Dynamic Monte-Carlo simulations of diffusion limited reactions in rough nanopores

It has recently been demonstrated that self- (or tracer) diffusivities and transport diffusivities of gases in nanoporous materials may differ in the Knudsen regime, when the pore surface is rough on molecular scales: Self-diffusion is roughness dependent, while transport diffusion is not. The impact of this result on diffusion-controlled reactions, catalyzed by porous, catalysts with a rough internal surface, is now investigated. We consider the steady-state problem of a species diffusing in a three-dimensional pore with a fractal surface, on which the species reacts: Dynamic Monte-Carlo simulations and analytical calculations show that the self-diffusivity plays the fundamental role in determining the effective catalytic efficiency of a rough pore. The transport diffusivity, on the other hand, is not the fundamental quantity of interest to surface phenomena such as heterogeneous catalysis, and can only be used for porous materials with a smooth internal surface, in which case the self- and transport diffusivities coincide. (C) 2003 Elsevier Ltd. All rights reserved.