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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.

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.