Development of a Desulfurization Strategy for a NOx Adsorber Catalyst System 2001-01-0510

The aggressive reduction of future diesel engine NO_x 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 NO_x have been the subject of many investigations. One of these systems is the NO_x adsorber catalyst, which has shown high NO_x conversion rates during previous investigations with acceptable fuel consumption penalties. In addition, the NO_x adsorber catalyst does not require a secondary on-board reductant.

However, the NO_x adsorber catalyst also represents the most sulfur sensitive emissions control device currently under investigation for advanced NO_x 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 NO_x conversion capability of a NO_x 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.