THEORIES OF CHEMISORPTION

Whitten J L and Yang H 1996 Theory of chemisorption and reactions on metal surfaces Surf. Sc/. Rep. 24 59-124... 

O showed a profound difference in CO2 formation rate [M.J.P. Hopstaken and J.W. Niemantsverdriet, J. Chem. Phys. 113 (2000) 5457]. Hence, care should be taken to interpret apparent structure sensitivity found under normal operating conditions of high pressure and coverage in terms of the intrinsic reactivity of sites. From the theory of chemisorption and reaction discussed in Chapter 6 it is hard to imagine how the concept of structure insensitivity can be maintained on the level of individual sites on surfaces, as atoms in different geometries always possess different bonding characteristics. 

The second part of the paper Is devoted to some aspects of the current status of the theory of chemisorption There, in particular, Che adsorption of water and ammonia will be studied and discussed Through the theory a qualitative understanding of the bonding of these molecules to surfaces Is achieved which Is In agreement with Che experimental observations ... 

Davison SG, Sulston KW. 2006. Green Eunction Theory of Chemisorption. London Springer Verlag. 

In Chapter 1 we consider the physical and diemical basis of the method of semiconductor chemical sensors. The items dealing with mechanisms of interaction of gaseous phase with the surface of solids are considered in substantial detail. We also consider in this part the various forms of adsorption and adsorption kinetics processes as well as adsorption equilibria existing in real gas-semiconductor oxide adsorbent systems. We analyze the role of electron theory of chemisorption on... 

The role of electronic theory of chemisorption in developing ideas on effects of adsorption on electrical and physical properties of semiconductor adsorbents. 

The principal idea of Volkenshtein, the founder of electronic theory of chemisorption, was that chemisorbed particle and solid body form a unified quantum mechanical system. During the analysis of such systems one should account for the change in electronic state of both adparticle and the adsorbent itself [9]. In other words, in this case adsorption provides for a chemical binding of molecules with adsorbent. 

In conclusion we would like to mention that basic ideas which formed a ground-stone of the Volkenshtein electron theory of chemisorption have been confirmed and substantially developed in numerous... 

It has been proven by experiment that there are donor acceptor atoms and molecules of absorbate and their classification as belonging to one or another type is controlled not only by their chemical nature but by the nature of adsorbent as well (see, for instance [18, 21, 203-205]). From the standpoint of the electron theory of chemisorption it became possible to explain the effect of electron adsorption [206] as well as phenomenon of luminescence of radical recombination during chemisorption [207]. The experimental proof was given to the capability of changing of one form of chemisorption into another during change in the value of the Fermi level in adsorbent [208]. 

J R Smith, Ed, Theory of Chemisorption, Sprmger-Verlag, Berlin, 1980... 

The photoadsorption effect as such does not constitute the subject matter of the present article. We shall consider it very briefly, only to the extent necessary to allow one to draw analogies between the mechanisms of the photoadsorptive and photocatalytic effects. The photoadsorptive effect has been studied sufficiently well. A brief summary of the experimental data will be given below. The mechanism of the phenomenon has been thoroughly discussed in a number of theoretical works from the standpoint of the electronic theory of chemisorption and catalysis C3,4,6-8). 

A number of theoretical works have been devoted to the study of the hydrogen-deuterium exchange reaction. Hauffe (25) examined this reaction from the standpoint of the boundary layer theory of chemisorption. Dowden and co-workers (26) undertook a theoretical investigation of the hydrogen-deuterium exchange reaction from the viewpoint of the theory of crystalline fields. 

We shall consider the hydrogen-deuterium exchange reaction from the viewpoint of the electronic theory of chemisorption and catalysis (27),... 

It has also to be remembered that the band model is a theory of the bulk properties of the metal (magnetism, electrical conductivity, specific heat, etc.), whereas chemisorption and catalysis depend upon the formation of bonds between surface metal atoms and the adsorbed species. Hence, modern theories of chemisorption have tended to concentrate on the formation of bonds with localized orbitals on surface metal atoms. Recently, the directional properties of the orbitals emerging at the surface, as discussed by Dowden (102) and Bond (103) on the basis of the Good-enough model, have been used to interpret the chemisorption behavior of different crystal faces (104, 105). A more elaborate theoretical treatment of the chemisorption process by Grimley (106) envisages the formation of a surface compound with localized metal orbitals, and in this case a weak interaction is allowed with the electrons in the metal. 

The current theory of chemisorption on semiconductors as developed by Hauffe 14) assumes that charge is transferred either from or to the solid, so that the chemisorbed species exists on the surface as an ion. The resulting surface charge is balanced by a charge in the solid associated with the discrete electron levels which are responsible for the semiconducting properties of the solid. It would appear at first sight that the existence of localized states for the combined system, foreign atom plus crystal, is required... 

The results of the electron theory as developed for semiconductors are fully applicable to dielectrics. They cannot, however, be automatically applied to metals. Contrary to the case of semiconductors, the application of the band theory of solids to metals cannot be considered as theoretically well justified as the present time. This is especially true for the transition metals and for chemical processes on metal surfaces. The theory of chemisorption and catalysis on metals (as well as the electron theory of metals in general) must be based essentially on the many-electron approach. However, these problems have not been treated in any detail as yet. 

Eucken (88,89) and Wicke (90) have tried to explain the dehydrogenation and dehydration of isopropyl alcohol by an electron interchange between the alcohol and the zinc oxide alumina catalysts used for these conversions. We shall modify the mechanism proposed by Eucken and Wicke, following the theory of chemisorption. Contrary to these authors, we do not believe that the positions of the zinc and oxygen ions on the surface of the zinc oxide catalysts have any appreciable influence upon... 

In the above, we have discussed a theory of chemisorption. It is based on a very simple model of the electronic levels and of the possible reactions. 

This appendix begins with a brief introduction to the physics of metal surfaces. We limit ourselves to those properties of surfaces that play a role in catalysis or in catalyst characterization. The second part includes an introduction to the theory of chemisorption, and is intended to serve as a theoretical background for the chapters on vibrational spectroscopy, photoemission, and the case study on promoter effects. General textbooks on the physics and chemistry of surfaces are listed in [1-8]. 

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