Chemisorption of gases

The adsorption of nonelectrolytes at the solid-solution interface may be viewed in terms of two somewhat different physical pictures. In the first, the adsorption is confined to a monolayer next to the surface, with the implication that succeeding layers are virtually normal bulk solution. The picture is similar to that for the chemisorption of gases (see Chapter XVIII) and arises under the assumption that solute-solid interactions decay very rapidly with distance. Unlike the chemisorption of gases, however, the heat of adsorption from solution is usually small it is more comparable with heats of solution than with chemical bond energies. 

The Elovich model was originally developed to describe the kinetics of heterogeneous chemisorption of gases on solid surfaces [117]. It describes a number of reaction mechanisms including bulk and surface diffusion, as well as activation and deactivation of catalytic surfaces. In solid phase chemistry, the Elovich model has been used to describe the kinetics of sorption/desorption of various chemicals on solid phases [23]. It can be expressed as [118] ... 

The Elovich equation was developed to determine the kinetics of heterogeneous chemisorption of gases on sohd surfaces. This equation assumes a heterogeneous distribution of adsorption energies, where the energy of activation E) increases linearly with surface coverage (Rao et al. 1989). A simplified Elovich equation used to study the rate of soil chemical processes is given by... 

There have been many attempts to relate bulk electronic properties of semiconductor oxides with their catalytic activity. The electronic theory of catalysis of metal oxides developed by Hauffe (1966), Wolkenstein (1960) and others (Krylov, 1970) is base d on the idea that chemisorption of gases like CO and N2O on semiconductor oxides is associated with electron-transfer, which results in a change in the electron transport properties of the solid oxide. For example, during CO oxidation on ZnO a correlation between change in charge-carrier concentration and reaction rate has been found (Cohn Prater, 1966). 

TOMPKINS, F.C., Chemisorption of Gases on Metals, Academic Press (1978)... 

Chemisorption of gases on carbonaceous surfaces has been considered in... 

Books. M. W. Roberts, Chemistry of the Metal-Gas Interface , Oxford University Press, Oxford, 1978 F. C. Tompkins, Chemisorption of Gases on Metals , Academic Press, London, 1978 Experimental Methods in Catalysis Research , ed. R. B. Anderson and P. T. Dawson, Academic Press, London, 1976 Chemistry and Physics of Solid Surfaces , ed. R. Vanselow and S. Y. Yong, CRC Press, Cleveland, Ohio, 1977 Advances in Characterisation of Metal and Polymer Surfaces , ed. L. H. Lee, Academic Press, New York, 1976 K. Tamaru, Dynamic Heterogeneous Catalysis , Academic Press, London, 1978 The Solid-Vacuum Interface , ed. A. van Oostrom and M. J. Sparnay, Surface Sci., 1977, 64 Electron Spectroscopy , ed. C. R. Brundle and A. D. Baker, Academic Press, New York, 1977, Vol. 1 Auger Electron Spectroscopy (Bibliography 1925—1975) , compiled by D. T. Hawkins, Plenum, New York, 1977. 

Chemisorption of gases such as H2 and CO can determine the surface area of specific reduced metal surface species (and thus the dispersion and average cluster size). 

Tompkins (1978) concentrates on the fundamental and experimental aspects of the chemisorption of gases on metals. The book covers techniques for the preparation and maintenance of clean metal surfaces, the basic principles of the adsorption process, thermal accommodation and molecular beam scattering, desorption phenomena, adsorption isotherms, heats of chemisorption, thermodynamics of chemisorption, statistical thermodynamics of adsorption, electronic theory of metals, electronic theory of metal surfaces, perturbation of surface electronic properties by chemisorption, low energy electron diffraction (LEED), infra-red spectroscopy of chemisorbed molecules, field emmission microscopy, field ion microscopy, mobility of species, electron impact auger spectroscopy. X-ray and ultra-violet photoelectron spectroscopy, ion neutralization spectroscopy, electron energy loss spectroscopy, appearance potential spectroscopy, electronic properties of adsorbed layers. 

B.E.Nieuwenhuys, "Chemisorption of Gases on Metal Films", P.Wissmann,ed. Chapter 8, Elsevier, Amsterdam (1987)... 

For a surface-catalyzed reaction to occur, chemical bonds must be involved, and so our interest is primarily with chemisorption. Again, some general classifications of various metals for chemisorption of gases are possible, as shown in Table 2.1-3 from Coughlin [26], and similar properties are involved. Note that the transition elements of the periodic table are frequently involved, and this appears to be based on the electronic nature of their d-orbitals. 

The chemisorption of gases on metals has been the subject of particularly intensive investigations, and the available data allow the catal5hic properties of metals to be explained well. Experimentally determined, quahtative orders of catalytic effectiveness are often found in the literature. For example, for the adsorption of hydrocarbons ... 

Biunauer S, Emmett PH (1940) Chemisorptions of gases on iron synthetic ammonia catalysts. J Am Chem Soc 62 1732-1746... 

Chemisorption of gases over solids is often used for metallic surface area and dispersion of particles on supported catalysts analyses. Table 10.2 presents some properties comparing the physical and chemical adsorptions. 

The number of important chemical processes that involve the chemisorption of gases at solid surfaces is quite large and cannot be even partially covered here. However, a few general examples of reaction types include... 

Hence, any one of these two parameters, in the present study, can be used to represent the other. In catalyst preparations where Pt or Ir dispersions in /- alumina can not be practically determined using the known techniques of chemisorption of gases, e.g., Hz or CO, the metal distribution data can be used Instead. 

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