In recent years, automobile exhaust gas regulations have been progressing in various countries around the world, and the European Commission has announced Euro 7(1). In Euro 6(2), the CO emission limit was 1000 mg/km, but in Euro 7, the limit has been tightened to 500 mg/km. As shown above, the tightening of exhaust gas regulations, the reduction in the size of automobile parts due to the sale of cheaper automobiles and the shift to HEVs, catalysts need to be downsized. In order to downsize catalysts, catalysts with higher conversion performance need to be developed. When focusing on the catalyst conversion performance during actual driving of an automobile, it was confirmed that the subsequent catalyst conversion performance tends to deteriorate when the variation in the air-fuel ratio due to driving conditions such as fuel cutoff and lean/rich mixture concentration is added to the exhaust gas. It is thought that the deterioration of conversion performance is caused by changes in the surface state of active platinum group metals, which affect the subsequent conversion performance. We clarified the effect of the surface state of active platinum group metals on the conversion rate, and experimentally investigated engine control methods, mainly perturbation control methods, to recover from a deteriorated catalyst state.
Kishimoto et al. (Wed,) studied this question.