Development of Advanced Pd/Rh Automotive Catalyst

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. It is still generally true that Pd-based catalyst is suitable for close-coupled application.

In this paper, an advanced Pd/Rh is reported to be improved for both cold start and hot emissions. Pd based catalyst has been an excellent catalyst for removing THC and CO at light-off but is weak in NOx. In order to elevate the NOx activity of Pd-based catalyst, Rh has been combined into the catalyst system. The Pd-Rh, Pd-OSC and Rh-OSC interactions were found to be important for the improvement of light-off and warmed-up activities on Pd/Rh catalyst. Minimizing Pd-Rh interaction was effective for Pd/Rh catalyst performances. Selections of supporting materials for both Pd and Rh are a key for improvement of light-off and warmed-up activities. By combining the above concepts, the advanced Pd/Rh, which was significantly superior to the current Pd/Rh under engine dynamometer and vehicle close-coupled test condition, was developed.