The objective of this stud), was to prepare zeolite-based monoliths (Cu/ZSM-5 on cordierite), to test their catalytic activity in the direct decomposition of nitrogen monoxide and to develop mathematical model of the monolith reactor. Reaction of NO decomposition was performed over the monolith catalysts with various thickness of the catalytic washcoat, in temperature range from 573 to 773 K, under atmospheric pressure and at various space times. Two-dimensional heterogeneous model is applied to describe a single channel of the monolith reactor. Langmuir-Hinshelwood type of kinetic model is considered. The influence of both inter- and intraphase diffusion on the performance of the monolith reactor is quantitatively described by means of the governing effectiveness factors. The mean and local gas-solid mass transfer coefficients are derived from the concentration gradients using the proposed model. The proposed model is verified by comparing computer simulation data with experimental laboratory results. (C) 2003 Elsevier B.V. All rights reserved.