Polanyi potential theory adsorbate molecule

The concept of a pore potential is generally accepted in gas adsorption theory to account for capillary condensation at pressures well below the expected values. Gregg and Sing ° described the intensification of the attractive forces acting on adsorbate molecules by overlapping fields from the pore wall. Adamson has pointed out that evidence exists for changes induced in liquids by capillary walls over distances in the order of a micron. The Polanyi potential theory postulates that molecules can fall into the potential field at the surface of a solid, a phenomenon which would be greatly enhanced in a narrow pore. 

Polanyi s potential theory of adsorption views the area immediately above an adsorbent s surface as containing equipotential lines which follow the contour of the surface potential. When a molecule is adsorbed it is considered trapped between the surface and the limiting equipotential plane at which the adsorption potential has fallen to zero. Figure 9.1 illustrates these equipotential planes. In the diagram, Y represents a pore and X depicts some surface impurity. 

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. 

The molar work done for moving the sorbate molecules from the ambient gas phase to the standard state of the adsorbed phase is defined as adsorption potential, A, by the Polanyi theory. The standard state of adsorbate in the adsorbed phase is a saturated liquid for the adsorption at... 

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