In this paper the dynamics of hydrocarbons deep oxidation in. the catalyst pellet with account of intraparticle diffusion limitations under alternating adsorption stage and oxidation one is studied by means of mathematical modeling. As an example the isopropyl benzene oxidation by oxygen on Cu/Cr/Al oxide catalyst is considered. It is shown that intraparticle diffusion limitation significantly influence both adsorption and oxidation performance. The modeling results demonstrate the existence of the optimal catalyst pellet size, providing the maximum purification efficiency in the adsorption-catalytic process of VOC abatement.