Structure-sensitive adsorption

Clavilier J, Feliu JM, Aldaz A. 1988. An irreversible structure sensitive adsorption step in bismuth underpotential deposition at platinum electrodes. J Electroanal Chem 243 419-433. 

The value of this approach is to differentiate between the structure sensitive adsorption, of Stage 1, which involves the initial high heats of adsorption extensive adsorption, at pressures above 1(T mm. with an undetermined upper limit and a low heat of adsorption, which is responsible for the parahydrogen conversion and the slow sorption process with an appreciable heat of sorption which causes poisoning of the parahydrogen conversion. The work can give no indication of the physical processes involved in the three types of adsorption. 

During the past two decades, a great deal of work in surface electrochemistry has been aimed at elucidating the role of the local symmetry of surface atoms in electrocatalysis, particularly for the kinetics of the ORR on platinum single-crystal surfaces. It is now well established that the kinetics of the ORR on Pt(hkl) surfaces are sensitive to the surface structure [88, 89] and arise because of structure-sensitive adsorption of spectator species, such as H plimited scope of this report, it will not be possible to review aU... 

In contrast with the extensive studies of the ORR on Pt(hkl) surfaces, there has been no substantial fundamental study of the effects of anion adsorption on the kinetics of the ORR on Cu(hkl) surfaces. Very recently, by utilizing the RRDE technique, Brisard and coworkers [101] have shown that the ORR on Cu(lll) and Cu(OOl) surfaces in sulfuric acid solution is a structure-sensitive process, see Fig. 31. As for Pt(hkl), an interpretation of the variation in the activity of this process with the different low-index crystal surfaces of Cu can be presented on the basis of the premise of the structure-sensitive adsorption of sulfuric acid anions on Cu(hkl) surfaces, for example, as for Pt(hkl) with the (1 — ad) term. 

We first discuss the structure sensitivity on the same metal substrates. The fact that the kinetics of the ORR on Pt(hkf) (Figs. 28 and 29), Cu(hkl) (Fig. 31), and Au hkl) (Fig. 32) are orders of magnitude lower in acid solutions containing strongly adsorbing anions indicates that the structure sensitivity is due primarily to the structure-sensitive adsorption of spectator species, for example, by the (1 — aa) term. The (1 — aa) term is determined by both the pzc of the substrate as well as the match... 

Very recently, considerable effort has been devoted to the simulation of the oscillatory behavior which has been observed experimentally in various surface reactions. So far, the most studied reaction is the catalytic oxidation of carbon monoxide, where it is well known that oscillations are coupled to reversible reconstructions of the surface via structure-sensitive sticking coefficients of the reactants. A careful evaluation of the simulation results is necessary in order to ensure that oscillations remain in the thermodynamic limit. The roles of surface diffusion of the reactants versus direct adsorption from the gas phase, at the onset of selforganization and synchronized behavior, is a topic which merits further investigation. 

Hammer B, Nielsen OH, Nprskov JK. 1997. Structure sensitivity in adsorption CO interaction with stepped and reconstructed Pt surfaces. Catal Lett 46 31. 

Numerous quantum mechanic calculations have been carried out to better understand the bonding of nitrogen oxide on transition metal surfaces. For instance, the group of Sautet et al have reported a comparative density-functional theory (DFT) study of the chemisorption and dissociation of NO molecules on the close-packed (111), the more open (100), and the stepped (511) surfaces of palladium and rhodium to estimate both energetics and kinetics of the reaction pathways [75], The structure sensitivity of the adsorption was found to correlate well with catalytic activity, as estimated from the calculated dissociation rate constants at 300 K. The latter were found to agree with numerous experimental observations, with (111) facets rather inactive towards NO dissociation and stepped surfaces far more active, and to follow the sequence Rh(100) > terraces in Rh(511) > steps in Rh(511) > steps in Pd(511) > Rh(lll) > Pd(100) > terraces in Pd (511) > Pd (111). The effect of the steps on activity was found to be clearly favorable on the Pd(511) surface but unfavorable on the Rh(511) surface, perhaps explaining the difference in activity between the two metals. The influence of... 

Both the data on hydrogen adsorption and formic acid oxidation show pronounced structural sensitivity, thus confirming a paramount role of surface structure in electrocatalytic reactions. It can be concluded that each crystallographic orientation represents a distinct electrochemical (chemical) entity. The investigation of stepped surfaces seems to be necessary to reach an understanding of these systems on a molecular level. Hydrogen adsorption shows dependences on the terrace orientation, step orientation, and step density. All the... 

Asymmetric diarylmethanes, hydrogenolytic behaviors, 29 229-270, 247-252 catalytic hydrogenolysis, 29 243-258 kinetics and scheme, 29 252-258 M0O3-AI2O3 catalyst, 29 259-269 relative reactivity, 29 255-257 schematic model, 29 254 Asymmetric hydrogenations, 42 490-491 Asymmetric synthesis, 25 82, 83 examples of, 25 82 Asymmetry factor, 42 123-124 Atom-by-species matrix, 32 302-303, 318-319 Atomic absorption, 27 317 Atomic catalytic activities of sites, 34 183 Atomic displacements, induced by adsorption, 21 212, 213 Atomic rate or reaction definition, 36 72-73 structure sensitivity and, 36 86-87 Atomic species, see also specific elements adsorbed... 

Adsorption at Low Pressure (P < 10" Torr). The adsorption of propene has been studied with thermal desorption spectroscopy (TDS) on all of the different forms of the (100) and (111) surfaces and under several different conditions of exposure. For exposures at low pressure (P< 10 Torr), no selective oxidation is observed. For small exposures (< 5 L) at low-temperature (100K-120K), four propene desorption states are observed from the Ci O(lll) surface comparecf to two desorption states from the Cu9O(100)-Cii surface. These TDS results are shown in Figure 3, and give a cfear indication of a structure-sensitive interaction of propene with Cu20. 

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