Coordination adsorption parameter

For bimetallic catalysts, in the equation of the model the denominator containing the coordination (adsorption) parameter is introduced, which shows a more pronounced impact of the coordination (adsorption) processes on DHL hydrogenation compared to the monometallic one. On the other hand, because the coordination (adsorption) parameter Q is very small for PdPt and PdZn nanoparticulate catalysts, the second component in the denominator can be omitted so the equation becomes W=k, i.e., identical to that found for Pd nanoparticles. Among all the catalysts, PdAu stands apart its model equation contains a squared term in the denominator [44], reveaUng the high impact of the substrate/product coordination (adsorption). 

Different supramoleciflar bi- and tetranuclear Pd(II) and Pt(II) complexes of square- or rhomb-hke shape were deposited under potential control from aqueous electrolyte on a Cu(lOO) electrode surface, which was precovered by tetragonal pattern of chloride anions (Fig. 13) [116,151,245]. Although, partial decomposition was observed, it could be concluded that contact with the surface does not affect the metal coordination algorithms, but actively steers the adsorption parameters (relative orientation, internal conformations, etc.)... 

Por the computation we have used the integral method using cubic spline and the combined gradient method of Levenberg-Marquardt [57, 58]. The kinetic models chosen describe well the hydrogenation kinetics. In the formulas presented in Table 3.1 k is the kinetic parameter of the reaction and Q takes into account the coordination (adsorption) of the product (LN) and substrate (DHL) with the catalyst (the ratio of the adsorption-desoprtion equilibrium constants for LN and DHL). Parameters of the Arrhenius equation, apparent activation energy kj mol , and frequency factor k, have been determined from the data on activities at different temperatures. The frequency factor is derived from the ordinate intercept of the Arrhenius dependence and provides a measure of the number of collisions or active centers on the surface of catalytic nanoparticles. 

Then, the parameter identification method was extended to calibration method. For calibration, which coordinate to calculate parameter is very important. The ideal coordinate is that the small difference of adsorption parameter is amplified to large difference of its value. 

This table shows that it is diflicult, even in a model system, to present a simple view of the nature of the adsorption site because of the number of different parameters involved in the stabilization of OJ. For zeolites the problem is apparently more diflicult than for oxides, since not only do the framework ions and the exchanged cations form two distinct types of adsorption sites but the latter can migrate within the zeolite structure. It is difficult to obtain a full description of the coordination of the exchanged cations and so far there has been no systematic study on this point. 

Values of the parameter 0 may be experimentally evaluated for the mercury-water surface from electrocapillary studies. The displacement of the coordinates of the electrocapillary maxima in Figure 7.23 reflects differences in the intrinsic adsorbability of various ions. Electrocapillary studies reveal that the strength of specific adsorption at the mercury-water interface for some monovalent anions follows the order... 

To study further the nature of the coordinated 02 molecule, adsorption experiments with 170180 were carried out. Figure 3 shows an EPR spectrum of the ammoniated Co(II)Y zeolites, treated with 170180. Since the nuclear spin of 170 is 5/2, paramagnetic species with one 170 have 21 + 1 or six lines. Two sets of six hyperfine lines (170180) can be observed in addition to the cobalt hyperfine lines. The paramagnetic parameters of 170 species are given in Table II. These values, including the g tensor, are comparable with those observed in several studies of the superoxide ion on various oxides (15). 

Additional information on adsorption mechanisms and models is in Stollenwerk (2003), 93-99 and Prasad (1994). Foster (2003) also discusses in considerable detail how As(III) and As(V) may adsorb and coordinate on the surfaces of various iron, aluminum, and manganese (oxy)(hydr)oxides. In adsorption studies, relevant laboratory parameters include arsenic and adsorbent concentrations, adsorbent chemistry and surface area, surface site densities, and the equilibrium constants of the relevant reactions (Stollenwerk, 2003), 95. Once laboratory data are available, MINTEQA2 (Allison, Brown and Novo-Gradac, 1991), PHREEQC (Parkhurst and Appelo, 1999), and other geochemical computer programs may be used to derive the adsorption models. 

Each monomer is ascribed with a two-dimensional coordinate, of which the abscissa dimension corresponds to the affinity to the polar (water) or the nonpolar phase (hexane) and the ordinate dimension corresponds to interfacial activity. The standard free energy of partition between water and hexane is used as a quantitative parameter for the abscissa axis (AFpart), whereas the standard energy of adsorption at the interface is used for the ordinate axis (AFa(js). Both parameters are normalized by the kT factor. The normalized values are denoted as A/part and A/ads, respectively. Thus,... 

Here E ( y1 ) stands for the single-particle contribution to the total energy, allowing for molecule interaction with the surface <2 is the heat released in adsorption of molecules z on the /Lh site Fj the internal partition function for the z th molecules adsorbed on the /Lh site F j the internal partition function for the zth molecule in the gas phase the dissociation degree of the z th molecule, and zz the Henry local constant for adsorption of the zth molecule on the /Lh site. Lateral interaction is modeled by E2k([ylj ), and gj (r) allows for interaction between the z th and /Lh particles adsorbed on the /th and gth sites spaced r apart. In the lattice gas model, separations are conveniently measured in coordination-sphere numbers, 1 < r < R. For a homogeneous surface, molecular parameters zz and ej(r) are independent of the site nature, while for heterogeneous, they may depend on it. 

Fig. 2.16 displays experimental data on the luminescence quenching of CdS colloidal particles of four different size in the Stem-Folmer s coordinates. The data correspond to different luminescence bands. This figure presents also the curves approximating the experimental points to equation (2.19). From these curves, the values of the both parameters, KadS and A, may be extracted. One may see from Fig. 2.16 that the luminescence quenching of CdS by methylviologen differs for different bands and depends on the size of colloidal particles. In particular, the methylviologen adsorption constant rises as the size of the CdS colloidal particles increases. It follows from Fig. 2.17 that the obtained values of rate constant Kads decrease exponentially with an increase of the value opposite to the colloidal particle diameter. 

Kivelson and Niemann [301] showed that both An and gn correlate well with the type of ligand atoms bound to Cu2+ and with the polyhedron structure [301-303]. Therefore, changes in the EPR spectrum shape and parameters have to reflect rearrangements in the coordination sphere. Fig. 8.22 presents typical EPR spectra of Cu(II) complexes adsorbed onto nanocrystalline Ti02 particles from solutions containing Cu(N03)2 and edta at the ratio [Cu] [edta] = 1 1 at different pH values. The line-shape analysis showed that at pH 2.9 and 8.0 the EPR spectra are a superposition of the spectra of at least two different species, while the spectrum, recorded for the sample prepared at pH 6.9 with a short (1 h) time of adsorption, indicates the formation of only one Cu2+ species at the surface (type A ). 

Experimental data for obtained in the present work for adsorption of H2 and D2 on NPC have been treated in coordinates of equation (2). For pressure more then 20 kPa parameters of equation (2) are given in Table 1. These values were calculated from experimental data obtained within relatively narrow range of pressure and so they are just synthetic coefficients, not constants. 

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