A mathematical model of an automotive catalytic converter system has been developed. It consists of a one-dimensional two-phase model of the exhaust monolith and considers the spatially varying heat and mass transfer between gas and wall at the monolith entrance. The reaction kinetics used are based upon measurements with CO, propene, propane and water vapour as key components. In a joint research project with Volkswagen AG, the model has been used to study the improvement of the cold start behaviour using an electrically heated pre-catalyst (EHC). The results of a systematic simulation study of all relevant geometrical parameters and of the appropriate heating strategy are presented. The results obtained have been verified in practical operation and have contributed to a new design of electrically heated precatalysts.