Steady and unsteady co oxidation on platinum with allowance for external diffusion retardation

A mathematical model for catalytic oxidation of CO on a spherical platinum catalyst with allowance for the influence of gas diffusion is developed and studied. The model explains the origin of the effects of bifurcation and oscillation of a steady reaction rate. The model is based on the four-stage catalytic Elley-Ridley mechanism. In contrast to the 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 origin of the effects of bifurcation and oscillation of the steady reaction rate by which the reaction rate for a steady-state surface is meant. When the surface concentrations of adsorbing reagents or free catalytic sites vary in the course of the reaction, the regime of catalyst operation is called unsteady. The reaction rate when the catalyst reaches a steady state is determined for all possible regimes of catalyst operation. Based on analysis of the results obtained, we give some practical recommendations on an increase in the reaction rate. The hysteresis of the reaction rate is explained.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 6, pp. 52–61, November–December, 1996.