Abstract
Diesel particulate and NO_x Reduction system (DPNR) is an effective device for clean diesel aftertreatment system. The NO_x reduction is using NO_x Storage and Reduction (NSR) mechanism. However, NSR catalyst has some issues about deterioration. Therefore, further improvement is hoped for cleaner air in the future. This paper reviews the results of our study to improve the NO_x reduction performance of NSR system. NSR catalyst performance decreases because of thermal stress and sulfur poisoning. In order to improve the thermal resistance of the catalyst, we have studied the suppression of precious metal sintering using Pt-O-Ce bond. As a result, higher catalytic activity after aging especially under lower temperature condition was obtained. On the other hand, improvement for the sulfur tolerance is one of the key technologies to keep the high NO_x conversion efficiency. The temperature uniformity of NSR catalyst on desulfurization control and the catalyst improvement are effective for higher sulfur tolerance. In addition to these suppressions of the deterioration, NO_x reduction method is also important factor. The NO_x reduction method by in-cylinder rich is effective at lower temperature, and by on-catalyst rich using exhaust diesel fuel injection is also effective at higher temperature. Therefore, this combination is a beneficial solution. As a result of these improvements, it is shown that the NSR catalyst has higher NO_x conversion efficiency of over 70% on New European Driving Cycle (NEDC) mode. Moreover, sulfur trap concept has more potential with lower Platinum Group Metal (PGM) loading thanks to improvement of thermal and sulfur tolerance.
