Validity of the two-dimensional approximation to the description of gas adsorption on solids

The first two pseudo-planar and two-dimensional virial coefficients are compared. Expressions for three-dimensional pseudo-planar virial coefficients resulting from our theory of virial expansions for adsorption isotherms are compared with those resulting from the gas–solid virial theory. Explicit results are given for the Lennard-Jones (12,6) and (9,3) potentials, hard-sphere and Lennard-Jones (9,3) potentials and for the square-well potentials with different energies for the gas–gas and gas–solid interactions.