A detailed reaction kinetic model to predict the activity of the commercial three-way catalyst (TWC), particularly 4k miles aged catalyst in an engine dynamometer, has been developed by considering all possible reactions in the catalytic converter based upon the Langmuir-Hinshelwood mechanism. The model predictions adequately describe the general trend of the measured conversions of CO, C3H6, NO and H-2 center dot NH3 and N2O formed during the reaction can also be predicted by the model. Moreover, the decrease in activity of the 100k miles aged catalyst can be well described by the model developed in the present study. (c) 2007 Elsevier Ltd. All rights reserved.