Mathematical modeling of the influence of oxygen mobility in solid catalyst on transient regimes of catalytic reaction has been carried out. The region of Thiele modulus Psi in which the diffusion of oxygen in solid catalyst effect on the transient regime of reaction was determined. These values of tP lies in the interval of 0.7-7. The diffusion coefficient corresponding to these values of Thiele modulus lies in the interval of 10(-17)10(-1)1 cm(2)/s. circle dot 2004 Elsevier B.V. All rights reserved.