Cold Start Performance and Enhanced Thermal Durability of Vanadium SCR Catalysts 2009-01-0625

For diesel applications, cold start accounts for a large amount of the total NO_x emissions during a typical Federal Test Procedure (FTP) for light-duty vehicles and is a key focus for reducing NO_x emissions. A common form of diesel NO_x aftertreatment is selective catalytic reduction (SCR) technology. For cold start NO_x improvement, the SCR catalyst would be best located as the first catalyst in the aftertreatment system; however, engine-out hydrocarbons and no diesel oxidation catalyst (DOC) upstream to generate an exotherm for desulfation can result in degraded SCR catalyst performance. Recent advances in vanadia-based SCR (V-SCR) catalyst technology have shown better low temperature NO_x performance and improved thermal durability. Three V-SCR technologies were tested for their thermal durability and low-temperature NO_x performance, and after 600°C aging, one technology showed low-temperature performance on par with state-of-the-art copper-zeolite SCR (Cu-SCR) technology. This V-SCR catalyst was further compared with the Cu-SCR technology for hydrocarbon tolerance, sulfur tolerance, and ammonia storage capacity. The V-SCR technology had similar hydrocarbon tolerance, superior sulfur tolerance, and less ammonia storage than the Cu-SCR catalyst.