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Sulfur compounds in diesel exhaust diminish the performance of aftertreatment devices and contribute to particulate matter mass and composition. Sulfur sorbate catalysts that store and release sulfur compounds have been used in conjunction with NOx aftertreatment catalysts to decrease the negative effects of sulfur.1 The temperature range of diesel exhaust is broad and may vary with application. The effect of temperature on the performance of sulfur catalysts will determine the usefulness of such catalysts for diesel applications. In this study bench reactor and engine testing of sulfur sorbate catalysts were performed to characterize the release of sulfur compounds as a function of temperature. Engine tests were performed on a lightduty platform with No. 2 Diesel fuel.

Sorbate or “trap” catalysts are capable of obtaining greater than 90% NOx conversion in lean exhaust over a wide range of operating temperatures. The critical limitation to sorbate catalysts is their susceptibility to sulfur poisoning, which is of particular concern in diesel applications where high sulfur levels exist and exhaust temperatures are typically too low for sulfur removal with thermal techniques. A novel catalyst formulation that exhibits sulfur-resistant characteristics is introduced here. The catalyst sorbs NOx and SO2. The NOx is reduced and released as N2, and the sorbed SO2 in the form of sulfates and sulfites is reduced and released as H2S and SO2. The catalyst also oxidizes hydrocarbons and CO. The catalyst system incorporates a dual-chamber design for efficient operation.

A two-chamber catalyst system for the aftertreatment of No. 2 Diesel exhaust is demonstrated. NOx conversion efficiencies greater than 90% were obtained over a broad range of operating temperatures and NOx levels. The system incorporates a catalyst (SCONOx™) for the removal of CO, hydrocarbons, and NOx from the exhaust stream and a sulfur catalyst (SCOSOx™) for the protection of the NOx catalyst from sulfur poisoning. Both catalysts are of sorbate or “trap” type. No. 2 Diesel and hydrogen were used as reductants. Tests of the catalysts were performed with various loads, temperatures, and NOx levels. A light-duty diesel engine with no particulate control was used for the tests. All tests were conducted using No. 2 Diesel fuel. NOx conversion decay is compared with and without sulfur catalyst protection.

A two-chamber catalyst system for the aftertreatment of No. 2 Diesel exhaust is demonstrated. NOx conversion efficiencies greater than 95% were obtained over a broad range of operating temperatures and NOx levels. The system incorporates a NOx catalyst (SCONOx™) for the removal of CO, hydrocarbons, and NOx from the exhaust stream and a SO2 catalyst (SCOSOx™) for the protection of the NOx catalyst from sulfur poisoning. Both catalysts are of sorbate or “trap” type. Hydrogen is used as the reductant and can be supplied by on-board fuel reformers. Tests of the catalysts were performed with various loads, temperatures, and NOx levels. A light-duty diesel engine with no particulate control was used for the tests. All tests were conducted using No. 2 Diesel fuel.