The Effect of Aging Temperature on Catalyst Performance of Pt/Rh and Pd/Rh TWCs

With the ever-increasing stringency of emissions regulations, automotive three-way catalysts (TWCs) require much faster light-off performance and higher warmed-up activity than before. Most automotive manufacturers are considering the adoption of close-coupled catalyst systems as a means of dealing with cold start emissions and need the catalyst to have improved thermal durability.

In this paper, a new Pd/Rh is reported to be suitable for high temperature application. Due to the recent increasing Pd metal cost, a Pt/Rh with equivalent or better TWC performance needs be developed to balance the PGM usage. A current Pt/Rh catalyst seems to possess comparable TWC performance to the new Pd/Rh catalyst when the catalysts are aged at 900°C. However, aging at a temperature higher than 900°C significantly deactivated the activity of the Pt/Rh catalyst to a point that is much worse than the Pd/Rh catalyst. For the development of a new Pt/Rh catalyst, Alumina and Ce materials were optimized to compensate the high mobility of Pt at the aging temperature above 900°C. The interaction between Pt and Rh needs to be redesigned to suit this kind of high temperature aging. Although the details are still not clear, an optimum degree of interaction exists for a new Pt/Rh catalyst. By combining the optimum Pt-Rh interaction concept and highly thermally durable materials, a new Pt/Rh catalyst, which performed equally under engine dynamometer and vehicle close-coupled test condition to the Pd/Rh, were developed. Surprisingly, this new Pt/Rh could reduce significant amount of Pt while maintaining the same performance level. The new Pt/Rh catalyst can be used at least for some applications where Pd/Rh catalysts are used. It is believed that the new Pt/Rh technology will help balance the PGM usage and facilitate the best utilization of PGM resource.