In this paper the optimization of a heat-integrated catalytic exhaust purification system for specific use in monovalent CNG vehicles is presented. The respective simulation results are based on a multiphase 1D model of the counter current heat exchanger with catalytic coating. For validation, stationary measurements obtained with a laboratory scale prototype are shown. Furthermore, a novel cold start approach, based on a bypass system, is introduced. As inflow conditions for the transient simulations, raw emission data from a monovalent CNG vehicle, performing a full drive cycle on a dynamometer test bench, was used. Based on this simulation setup, an optimized operation strategy of the bypass during cold start has been developed. Subsequently, the geometric parameters of the heat exchanger reactor have been refined, following an optimal design strategy. (C) 2011 Elsevier B.V. All rights reserved.