High Thermostable Hybrid Zirconia Materials for Low Loading Precious Metal Catalyst Technology 2005-01-1107
To meet severe legislation limits and reduce cold start emissions, car manufacturers use improved engine control technologies, supports with higher cell densities, lower thermal mass, turbulent like flows, and bring the three-way catalysts (TWC) closer and closer to the engine. These catalysts show long term durability and thermal stability at temperatures higher than 1000 °C. Thus PGM carriers are extensively investigated to assure high activity and long term durability with low PGM loading.
Hence Rhodia has developed a new generation of hybrid Zirconia oxides. These materials show phase stability and thermal stability at temperatures higher than 1100°C, and keep PGM available after harsh aging, as even at very low PGM loadings.
In this paper we focus first, on stability and catalytic performance of laboratory aged PGM powder model catalysts. We show that there is a strong relationship between catalytic activity and the nature of the PGM/support interaction. For example high thermostable rare-earths doped zirconia containing 40% Ceria, promotes the light-off activity of Rh model catalysts - T20% of NO and C3H6 are respectively lower by 40°C and 50°C under rich conditions and respectively lower by 30 and 20°C under lean conditions, than current OSC Zr-rich materials containing only 20% Ceria. On the other hand, high thermostable Ce-rich oxides (containing more than 50% Ceria) are preferred carriers for Pt. The same type of approach is issued to test the preferred PGM (Pt, Pd, Rh) / Support interaction.
In a second part we -combine the pre-screened mixed oxides in low loaded Pd/Rh and Pt/Rh technologies. These technologies are tested respectively on vehicle and synthetic gas bench (SGB). Low loading Pd/Rh technology containing only 22 g/ft3 PGM meets euro 4 limits and shows similar efficiency as current catalysts containing 35 g/ft3 PGM. The same trend is observed for Pt/Rh technologies on SGB test.