Innovative Materials with High Stability, High OSC, and Low Light-Off for Low PGM Technology

E. Rohart; O. Larcher; C. Hédouin; M. Allain; P. Macaudière; S. Deutsch

doi:10.4271/2004-01-1274

2004-03-08

Innovative Materials with High Stability, High OSC, and Low Light-Off for Low PGM Technology 2004-01-1274

To meet severe legislation limits, car manufacturers use close-coupled three-way catalysts (TWC) to reduce cold start emissions. These catalysts show long term durability and thermal stability at temperatures higher than 1000 °C. Mixed ceria-zirconia oxides are an important component of these TWCs. Ceria-rich, mixed oxides have a high crystalline structure defects density, and thus show high oxygen storage capacity (OSC). They are appropriate precious metal supports up to 1000°C. For applications which require higher thermal durability, zirconia-rich mixed oxides are used to make active catalysts because of their good thermal stability.

Rhodia has developed a new generation of mixed oxides with high OSC and high thermal stability, covering a wide range of compositions. These materials show phase stability and thermal stability at temperatures greater than 1100°C for Zr-rich as well as Ce-rich compositions. They can be used advantageously as precious metal carriers in close-coupled or underfloor catalysts demonstrating improved catalytic performance.

Regardless of composition (ceria-rich as well zirconia-rich mixed oxides), these materials show surface areas higher than 20 m²/g and 5 to 7 m²/g respectively after air aging at 1100°C and 1200°C.

Aged Rh model powder catalysts based on these new materials show improved hydrocarbon and CO light-off temperature compared to existing materials. Typically, the T20%-CO light-off temperature is 30°C less for a Ce-Zr (50/50 at%) based catalyst than for a zirconia-rich based catalyst. Pt based powder catalysts show the same trend. In addition, with new ceria-rich mixed oxide based catalysts, the cross-over point (COP) conversion is less affected by a decrease of the precious metal loading than with a catalyst based on a zirconia-rich mixed oxide.

Due to their high OSC, thermal stability and low light off performance, such materials are preferred precious metal carriers for cost effective catalysts with low precious metal loadings.

SAE MOBILUS

Subscribers can view annotate, and download all of SAE's content. Learn More »

Access SAE MOBILUS »

Digital $37.00 Print $37.00

Preview Document

We also recommend:

Standards

SAE Mobilus®

Publications

News

Events

Professional Development

A World in Motion (PreK-12)

Participate with SAE

SAE Membership

Donate

Innovative Materials with High Stability, High OSC, and Low Light-Off for Low PGM Technology 2004-01-1274

SAE MOBILUS