The Potential Theory of Adsorption

In developing his later views on the social practice of science, Polanyi explicitly drew upon his earlier career experiences in the 1920s and 1930s. Two series of investigations at the boundaries of chemistry and physics were prominent among his examples of scientific practice and the distribution of merit within the scientific community. I turn now to these two cases the potential theory of adsorption on solid surfaces and X-ray studies of the solid state. 

Polanyi, The potential theory of adsorption," 1013, n. 2. Polanyi noted that Arnold T. Eucken had introduced the term Ad-sorptionspotential in 1914, a few months before Polanyi s first paper on the subject. 

Polanyi, The potential theory of adsorption, 1010. The chemist Hermann F. 

A major development in understanding the adsorption of gases and vapors on microporous carbons was provided by the potential theory of adsorption by Polanyi. This theory assumes that, on the adsorbent surface, the gas molecules are compressed by attractive forces acting between the surface and the molecules, and these forces decrease with the increasing distance from the surface. The force of attraction at any given point near the surface is measured by the adsorption potential (A), which can be defined as the work done to transfer a molecule from the gas phase to a given point above the surface. 

Dubinin MM. The potential theory of adsorption of gases and vapors for adsorbents with energetically nonuniform surfaces. Chem. Rev., 1960 60 235-241. 

Polanyi, M., Discussion of the Potential Theory of Adsorption in Adsorption of Gases and Vapors, by Stephen Brunauer, Princeton University Press, Princeton, N. J., 1947. 

The potential theory of adsorption was introduced by Polanyi in 1914. Dubinin [48,49] and Stoeckli et al. [50] improved the theory and termed it the theory of volume filling of micropores (TVFM). This theory has been widely used in correlating the effect of temperature on the adsorption isotherms of pure gases. The modern formulationof TVFM is the Dubinin-Astakhov (DA) equation, which is expressed as... 

The potential theory of adsorption first introduced in 1914 by Polanyi" " and later modified by Dubinin for adsorption on microporous adsorbents is still regarded as fundamentally sound and accepted as correct and better than all the other theories. This longevity of the theory is due to its essentially thermodynamic character and lack of insistence on a detailed physical picture. 

Adsorption theory of the volume filing of micropores (TVFM theory) has been proposed by Dubinin and Radushkievich [136], but this approach has originated from the potential theory of adsorption introduced by Eucken [112] and Polanyi [113,114]. 

Experimental verification of the Polanyi theory deals with the calculation of the characteristic adsorption curve by means of an experimental isotherm and hence determination of the isotherms at different temperatures. The first practical examinations of the potential theory of adsorption carried out by Titoff [137] and Berenyi [138] showed the good agreement with experiment. 

Introduction of heterogeneity indicates insufficiency of the straightforward thermodynamic approach based on common equations of state to express the specificity of interactions between the adsorbed phase and the adsorbent. The two new physical ideas behind Eq. (45) are localization of the adsorbed molecules at different points of the surface (patches) and a possibility of dijferent energetic interaction of the molecules with the surface. These ideas have been developed in a different way in the two other thermodynamic concepts of adsorption the localized approach and the potential theory of adsorption. 

An alternative to the localized theory of adsorption is the so-called potential theory, which has been developed as a slab adsorption theory on a surface and its analog for adsorption in microporous media, the theory of volume filling in micropores (TVFM). The potential theory of adsorption, first formulated by Polanyi [91], is widely used for the description of adsorption of gases on a solid. The TVFM is applied to adsorption in activated carbons, silica gels, and other types of microporous medium. 

The described properties of the potential theory of adsorption make it preferential to the theory of localized adsorption, at least, for complex thermodynamic conditions. On the other hand, the potential theory incorporates specific physical information about the phenomenon of adsorption, which is absent in the general thermodynamic approach. A major disadvantage of the multicomponent potential theory is the computational difficulties arising in the calculation of the multicomponent segregation in the external field. This is the reason why the development of this theory has been delayed until our recent works [92-94]. The development of modem methods of computational thermodynamics [68] has made it possible to perform these calculations quite efficiently. 

An alternative approach to lAST/RAST which combines a thermodynamic treatment with a specific consideration of fluid-solid interactions is the potential theory of adsorption (Polanyi (1914)-Dubinin (1950)), especially in the form designed for multi-component mixtures pioneered by Shapiro and Stenby (1998). 

Equation (7.24) is of fundamental importance in surface sdence. It rdates interfadal forces with the adsorption of a vapor to a solid surface. The concept goes back to Michael Polanyi and it is known as the potential theory of adsorption [802]. The basic idea is that vapor molecules close to a surface feel a potential-similar to the gravitation field of the earth. The potential isothermally compresses the gas dose to the surface. Once the pressure becomes higher than the equilibrium vapor pressure, it condenses and forms a liquid film. 

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