(511g) Effects of Fuel Type On Dual SCR Aftertreatment

Low-cost NOx aftertreatment is one of the main challenges facing high efficiency diesel engines and gasoline engines operating under lean conditions. In addition, the global demand for alternative fuels has sparked a renewed interest in catalyst systems that can effectively reduce NOx emissions from engines using a range of normal and bio-based HC fuels. Until recently, most approaches have relied on precious metals to either store NOx and subsequently release and reduce it under rich conditions (lean NOx traps), or they use NH₃-SCR catalysts with urea injection to reduce the NOx under lean conditions. However, we have introduced a multi-component Dual SCR aftertreatment system that is capable of obtaining NOx reduction efficiencies from 80% to 95% under lean conditions, without the use of precious metals or urea injection into the exhaust. The Dual SCR approach here uses an Ag HC-SCR catalyst followed by an NH₃-SCR catalyst and has been tested in bench reactors and in a single-cylinder engine test cell with the Dual SCR aftertreatment system. In bench reactor studies from 150 C to 500 C, we have found, for modest C/N ratios, that NOx reacts over the first catalyst to predominantly form nitrogen. In addition, it also forms ammonia in sufficient quantities to react on the second NH₃-SCR catalyst to improve system performance. The operational window and the formation of NH₃ are improved in the presence of small quantities of hydrogen (0.1-1.0%). A range of fuels, including E85 and diesel were used as reductants. This non-urea lean NOx reduction system has, at a fraction of the catalyst cost of a precious metal system, shown very high NOx reduction activity over a broad range of temperature and feed conditions, using several fossil and bio-based fuels injected into the exhaust. In both bench and engine testing the ammonia production has been measured after the initial catalyst and is found to be highest for alcohol-containing fuel reductants. Dual SCR technology could be a key enabler for low cost and efficient NOx reduction to help auto manufacturers meet Tier2/Bin5 and Tier2/Bin2 emissions standards.