Simulations of anisotropic front propagation in the H2+O2 reaction on a Rh(110) surface

A mathematical model is presented which reproduces the experimental results of anisotropic front propagation in the bistable H-2+O-2 reaction on a Rh(110) surface. A model represented by a system of two coupled nonlinear reaction-diffusion equations incorporates the chemical diffusion of adsorbed hydrogen and oxygen. In previous experiments with a photoelectron emission microscope (PEEM) it had been demonstrated that in the system H-2+O-2/Rh(110) the front anisotropy varied strongly with the experimental parameters. Depending upon temperature and hydrogen partial pressure the reaction fronts were elongated in the [<1(1)over bar>0]-direction or in the [001]-direction of Rh(110). Key features of the mathematical model are diffusion of hydrogen and oxygen and the strong inhibitory site-blocking effect of adsorbed oxygen on the adsorption and diffusion of hydrogen. The model reproduces well the experimental data concerning the bistability range, the dependence of the front propagation velocity on the hydrogen partial pressure and temperature, and the parameter-dependent change in front anisotropy. The simulations demonstrate that oxygen diffusion cannot be neglected despite the fact that under typical conditions the rate of oxygen diffusion is several orders-of-magnitude slower than that of hydrogen. (C) 2000 American Institute of Physics. [S0021-9606(00)71233-5].