We propose a low-dimensional model of the three-way catalytic converter (TWC) that would be appropriate for real-time fueling control and TWC diagnostics in automotive applications. The model reduction is achieved by approximating the transverse gradients using multiple concentration modes and the concepts of internal and external mass transfer coefficients, spatial averaging over the axial length and simplified chemistry by lumping the oxidants and the reductants. The reduced order model consists of seven ordinary differential equations and captures the essential features of a TWC providing estimates of the oxidant and reductant emissions, fractional oxidation state (FOS) and total oxygen storage capacity (TOSC). The model performance is tested and validated using data on actual vehicle emissions resulting in good agreement for both green and aged catalysts including cold-start performance. We also propose a simple catalyst aging model that can be used to update the oxygen storage capacity in real time so as to capture the change in the kinetic parameters with aging. Catalyst aging is accounted via the update of a single scalar parameter in the model. The computational efficiency and the ability of the model to predict FOS and TOSC make it a novel tool for real-time fueling control to minimize emissions and diagnostics of catalyst aging. (C) 2012 Elsevier Ltd. All rights reserved.