A numerical study of transient, compressible, reacting flow inside an adiabatic catalytic converter is carried out with the one–dimensional model. The important physical/chemical phenomena existing in the catalyzed monolith are included in the model. The effects of the time dependent inlet mass flow rate and some important geometrical parameters on the gas/solid phase temperatures along the converter and the conversion efficiency are investigated. Results show that the monolith (wall) temperature along the converter, the maximum monolith temperature, the location of the reaction front, and the conversion efficiency are affected by time dependent fluctuations of the inlet mass flow rate. In addition, the converter characteristics and the conversion efficiency are very sensitive to the geometrical parameters (such as the cell density, the void fraction, and the wall thickness).