Heat‐ and mass‐transfer induced hysteresis effects during catalyst light‐off testing

Abstract

The physical and chemical phenomena responsible for hysteresis effects met in lab testing of automotive catalysts under transient temperature conditions are investigated. The hysteresis, which is identified by the difference in light‐off temperatures between temperature increase/decrease modes, could be important for model calibration purposes and revealing for some of the processes occurring within the reactor. With the help of mathematical modelling, we investigate the main parameters affecting the magnitude of the hysteresis and attempt to derive conclusions of practical relevance. We demonstrate that the hysteresis effect is closely linked to the active reaction zone length. The importance of internal species diffusion resistance in the washcoat, which is sometimes neglected for simplicity, is highlighted as an important factor in this context. On the basis of a sensitivity analysis, we identify the potential pitfalls that may occur during practical model calibration procedures on the basis of light‐off tests.