ON THE COMPLEX STRUCTURE OF REACTION-DIFFUSION FRONTS OBSERVED DURINGCO OXIDATION ON PT(100)

In the catalytic oxidation of CO on Pt{100}, we have been able to iden tify, using small-area LEED, the different adsorbate-covered regions w hich constitute the reaction-diffusion fronts observed in photoelectro n emission microscopy. The resulting concentration profile is simulate d in one dimension with the help of a simple two-variable model derive d from the Langmuir-Hinshelwood mechanism. The characteristic features of the experiment are reproduced if it is assumed that the CO diffusi on coefficient is strongly enhanced (by a factor of 7) at coverages co rresponding to the (square-root 2 x square-root 2)R45-degrees-CO phase and reduced by surface defects.