Chapter 5 - Ideal Monolayer Adsorption on Heterogeneous Surfaces

Abstract

This chapter provides an overview of ideal monolayer absorption on heterogeneous surfaces. The concept of surface heterogeneity is discussed through the Henry's law constant. The Henry's law constant is the product of the temperature-dependent factor, which depends on the energy distribution function, and the monolayer capacity ( N m ). The monolayer capacity can be calculated from the experimental Henry constants. The value of N m is, for a given adsorption system, related to the degree of mobility of the adsorbed phase. If this changes, there will be associated changes in the monolayer capacity. In an analysis described in the chapter, the constancy of N m calculated at various temperatures for chosen values of w or heterogeneity parameter ( w ˆ )was assumed to be a test for the success of the model. Since surface heterogeneity affects not only the distribution of adsorption energies but also the distribution of barrier heights controlling mobility across the surface, some correlation will be expected between these two distributions. Consequently, at each temperature, the mobility will be expected to be different on different patches, and the overall mobility will be expected to vary continuously with temperature.