Surface dissociation

The various TPR peaks may correspond to different active sites. One hypothesis assumed cyclization over metallic and complex (Section II,B,4) platinum sites (62e) the participation of various crystallographic sites (Section V,A) cannot be excluded either. Alternatively, the peaks may represent three different rate determining steps of stepwise aromatization such as cyclization, dehydrogenation, and trans-cis isomerization. If the corresponding peak also appears in the thermodesorption spectrum of benzene, it may be assumed that the slow step is the addition of hydrogen to one or more type of deeply dissociated surface species which may equally be formed from adsorbed benzene itself (62f) or during aromatization of various -Cg hydrocarbons. Figure 11 in Section V,A shows the character of such a species of hydrocarbon. 

The formation of methylcyclopentane from hexanes proceeds in the presence of hydrogen only (27, 27a). A singly dissociated surface intermediate is suggested by the hydrogen order of about — 1 on the right-hand side of the bell-shaped curves over platinum black between 300° and 360°C (Fig. 6) (77). 

Dissociative surface reaction and its reverse, associative surface reaction. 

Grinberg, H., Freed, K.F., and Williams, C.J. (1987). Three-dimensional analytical quantum mechanical theory for triatomic photodissociation Role of angle dependent dissociative surfaces on rotational and angular distributions in the rotational infinite order sudden limit, J. Chem. Phys. 86, 5456-5478. 

For heterogeneous systems, the set of reactions includes adsorption, dissociation, surface diffusion, desorption, and other processes. In this case, the rates of processes can differ by many orders of magnitude. In accordance with Eq. (30), the time step is determined by the fastest process in the system. This condition strongly restricts the maximum real time in the simulation and prevents modeling of rare processes. One of the ways of overcoming this problem can be to exclude all fast processes from the table of reactions and use equilibrium distributions for these processes. For example,... 

The molecular structure of retinoic acid is typical for an amphiphilic compound that is concentrated at interfaces. Further, the carboxylic acid groups allow such compounds to adjust their amphiphilic character by the degree of their dissociation. Surface tension measurements were carried out in order to determine the surface activity of retinoic acid [179]. The surface tension with respect to the concentration at pH 5 decreases more strongly than at pH 9. This reflects the fact that the protonated form of retinoic acid is more efficient in its surface activity than the deprotonated form. The critical micelle concentrations are 3.7 0.5 mg/L (pH 5) and 19 2 mg/L (pH 9). The limiting surface tension values in both curves is about 35 mN/m. Due to the precipitation of retinoic acid, the highest concentration in the surface tension curve at a pH of 5 was 20 mg/L. By contrast the solubility at pH 9 is at least 1 g/L. In order to verify the results from the FTIR measurements, films of the complexes were immersed in a solution of 0.15 mol/L sodium... 

There are various mannas in which ion-specific effects can be accounted for by the polarization model. The first one is related to the different association constants of the ions with the dissociated surface groups. The charging of the surface depends not only on the electrolyte concentration, but also on the type of electrolyte. These ion-specific effects are similar to those predicted by the traditional theory [46]. A typical consequence of such effects is illustrated by the dependence of the isoelectric point on the nature of electrolyte [21]. 

Reuter, Frenkel, and Scheffler have recently used DFT-based calculations to predict the CO turnover frequency on RuO2(110) as a function of 02 pressure, CO pressure, and temperature.31 This was an ambitious undertaking, and as we will see below, remarkably successful. Much of this work was motivated by the earlier success of ab initio thermodynamics, a topic that is reviewed more fully below in section 3.1. The goal of Reuter et al. s work was to derive a lattice model for adsorption, dissociation, surface diffusion, surface reaction, and desorption on defect-free Ru02(l 10) in which the rates of each elementary step were calculated from DFT via transition state theory (TST). As mentioned above, experimental evidence strongly indicates that surface defects do not play a dominant role in this system, so neglecting them entirely is a reasonable approach. The DFT calculations were performed using a GGA full-potential... 

For dilute solutions of a completely dissociated surface-active 1 1 electrolyte in the presence of a swamping, constant amount of electrolyte containing a common nonsurfactant counterion,... 

The proposed reaction mechanism includes adsorption, dissociation, surface reaction and desorption steps. The adsorbed species are denoted by H, D and HD, where is an active empty site on the surface. The rates of the elementary steps are given by the following equations for the gas phase species and surface species respectively... 

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