Sulfur Management of NOx Adsorber Technology for Diesel Light-duty Vehicle and Truck Applications 2003-01-3245

Sulfur poisoning from engine fuel and lube is one of the most recognizable degradation mechanisms of a NO_x adsorber catalyst system for diesel emission reduction. Even with the availability of 15 ppm sulfur diesel fuel, NO_x adsorber will be deactivated without an effective sulfur management. Two general pathways are currently being explored for sulfur management: (1) the use of a disposable SO_x trap that can be replaced or rejuvenated offline periodically, and (2) the use of diesel fuel injection in the exhaust and high temperature de-sulfation approach to remove the sulfur poisons to recover the NO_x trapping efficiency. The major concern of the de-sulfation process is the many prolonged high temperature rich cycles that catalyst will encounter during its useful life. It is shown that NO_x adsorber catalyst suffers some loss of its trapping capacity upon high temperature lean-rich exposure. With the use of a disposable SO_x trap to remove large portion of the sulfur poisons from the exhaust, the NO_x adsorber catalyst can be protected and the numbers of de-sulfation events can be greatly reduced.

Spectroscopic techniques, such as DRIFTS and Raman, have been used to monitor the underlying chemical reactions during NO_x trapping/regeneration and de-sulfation periods, and provide a fundamental understanding of NO_x storage capacity and catalyst degradation mechanism using model catalysts. This paper examines the sulfur effect on two model NO_x adsorber catalysts. The chemistry of SO_x/base metal oxides and the sulfation product pathways and their corresponding spectroscopic data are discussed.