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The noble metal palladium (Pd) has the capability of simultaneously converting significant quantities of HC, CO and NOx in automotive exhaust. Primary interests in using palladium-containing TWC catalysts are overall noble metal cost reduction, reduction in rhodium usage and important performance advantages. Dynamometer aging experiments comparing palladium and platinum/rhodium catalysts were conducted under a variety of operating conditions. Vehicle evaluation of these aged catalysts under U.S. FTP-75, European ECE-15 and Japan 10-Mode conditions indicate that palladium-only TWC technology is viable for achieving high levels of three-way control. Vehicle aging studies (25K miles) were also conducted. They confirm the excellent durability results obtained from the dynamometer aging studies: the palladium-only TWC catalyst gave essentially equivalent U.S. FTP-75 and Japan 10-Mode performance to a high-tech platinum/rhodium catalyst.

The performance data for monolithic ceramic converters, to date, shows that fuel management, engine characteristics, substrate design, catalyst formulation, substrate/coating interaction, and packaging design have a profound influence on converter durability and sustained activity and that certain trade-offs are necessary to optimize the overall performance of the converter system. This paper concentrates on the effect of the catalyst system on light-off performance, steady state conversion efficiency, pressure drop, high temperature strength, and thermal shock resistance. The physical properties and engine test data for Corning's EX-20, 400/6 square cell substrate with two different catalyst formulations, production high-tech vs advanced high-tech, show that the advanced catalyst results in marked improvement in mechanical durability and catalytic activity over that achievable with the production catalyst due to improved substrate/coating interaction.

An H2S odor problem has appeared for certain vehicles fitted with modern three-way catalysts. A sulfur storage/H2s release mechanism is proposed as a source of the odor problem. The effects of various operating parameters on the release of H2S are presented. Two methods of modifying three-way catalysts to minimize H2S release while maintaining good catalyst performance and high temperature durability are demonstrated.

Durability performance characteristics of copper-containing base metal catalysts and base metal/low noble metal catalysts have been determined in laboratory and engine aging conditions under well controlled stoichiometric closed-loop A/F operation. Cu-Cr base metal formulations yield significant HC and CO conversions under stoichiometric operation after aging at 620°C, but deteriorate rapidly at high-temperature (750°C inlet) stoichiometric operation. Incorporation of Rh into the base metal formulation substantially improved NOx performance, a major weakness of base metal catalysts. The addition of Cu-Cr base metals substantially improves CO oxidation over Pt, Pd, and Rh catalysts but was accompanied by some loss of HC conversion over Pt and Rh. A Cu-Cr/Pd catalyst, however, also had better HC conversions as well as significantly improved light-off performance when compared to a Pd-only catalyst.