Adsorption sequence

Fig. 4. Activity versus water adsorption , hydrogen adsorption sequence O, ethylene adsorption sequence.

Thermochemical Cycle Testing the Formation of Gaseous Carbon Dioxide at the End of the Adsorption Sequence (CO—O2—CO)"... 

Heat-flow microcalorimetry may be used, therefore, not only to detect, by means of adsorption sequences, the different surface interactions between reactants which constitute, in favorable cases, the steps of probable reaction mechanisms, but also to determine the rates of these surface processes. The comparison of the adsorption or interaction rates, deduced from the thermograms recorded during an adsorption sequence, is particularly reliable, because the arrangement of the calorimetric cells remains unchanged during all the steps of the sequence. Moreover, it should be remembered that the curves on Fig. 28 represent the adsorption or interaction rates on a very small fraction of the catalyst surface which is, very probably, active during the catalytic reaction (Table VI). It is for these... 

Valette [119] has used the dependence of the minimum of the double-layer capacitance on the concentration of the supporting electrolyte to find the adsorption sequence of anions on Ag(llO) face ... 

Values obtained from isotherms at —195 C. after adsorption sequence at higher temperatures. 

Adsorption sequence Total C4 Hydrocarbon adsorbed c Amount of C02 normally desorbed 8... 

At a lower initial coverage of N and 0 adatoms (Fig. 6), the NO can adsorb first into the (vacant) bridged sites, which are energetically preferred. These conclusions are reminiscent of those drawn from previous UPS studies of the adsorption of NO on Ru(100) at 370 K, in which dissociation of NO was shown to precede adsorption of molecular NO in coverage (7). This adsorption sequence has also been postulated to occur on polycrystalline Rh at room temperature on the basis of CO titration experiments (55). 

FIGURE 7 Adsorption isotherms corresponding to the three adsorption sequences shown in Fig. 8 (the cmc is indicated by the arrow). 

Calorimetry can help elucidate the mechanisms of heterogeneously catalyzed reactions (1, 3). Possible reaction steps can be studied in the calorimeter by means of successive adsorption sequences, whereas reaction mechanisms, including different series of steps, can be tested in thermochemical cycles. However, the following limitations of the approach should be noted (i) (1) adsorption sequences only involve irreversibly adsorbed species, since... 

Similar observations, regarding the adsorption sequences of cations and anions, have also been made for other oxides (a-Fe203, ZnO) and have led to a description of such oxide surfaces as structure promoting This representation constitutes an extension of the Gurney s interpretation of ion-ion interactions in solution to the ion-surface interactions. 

Dumont, E, Verbeiren, P. and Buess-Herman, C., Adsorption sequence of the alkali cations at the tungsten trioxide-water interface. Colloids Surf. A, 154, 149, 1999. 

Dumont, E, Warlus, J., and Watillon, A., Influence of the point of zero charge of titanium dioxide hydrosols on the ionic adsorption sequences, J. Colloid Interf. Sci., 138, 543, 1990. 

Desorption of the complete Pb adlayer within the three distinct desorption peaks D3, D2 and D1 (see Fig. 2) by step polarization proceeds in an analogous way to the adsorption sequence, except on the monoatomic islands in contrast to the complete adsorbate formation at the islands in peak A3, desorption in peak D3 only involves the outermost part of the monolayer at the island periphery, whereas the remaining adsorbate coverage is completely desorbed in peak D2. Desorption on the monoatomic islands occurs thus in the same way as at the stepped terrace domains, except for the missing step decoration coverage desorbed in D1. 

The uptake of molecules into the a-CO phase appears to be very dependent on the adsorption temperature and the gas phase pressure. Ehrlich quotes an a-phase concentration when CO is adsorbed at 130°K as being approximately 30 times that at room temperature during the early stages of adsorption since at the lower temperature the concentration of this phase increases earlier in the adsorption sequence. The variation in a-phase concentration with pressure was found to be less significant, but could be readily observed for temperatmes close to, or above, room temperature. The )3 phase on the other hand was found to be totally independent of pressure. 

In observing an adsorption sequence, it has been our practice to start... 

For adsorption on alumina, the following adsorption sequences have been reported (i = lluoro. chloro, bromo, nitro, or carbomethoxy) (57) ... 

The /7-bis(phenylazo)benzenes show the anomalous adsorption sequence cisjrans > cis, cis >trans, ti ans. This has been attributed (21) to the nonplanar configuration of the cis isomers and a resulting difficulty in the optimum adsorption of each azo group in thec/s, cis isomer. 

Fig. 3(a, b, c). Oxygen adsorption sequence of field-emission patterns from the same tungsten tip used in Fig. 2. 

Different sequences of adsorption were studied with SPR measurements. One of the typical set of SPR curves, corresponding to an adsorption sequence of PAA/protein-A/IgG/anti-IgG, is shown as an example in Fig. 12. Adsorption of relatively small molecules of the protein-A causes a little shift of the SPR curve, while adsorption of bulky IgG and anti-lgG molecules leads to a substantial shift. The values of the effective thickness of the adsorbed layers were evaluated by fitting of the experimental data to Fresnel s theory, and the results are presented on the inset to Fig. 12 as a bar-chart diagram. 

Fig. 12 Typical SPR curves for the adsorption sequence of (1) PAA layer on top of gold, (2) protein-A on top of PAA, (3) IgG on top of protein-A, (4) anti-lgG/IgG specific interaction. The inset shows the effective thicknesses of the adsorbed layers...

Figure 8 AFM height (a) and friction force (b) images of the hydrophilically (5 Xm)/ hydrophobically (10 pm) patterned substrate and of single organometallic bilayers adsorbed on this prepattemed substrate. Adsorption sequence cation-anion (c,d), anion-cation (e,f). In both cases the bUayer is selectively adsorbed on the hydrophobic areas. (Reproduced with permission from Ref. 17, 2002 ACS.)...

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