Catalyst Strategies for Meeting Super-Ultra-Low-Emissions-Vehicle Standards

The control of emissions from mobile sources continues to play an important part in air quality improvement. Future reductions in vehicle emissions are proposed or legislated in many countries throughout the world. The most stringent of these standards under discussion are those in the Californian LEV-II proposal, a part of which is the SULEV standard which requires a large reduction in hydrocarbon emissions, together with a significant decrease in NOx, over those legislated for ULEV. This requires the engine and aftertreatment system to deliver both a substantial reduction in the emissions of hydrocarbon during engine warm-up and increased NOx conversion during high speed operation, compared to previous ULEV systems. In this paper we outline three different catalyst systems which show the potential to provide reduction in vehicle emissions below the currently legislated ULEV and European Stage IV standards. These are an Ambient Temperature Light-off Aftertreatment System that uses an advanced low temperature catalyst, an Exhaust Gas Ignition System which generates heat by ignition of the exhaust gas in front of an underfloor catalyst, and a third system which combines an electrically heated catalyst with a hydrocarbon trap. The relative advantages of these systems will be discussed.