molecule replacing n water molecules from the surface.
Systematic electrosorption studies are not abundant in the literature in that rarely are salt effect simultaneously measured over a large range. What are available are Just millions of adsorption Isotherms under a number of conditions, sometimes in connection with electrokinetlc and/or stability studies. However useful such studies may be, they do not provide enough information to carry out analyses as Intended in the present section. We shall therefore Illustrate the subject matter with two case studies, choosing silver Iodide and oxides as the, rather representative, examples. [Pg.442]

Both thin-layer techniques were developed by Schmidt, Siegenthaler et al. [3.55, 3.67, 3.68] and allow an independent and precise measurement of q(E,p) and iXE.fi) isotherms. From the q-T plot, the electrosorption valency can be directly determined as illustrated in Fig. 3.12 [3.97, 3.105]. The electrosorption valency was found to be Y = z m both UPD systems indicating the absence of cosorption and competitive sorption processes in the systems studied. [Pg.59]

Indeed, in situ STM imaging with lateral atomic resolution of a flame-annealed Au(lOO) substrate in deaerated perchloric or sulphuric acid solutions fi ee of Ag ions shows the existence of a potential-induced surface reconstruction with an undulated quasi-hexagonal ( quasi-hex ) structure at Ew < 240 mV (cf. Figs. 2.5 and 2.7). Reconstructed domains were not observed at higher hE, which indicates that the quasi-hex reconstruction of the Au(lOO) surface is lifted by the applied positive electrode potential. In deaerated perchloric or sulphuric acid solutions containing Ag ions, Ag UPD is clearly indicated in cyclic voltammograms (Fig. 3.20a) as well as in q E) or r E) isotherms at = constant in the underpotential range 0 mV < A < 600 mV (Fig. 3.20b). Electrosorption valency measurements under ITL... [Pg.77]

This UPD system is characterized by a significant positive Me-S lattice misfit (do.Tl = 0.3400 nm, doAg - 0.2890 nm) and by the formation of two T1 monolayers in the UPD range. Cyclic voltammograms and l E) isotherms of the system Ag(M/)/Pb, H, CIO4, measured with the FTTL technique [3.105], are presented in Figs. 3.3 and 3.10, respectively. The electrosorption valency was found to be = z = 1 in the entire UPD range (Fig. 3.12b). This means that cosorption or competitive adsorption processes of anions can be excluded in this system. [Pg.94]

The preceding sections pertain to equilibrium conditions of electrosorption of a reactant which adsorbs without a simultaneous charge transfer. Under the latter conditions, or in the case of intermediates of an electrode reaction adsorbed on the electrode, adsorption isotherms contain additional potential dependent terms. [Pg.379]

At equilibrium, or in quasi-equilibrium, the coverage with A will depend on the type of the isotherm involved and on potential. The form of the dependence on potential will also depend on the type of the isotherm involved. Two cases are most often encountered—electrosorption occurring under Langmuir or Temkin conditions. In the former case [Eq. (94)]... [Pg.379]

Other mechanisms studied include electrosorption with Langmuir isotherm [641] and a Volmer-Heyrovsky type of mechanism [641, 642], The reader should consult these references for more details. [Pg.328]

A recent study " of the electrosorption of ethylene on Pt electrodes from 1 N sulfuric acid showed that a limiting coverage of 0 == 0.4 was reached when the concentration of ethylene in solution exceeded 10" moles/liter. The adsorption isotherm obtained at 30°C and a potential of 0.4 V (N.H.E.) is shown in Figure 8. The variation of partial coverage at extreme values of the potential was interpreted in terms of a competition with water model proposed by Bockris et The low value of... [Pg.92]

Further experiments need be done to clarify this point. One may surmise perhaps that the Langmuir adsorption isotherm applies for electrosorption of formic acid (as is the case of, e.g., ethylene " ) and the discrepancy between reported values of the reaction order arises due to the gradual change from the linear 6-c relationship observed at low values of the coverage to an approximate Freundlich-like region at intermediate-coverage... [Pg.112]


See other pages where Electrosorption isotherms is mentioned: [Pg.19]    [Pg.437]    [Pg.438]    [Pg.441]    [Pg.295]    [Pg.296]    [Pg.296]    [Pg.297]    [Pg.15]    [Pg.99]    [Pg.93]    [Pg.19]    [Pg.437]    [Pg.438]    [Pg.441]    [Pg.295]    [Pg.296]    [Pg.296]    [Pg.297]    [Pg.15]    [Pg.99]    [Pg.93]    [Pg.970]    [Pg.15]    [Pg.244]    [Pg.179]    [Pg.50]    [Pg.299]    [Pg.62]    [Pg.126]    [Pg.970]    [Pg.372]    [Pg.374]    [Pg.374]    [Pg.366]    [Pg.387]    [Pg.112]    [Pg.354]    [Pg.375]    [Pg.4590]    [Pg.15]   
See also in sourсe #XX -- [ Pg.244 ]

See also in sourсe #XX -- [ Pg.296 ]




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Electrosorption

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