Selectivity and Deactivation of Diffusion-Limited Reactions in a Pore-Fractal Catalyst

Abstract

One of the main results of studies into reaction and diffusion in a pore-fractal “catalyst” is the existence of an intermediate low-slope asymptote, in the plot of log(rate) vs log k, which separates the known asymptotes of kinetics- and diffusion-controlled rates. In that domain the fractal catalyst is more active than a catalyst of uniform pores having similar average properties. Here we consider the selectivity and deactivation processes in pore−fractals such as the Sierpinski gasket or a simple pore tree, using numerical or approximate solutions, respectively. The selectivity, in a system of a fast and slow simultaneous reactions, can be markedly different than that in a uniform-pore catalyst. Specifically, slow undesired reactions of higher order can be effectively suppressed in such a system. Three mechanisms of deactivation are considered and are characterized by curves of rate vs average activity: Pore-fractal catalysts are less sensitive to uniform deactivation or to deactivation of the inner po...