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Selective Catalytic Reduction (SCR) catalysts have been demonstrated as effective for controlling NOx emissions from diesel engines, maintaining high NOx conversion even after the extended high temperature exposure encountered in systems with active filter regenerations. As future diesel emission regulations are expected to be further reduced, packaging a large volume of SCR catalysts in diesel exhaust systems, along with DOC and particulate filter catalysts, will be challenging. One method to reduce the total volume of catalysts in diesel exhaust systems is to combine the SCR and DPF catalysts by coating SCR catalyst technology on particulate filters. In this work, engine evaluation of SCR coated filters has been conducted to determine the viability of the technology. Steady-state engine evaluations demonstrated that high NOx conversions can be achieved for SCR coated filters after high temperature oven aging.

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.