ADSORPTION BY NONHOMOGENEOUS POROUS SOLIDS - EFFECT OF ADSORPTION ENERGY GRADIENT ON SURFACE FLOW

There are surface diffusion processes of practical importance involving adsorbents in which the adsorption energy varies over a macroscopic distance. Pellets with nonuniform porosity are often used as catalyst supports, and at some stage of the preparation of the catalyst active components are introduced by impregnation. The penetration of the impregnating solute and the resulting distribution in the pellet is affected by the variation of the adsorption energy along the diffusion path, which should be taken into account in the derivation of kinetic models. It is shown that when one considers diffusion in pellets with nonuniform porosity, Fick's equation in its simple form can be inadequate and more realistic modeling can be achieved by taking into account heterogeneity.