OXYGEN RECOMBINATION ON A CATALYTIC SPHERE IN THE CONTINUUM-FREE MOLECULE TRANSITION

In the study of simple surface catalyzed gas reactions, the effect of reactant transport limitations on the observed kinetics may be reduced and, in fact, calibrated out of the experiment by reduction of the system pressure; However, even for mild catalysts, it is found that this must be done to a point at which the continuum concept of reactant transport becomes suspect. In order to assess this aspect, both continuum and rarefied spherical catalytic probe theories are developed and are shown to produce identical results as regards the reactant flux to the surface, although the spatial distribution of reactant is considerably different for the two cases. Analytical solutions are obtained for the rarefied case by matching inner and outer solutions in a manner proposed by Lees. Comparison of theory with experiments, conducted in a slow-flow glow discharge facility that produces some atomic oxygen which then recombines on silver-coated thermistor spheres, shows excellent agreement. (Author)