The dynamic behavior of a Pt-Rh/CeO2-Al2O3 three-way catalyst (TWC) under pulsed flow operation conditions (intermittent mode), such as occur in a newly developed hybrid drive system, has been studied experimentally in a laboratory apparatus with simulated exhaust gas. The parallel hybrid system is based on the combination of an Otto-cycle engine with an electric motor and a flywheel providing a short-term energy storage. This configu ration permits intermittent charging of the flywheel by the combustion engine which runs only during about 10% of the driving time. Each exhaust gas pulse (duration typically ca. 3 s) is preceded by an air pulse, which results from the filling of the engine cylinders with air at start up and shut off. Experimental studies indicated that the air pulses have a negative impact on the performance of the catalytic converter, reducing the inherent benefits resulting from the intermittent operation mode of the combustion engine. Forced asymmetric lambda-cycling during exhaust pulses was found to be most beneficial for improving catalyst performance. A simple reduced kinetic model derived from a Langmuir-Hinshelwood model for CO oxidation, which was extended by introducing CO and O-2 equivalents to mimic the complex exhaust gas, was used to describe the dynamic behavior of the TWC, The model proved to be useful for finding the optimal lambda-cycling conditions. Experiments with a real Otto-cycle engine exhaust proved that the reduced kinetic model is suitable for use in a closed loop lambda-control.