SPATIOTEMPORAL PATTERNS IN A HETEROGENEOUS MODEL OF A CATALYST PARTICLE

A novel problem, of diffusion resistance in porous particles that cata lyze kinetically unstable reactions, is introduced, analyzed and simul ated in order to unveil the possible spatiotemporal patterns in the di rection perpendicular to the surface. Pore-diffusion resistance is a c ore problem in chemical reaction engineering. The present problem is d escribed mathematically by three variables: a very-fast and long-range d pore-phase concentration, a fast and diffusing autocatalytic surface species (activator) and a slow and localized surface activity. Unlike homogeneous models of pore disfussion resistance, in which instabilit ies emerge only with strong diffusion resistance, the present model ex hibits oscillatory or excitable behavior even in the absence of that r esistance. Patterns are generated by self-imposed concentration gradie nts. A detailed kinetic model of a simple but reasonable reaction mech anism is analyzed, but the qualitative results are expected to hold in other similar kinetics. The catalyst particle is a three-dimensional system and it may exhibit symmetry-breaking in the directions parallel to the surface due to interaction between the fast diffusion of a flu id-phase reactant and the slow solid-phase diffusivity of the activato r. A thin catalyst can be described then by a one-dimensional reaction -diffusion system that admits patterned solutions. We point our this p ossibility, but refer to another work that investigates such patterns in the general framework of patterns due to interaction of surface rea ction and diffusion with gas-phase diffusion and convection. (C) 1996 American Institute of Physics.