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Selective catalytic reduction (SCR) of NOx by NH3 is under intensive development as a technology to enable diesel engines to meet stringent NOx emission regulations. Cu/zeolite SCR catalysts are leading candidates because of their ability to catalyze NOx reduction at the low temperatures encountered on many diesel vehicles. However, both engine evaluation and laboratory studies indicated that commonly available Cu/zeolite SCR catalysts did not have sufficient thermal stability to maintain performance during the full useful life of a vehicle (with steady-state NOx conversion decreasing ~ 10% over 64 hours of hydrothermal aging at 670 °C). Characterization of aged Cu/zeolite catalysts revealed that the loss of zeolite acidity was the main deactivation mechanism; while the zeolite support maintained its framework structure and surface area after aging. Improvement of the hydrothermal stability of the acid sites resulted in a new generation of SCR catalysts.

FTP hydrocarbon emissions were measured on a sport utility vehicle comparing two catalyst systems. One system consisted of a close-coupled three-way catalyst and an underbody catalyst-only version of a hydrocarbon trap catalyst. The other system consisted of the same closed-coupled catalyst and underbody hydrocarbon trap catalysts. Thus, these systems compared a non-hydrocarbon trap system and a hydrocarbon trap catalyst system. Fresh and 50-hour aged testing showed that the hydrocarbon emissions were approximately 10% lower for the hydrocarbon trap catalyst system. When an air pump was used to inject air into the exhaust system, the hydrocarbon emissions of the hydrocarbon trap catalyst system were approximately 20% lower than the non-trap system. Hydrocarbon speciation demonstrated that the magnitude of the benefit of the hydrocarbon trap catalyst system was related to the characterization of the blend of hydrocarbon species in the exhaust after the close-coupled catalysts.

As one method of meeting current and future emission regulations on vehicles, automakers have increased PGM loadings in three-way catalysts. Engine dynamometer and FTP testing after accelerated engine agings were performed to compare current Pd:Rh and Pt:Rh catalysts with new Pd:Rh and Pt:Rh catalysts. This comparison demonstrated that enhanced three way performance can be obtained in the new catalysts with reduced Pd loadings or with the use of Pt:Rh instead of Pd:Rh. These improved catalysts will reduce the demand for high PGM loadings as well as provide flexibility in the PGM combinations used in exhaust systems.

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.