STEADY AND UNSTEADY CO OXIDATION ON PLATINUM WITH ALLOWANCE FOR EXTERNAL DIFFUSION RETARDATION

A mathematical model for catalytic oxidation of CO on a spherical plat inum catalyst with allowance for the influence of gas diffusion is dev eloped and studied. The model explains the origin of the effects of bi furcation and oscillation of a steady reaction rate. The model is base d on the four-stage catalytic Elley-Ridley mechanism. In contrast to t he case where gas diffusion retardation is ignored and only one basic form of catalyst phase plane exists, owing to the consideration of the effect of gas diffusion, we found two additional regimes of catalyst operation. These additional regimes make it possible to explain the or igin of the effects of bifurcation and oscillation of the steady react ion rate by which the reaction rate for a steady-state surface is mean t. When the surface concentrations of adsorbing reagents or free catal ytic sites vary in the course of the reaction, the regime of catalyst operation is called unsteady. The reaction rate when the catalyst reac hes a steady state is determined for all possible regimes of catalyst operation. Based on analysis of the results obtained, we give some pra ctical recommendations on an increase in. the reaction rate. The hyste resis of the reaction rate is explained.