Development of Three-Way Catalysts Enhanced NOx Purifying Activity

Paper #:
  • 2018-01-0942

  • 2018-04-03
Increasing awareness of environmental protection requires more improvement of catalyst' performance. In order to purify emission out of engine(HC, CO, NOx) in high performance, precious metals are necessary as activate sites.However it is required to reduce precious metals used from viewpoint of protection of resources depletion because the number of vehicles ownedis globally increasing. In this paper, a high performance three-way catalyst has been developed with the application of a new washcoat structure to improve gas diffusivity along with a new pyrochlore-ceria/zirconia (CZ) that improves low temperature OSC performance to achieve the reduction of precious metal usage. In recent years the emission in the high load driving area represented by such as US06, WLTP, RDE is focused in the world. In this high load area, air fuel ratio is fluctuated remarkably with slight lean and rich condition. And in that situation NOx emission is increased because it is difficult to purify NOx at slight lean condition. Oxygen storage capacity (OSC) is important to purify the NOx emission. However, electronic state of Rh becomes oxide that cause decline of purifying activity when amount of OSC material is increased in washcoat. Therefore, we developed the catalyst including two technologies to secure high OSC performance with less declination of NOx purifying activity. At first, we developed new OSC material that has low-SSA and high OSC performance. Basically low SSA contributes to less declination of NOx purification. On the other hand it shows low OSC performance. Therefore we focused on pyrochlore-ceria/zirconia (CZ) and improved this material about OSC at low temperature. Secondly, we developed new technology of washcoat structure that has high gas diffusivity by making connected pore in washcoat. The connected pore means that some pores are connected each other unlike conventional structure have isolated pores. As a result the catalyst we have developed shows high NOx purifying activity with nearly 30% reduction of precious metal usage. (314 word)
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