Numerical simulation of deactivation process of three-way catalytic converters

摘要

This paper presents the numerical simulation method to predict the deactivation process of three-way catalytic converters. Three-way catalytic converter's deactivation typically results from thermal and chemical mechanisms. The major factor of thermal deactivation is the sintering of noble metal particles, which is known to depend on the aging temperature and the oxygen concentration in the exhaust gas. The chemical deactivation is mainly caused by the poisoning, which has two effects on the catalyst deactivation. One effect is the loss of the catalyst activity, which is expressed by reduced frequency factors of reaction rates. Another effect is the suppression of the noble metal sintering. Poison deposits prevent the noble metal particles from moving in the washcoat, assisted by the reduced thermal loading of reaction heats, which is caused by the loss of the catalyst activity. Modeling these deactivation factors, we propose the rate expression of noble metal sintering. The changing process of noble metal particle size and catalyst activity distributions with mileage is simulated by the procedure to predict the deactivation process. This procedure adopts above sintering rate expression, and the details are presented in this paper. Based on simulated results of the deactivated state inside the bench aged catalyst, which are noble metal particle size and catalyst activity distributions, thermal responses and light-off behaviors during warm-up tests are predicted. Predicted results show good agreement with the measured results. Moreover, transient conversion behaviors of the bench aged catalyst during LA#4 mode test are predicted. Predicted results lead to the conclusion that the numerical simulation method presented enables the prediction of the relative values of cumulated emissions of aged catalysts with sufficient accuracy.