New Approximate Model for Nonlinear Adsorption and Concentration Dependent Surface Diffusion in a Single Particle

A new approximate model for nonlinear adsorption (Langmuir model) and concentration dependent surface diffusion (HIO model) in a single particle was derived, based on a parabolic concentration profile assumption for the summation of the gas and adsorbed phases. The surface diffusivity was approximated with the adsorbed phase concentration evaluated at the surface of the particle, as the average of the adsorbed phase concentration, and as the average of the first two approximations. Overall, the approximate model based on the average of the first two approximations compared the best with the exact solution for a wide variety of systems and conditions.