Adsorption of gas

In general, the adsorption behaviour of gases on iron oxides has been investigated either because the gases are atmospheric pollutants (NO, SO2, CO2), or because they act as probe molecules and provide information about surface sites. The adsorption sites on iron oxides are usually the Lewis acid sites. 

Goethite CO2 SO2 pyridine, acetic acid vapour, CO2, nitric oxide, trimethyl chlorosilane Russell et ah, 1975 Kaneko and Inouye, 1981 Rochester and Topham, 1979 c 

Hematite NH3, H2S, ETOH, ET2OH, N2, O2, H2, CO, SO2, CI2, C2H6, C2H4 Blyholder and Richardson, 1962 

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D. M. Young and A. D. Crowell, Physical Adsorption of Gases, Butterworths, London, 1962. 

S. Brunauer, The Adsorption of Gases and Vapors, Vol. 1, Princeton University Press, Princeton, NJ, 1945. 

TPD Temperature programmed desorption After pre-adsorption of gases on a surface, the desorption and/or reaction products are measured while the temperature Increases linearly with time. Coverages, kinetic parameters, reaction mechanism... 

B) TYPICAL ISOTHERMS FOR THE PHYSICAL ADSORPTION OF GASES ON SURFACES... 

The physical adsorption of gases by non-porous solids, in the vast majority of cases, gives rise to a Type II isotherm. From the Type II isotherm of a given gas on a particular solid it is possible in principle to derive a value of the monolayer capacity of the solid, which in turn can be used to calculate the specific surface of the solid. The monolayer capacity is defined as the amount of adsorbate which can be accommodated in a completely filled, single molecular layer—a monolayer—on the surface of unit mass (1 g) of the solid. It is related to the specific surface area A, the surface area of 1 g of the solid, by the simple equation... 

Fig. 2.6 Adsorption of gases on silver foil. (a) BET plots h) adsorption isotherms. (Solid symbols are desorption points.) (Courtesy Davis, Dc Witt...

The incorporation of the new material without any increase in the overall length of the book has been achieved in part by extensive re-writing, with the compression of earlier material, and in part by restricting the scope to the physical adsorption of gases (apart from a section on mercury porosimetry). The topics of chemisorption and adsorption from solution, both of which were dealt with in some detail in the first edition, have been omitted chemisorption processes are obviously dependent on the chemical nature of the surface and therefore cannot be relied upon for the determination of the total surface area and methods based on adsorption from solution have not been developed, as was once hoped, into routine procedures for surface area determination. Likewise omitted, on grounds of... 

W. Rudzinski, D. H. Everett. Adsorption of Gases on Heterogeneous Surfaces. New York Academic Press, 1992. 

These are used to provide adsorption of gases and vapors, most commonly to remove odors from extracts from kitchens or industrial processes. An efficiency of 95 per cent is obtainable and the carbon has a long life since heating can reactivate it. 

The adsorption of gases on solid surfaces proceeds to such an extent that approximately 10 7 gr. is present per cm.2 in the equilibrium state. This is of the same order of magnitude as the strength of the limiting capillary layer of a liquid ( 184), hence it is not improbable, as suggested by Faraday (9) (1884), that the adsorbed gas is sometimes present in the liquid state. The adsorbed amount increases with the pressure and diminishes with rise of temperature. The first effect does not follow a law of simple proportionality, as in the case of the absorption of gases by liquids, rather the adsorbed amount does not increase so rapidly, and the equation ... 

In considering the adsorption of gases on solid surfaces we will suppose that m gr. adsorbent take up x c.c. gas, reduced to N.T.P. Then, since the solid adsorbent has a spongy structure,... 

It was observed by de Saussure in 1814 that heat is evolved during the adsorption of gases on charcoal, and quantitative measurements were made by Favre (24) (1874), Chappuis (1888), and Dewar (25) (1904). 

Adsorption of Gases on Surfaces Modified by Alkali Promoters... 

Most studies of the effect of alkalis on the adsorption of gases on catalyst surfaces refer to CO, NO, C02, 02, H2 and N2, due to the importance of these adsorbates for numerous industrial catalytic processes (e.g. N2 adsorption in NH3 synthesis, NO reduction by CO). Thus emphasis will be given on the interaction of these molecules with alkali-modified surfaces, especially transition metal surfaces, aiming to the identification of common characteristics and general trends. 

W. Rudinski, and D.H. Everett, Adsorption of gases on heterogeneous surfaces, Academic Press, London (1992). 

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