LNT + in situ SCR catalyst system for diesel emissions control

An overview is presented of laboratory and vehicle studies conducted at Ford Motor Company on the LNT + in situ SCR catalyst approach to diesel emissions control. Specifically, the paper focuses on results obtained with so-called “2nd-generation” systems developed by Fordʹs catalyst suppliers since 2007–2008. These systems are characterized by improvements in durability, performance and cost relative to their predecessors. Key features of the 2nd-generation LNT + in situ SCR technology include: (1) lower desulfation temperatures of the LNT, (2) lower LNT platinum group metal (PGM) content than required for LNT-only systems, (3) advanced SCR catalysts of the types used in commercial zeolite-based SCR applications, (4) synergetic coupling of the LNT and SCR catalyst performance to maintain high efficiency after aging, (5) a non-ammonia NOx reduction mechanism over the SCR catalyst in addition to the standard mechanism based on ammonia storage, and (6) improved hydrocarbon oxidation efficiency owing to the SCR catalyst. Taken together, these advances improve the prospect of meeting future emission regulations on light-duty diesel vehicles, but not without considerable challenge to both the aftertreatment system and control strategy for achieving simultaneous low NOx and non-methane hydrocarbon emissions while minimizing fuel consumption.