Sulfur Tolerance and DeSOx Studies on Diesel SCR Catalysts

Base metal/zeolite catalysts, particularly containing copper and iron, are among the leading candidates for treatment of NOx emissions for diesel applications. Even with the use of ultra low sulfur fuel, sulfur poisoning is still a durability issue for base metal/zeolite SCR catalysts. In this study, the impact of sulfur poisoning on SCR activity and the stored sulfur removal effectiveness were investigated on several Cu and Fe/zeolite SCR catalysts after different thermal aging. The impact of sulfur was more significant on the Cu than on Fe/zeolite SCR catalysts for the NOx activity. It was found that the sensitivity of thermal aging status to the sulfur poisoning impact was different. The impact of sulfur on NOx activity changed with thermal aging on some catalysts, while it remained relatively the same for other catalysts. The most thermally durable SCR catalyst was not necessarily the most durable to sulfur poisoning. These results suggested that each base metal/zeolite SCR catalyst has its own characteristic response to sulfur poisoning. Control of sulfur poisoning and strategy for deSOx might be different depending on the formulation as well as thermal aging status. This study provides a better estimate of the durability of SCR catalysts as well as the strategy of deSOx for diesel engine aftertreatment.