Experimental Evaluation of Reformate-Assisted Diesel NOx Trap Desulfation 2005-01-3878

NO_x adsorber catalysts are leading candidates for improving NO_x aftertreatment in diesel exhaust. The major challenge in the use of adsorbers that capture NO_x in the form of nitrates is their susceptibility to sulfur poisoning. Sulfur, which is present in diesel fuel, adsorbs and accumulates as sulfate (SO₄^-2) at the same adsorption sites as NO_x, and, since it is more stable than nitrates, inhibits the ability of the catalyst to adsorb NO_x. It is found that high temperature (> about 650 °C) in the presence of a reducing gas is required to release sulfur rapidly from the catalyst. Since the peak temperatures of diesel engine exhaust are below 400 °C, additional heat is required to remove the sulfur. This work describes a reformate-assisted “sulfur purge” method, which employs heat generated inside the NO_x trap catalyst by exothermic chemical reactions between the oxygen in diesel exhaust and injected reformate (H₂ + CO). Our results with a laboratory gas bench system show that catalyst desulfation is successful following a desulfation schedule with an inlet gas temperature of about 300 °C. In addition, we have examined impact of temperature, duration of exposure, and reformate-based gas compositions employed for rich-gas desulfation on NO_x adsorber efficiency.