Coadsorption

Diehl R D and McGrath R 1996 Structural studies of alkali metal adsorption and coadsorption on metal surfaces Surf. Sc/. Rep. 23 43... 

Zaera F, Fischer D A, Shen S and Gland J L 1998 Fluorescence yield near-edge X-ray absorption spectroscopy under atmospheric conditions CO and FI2 coadsorption on Ni(IOO) at pressures between 10 and 0.1 Torr Surf. Sc/. 194 205-16... 

Wu S, Lipkowski J, Tyiiszczak T and Hitchcock A P 1997 Eariy stages of copper eiectrocrystaiiization eiectrochemicai and in situ x-ray absorption fine structure studies of coadsorption of copper and chioride at the Au(111) eiectrode surface J.Phys. Chem. B 101 10 310-22... 

Li J and Abruna FI D 1997 Coadsorption of sulphate/bisulphate anions with Fig cations during Fig underpotential deposition on Au (111) An In situ x-ray diffraction study J. Phys. Chem. B 101 244-52... 

It has been suggested that the first step, weak coadsorption of NO and O2 on a reduced vanadium site, may represent the slow step in the mechanism. Subsequent formation of a N202-like intermediate could be a fast step, because it is known that in the gas phase the equiUbrium of NO—NO2 and N2O2 is estabflshed within microseconds (35). 

Lateral interactions between the adsorbed molecules can affect dramatically the strength of surface sites. Coadsorption of weak acids with basic test molecules reveal the effect of induced Bronsted acidity, when in the presence of SO, or NO, protonation of such bases as NH, pyridine or 2,6-dimethylpyridine occurs on silanol groups that never manifest any Bronsted acidity. This suggests explanation of promotive action of gaseous acids in the reactions catalyzed by Bronsted sites. Just the same, presence of adsorbed bases leads to the increase of surface basicity, which can be detected by adsorption of CHF. ... 

Secondly, absorbent particles such as charcoal and soot are intrinsically inert but have surfaces or infrastructures that adsorb SO, and by either coadsorption of water vapour or condensation of water within the structure, catalyse the formation of a corrosive acid electrolyte solution. Dirt with soot assists the formation of patinae on copper and its alloys by retaining soluble corrosion products long enough for them to be converted to protective, insoluble basic salts. 

Figure 6. Effect of coadsorption of water with other species on Cu(110). (a) Coadsorption...

For associative (not dissociative) coadsorption of A and B on a catalyst surface the Langmuir isotherm takes the form ... 

This type of isotherm is more realistic for describing chemisorption at intermediate 0a values but quickly leads to mathematically cumbersome or intractable expressions with many unknown parameters when one considers coadsorption of two gases. One needs to know how -AHa is affected both by 0A and by the coverages of all other adsorbates. Thus for all practical purposes the LHHW kinetics represent even today the only viable approach for formulating mathematically tractable, albeit usually highly inaccurate, rate expressions for catalytic kinetics. In Chapter 6 we will see a new, medium field type, approach which generalizes the LHHW kinetics by accounting also for lateral interactions. 

Electronegative adatoms cause significant changes in the metal surface electronic stmcture, manifest as changes in the surface work function. In general electronegative additives increase the work function of the metal substrate. Typical examples are shown in Figures 2.9 and 2.10 for the adsorption of Cl and coadsorption of Cl and O on the work function of... 

Similar is the effect of S coadsorption on the CO TPD spectra on Pt(lll) as shown in Figure 2.29. Sulfur coadsorption weakens significantly the chemisorptive bond of CO. 

As expected, the CO dissociation propensity is reduced in the presence of electronegative modifiers. This is manifest, for example, by the gradual elimination of the (3-peak in CO TPD spectra upon coadsorption of electronegative modifier (Figs. 2.28, 2.29 and 2.30). 

Thus, it may again be concluded, as in the case of alkali coadsorption with H, that chemisorbed H exhibits amphoteric, i.e. both electron donor and electron acceptor characteristics. 

The coadsorption of oxygen as well as of other electronegative additives on metal surfaces favors in general the 7t-bonded molecular state of ethylene, as the latter exhibits, compared to the di-o bonded state, a more pronounced electron donor character and a negligible backdonation of electron density from the metal surface. 

S. Surnev, and M. Kiskinova, Formation of Patchy Surface Overlayers Alkali Adsorption and Alkali Cabon Monoxide and oxygen coadsorption on Ru(001) and Ru(10l 0 Appl. Phys. 46, 323-329 (1988). 

K.J. Maynard, and M. Moskovits, A surface enhanced Raman study of carbon dioxide coadsorption with oxygen and alkali metals on silver surfaces,/. Chem. Phys. 90(11), 6668-6679 (1989). 

Even with the simpler Frumkin or Fowler-Guggenheim approach (Eqs. 6.50 and 6.52), treating the coadsorption and surface reaction of different adsorbates leads immediately to mathematically intractable expressions and to the introduction of new parameters, whereas equation... 

Figures 7.9 and 7.10 are simply simulations based on assumed interaction energies. The lateral interactions for specific cases can only be derived from measurement in favorable cases, such as the following example on the coadsorption of CO and N atoms.

Oxygen Interactions and Reactions on Palladium(lOO) Coadsorption Studies with C2H4, H2O, and CH3OH... 

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