Theory of localized and nonlocalized adsorption of gases on heterogeneous surfaces

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Abstract
A theory is developed for adsorption of gases on patchwise heterogeneous surfaces with the assumption of a discrete distribution of site energies. The lateral interactions between adatoms in the first layer are neglected, but those in the second layer are accounted by the cluster expansion theorem. The heterogeneity effect on the isotherm is studied via the renormalization of the first layer coverage. The representation of the first layer coverage in the form of a padé approximant is introduced to determine the distribution of site energies. There is established a set of inequalities for the coefficients of the Padé approximant, which is essential in the analysis of experimental data. The theory is successfully applied to the systems of gases adsorbed on rutile reported by Drain and Morrison. It is found that the rutile surface primarily consists of three kinds of patches, the relative extent of which is proportional to that of cleavage planes of rutile. The distribution of site energies is discussed in comparison with the distribution functions previously obtained by other authors. The cluster integrals for the second layer are determined. The theory is also applied to the systems of gases on porous silver given by Hobson.

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