Experimental Evaluation of Reformate-Assisted Diesel NOx Trap Desulfation 2005-01-3878
NOx adsorber catalysts are leading candidates for improving NOx aftertreatment in diesel exhaust. The major challenge in the use of adsorbers that capture NOx 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 NOx, and, since it is more stable than nitrates, inhibits the ability of the catalyst to adsorb NOx. 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 NOx 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 NOx adsorber efficiency.