Physical adsorption of gases on heterogeneous surfaces. Series expansion of isotherms using central moments of the adsorption energy distribution

Abstract

An alternative approach to the use of the usual integral equation for heterogeneous adsorption is developed. It provides a means of obtaining an explicit result for arbitrary local isotherms and distributions of energy of adsorption. The approximation is compared with exact numerical integrations, using the Langmuir local isotherm and a normal energy distribution. The series fails to converge for energy distributions that are very wide. Truncation of the expansion after the first-order term yields an equation which is capable of fitting experimental isotherm data.