The aggressive reduction of future diesel engine NOx emission limits forces the heavy- and light-duty diesel engine manufacturers to develop means to comply with stringent legislation. As a result, different exhaust emission control technologies applicable to NOx have been the subject of many investigations. One of these systems is the NOx adsorber catalyst, which has shown high NOx conversion rates during previous investigations with acceptable fuel consumption penalties. In addition, the NOx adsorber catalyst does not require a secondary on-board reductant.
However, the NOx adsorber catalyst also represents the most sulfur sensitive emissions control device currently under investigation for advanced NOx control. To remove the sulfur introduced into the system through the diesel fuel and stored on the catalyst sites during operation, specific regeneration strategies and boundary conditions were investigated and developed. To achieve the required exhaust temperature under slightly rich conditions, a pre-catalyst may be required. Under constant engine operating conditions, the duration of the desulfurization process was varied to determine the required desulfurization period. In addition, the catalysts were aged and periodically desulfurized to determine the influence of multiple desulfurization events on long-term catalyst performance.
The test results show that using a pre-catalyst, the NOx conversion capability of a NOx adsorber catalyst can be restored even after multiple desulfurizations. However, a decline in conversion efficiency can be observed over time. In anticipation of future catalyst improvements, it can be concluded, that the adsorber catalyst is a promising technology for future vehicle applications.