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 pore generations, since in the intermediate domain the rate is only weakly dependent on k; such catalysts are more sensitive to deactivation of the outer pore generations.
|Number of pages||9|
|Journal||Industrial and Engineering Chemistry Research|
|State||Published - 1999|