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It has long been recognized that the key to achieving stringent emission standards such as ULEV is the control of cold-start hydrocarbons. This paper describes a new approach for achieving excellent cold-start hydrocarbon control. The most important component in the system is a catalyst that is highly active at ambient temperature for the exothermic CO oxidation reaction in an exhaust stream under net lean conditions. This catalyst has positive order kinetics with respect to CO for CO oxidation. Thus, as the concentration of CO in the exhaust is increased, the rate of this reaction is increased, resulting in a faster temperature rise over the catalyst.

The use of hydrocarbon traps to reduce cold-start emissions is one of the numerous methods that have been suggested to meet ULEV hydrocarbon emission requirements. To aid in our understanding of hydrocarbon traps and in the design of improved hydrocarbon trap systems, in-situ mass spectrometry has been used to speciate several hydrocarbons during the first 505 seconds of an FTP from the exhaust of a 2.0 L vehicle fitted with hydrocarbon traps in the after treatment system. This technique allows second-by-second engine-out and vehicle-out hydrocarbon speciation. The in-situ mass specrometry technique has shown that hydrocarbon traps are generally effective for trapping aromatics and C4+ alkanes and alkenes, but are ineffective in trapping methane, ethane, and ethene: Further improvements in the trapping performance for C3-C5 hydrocarbons can be made by placing a water trap in front of the hydrocarbon trap.