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For global environmental protection and resource conservation, Honda has developed a low precious-metal perovskite catalyst system in response to LEV-II, which achieves both low emissions and a reduction in the amount of precious metal used. The amount of precious metals used in the catalyst, per vehicle, is expected to be 50% less than in conventional systems. This system is comprised of an air-fuel ratio control system based on Honda's unique high-accuracy air-fuel control system, combined with a perovskite catalyst jointly developed with the US Company CSI. This system's performance is expected to reach the levels required by LEV-II regulations. Perovskite is a mix-metal oxide material that is widely used in general applications other than catalysts. However, it has not been widely used in automobile catalysts, because, in comparison with precious-metal catalysts, both the heat resistance and conversion efficiency during the warm-up process is reduced.

The reduction of NOx in exhaust gas has been a major challenge in diesel engine development. For the NOx reduction issues, a new Lean NOx Catalyst (LNC) aftertreatment system has been developed by Honda. A feature of the LNC system is the method that is used to reduce NOx through an NH₃-Selective Catalytic Reduction (NH₃-SCR). In an LNC system NOx is adsorbed at lean conditions, then converted to NH₃ at rich conditions and subsequently reduced in the next lean phase. In recent years, as the efficiency of the diesel engine has improved, the exhaust gas temperatures have been reduced gradually. Therefore, the aftertreatment system needs to be able to purify NOx at lower temperatures. The development of a new LNC which has a high activity at low temperature has been carried out. For the improvement of the LNC three material improvements were developed. The first of these was the development of a NOx adsorbent which is matching the targeted exhaust gas temperatures.

Regulations that limit emissions of pollutants from gasoline-powered cars and trucks continue to tighten. More than 75% of emissions through an FTP-75 regulatory test are released in the first few seconds after cold-start. A factor that controls the time to catalytic light-off is the heat capacity of the catalytic converter substrate. Historically, substrates with thinner walls and lower heat capacity have been developed to improve cold-start performance. Another approach is to increase porosity of the substrate. A new material and process technology has been developed to significantly raise the porosity of thin wall substrates (2-3 mil) from 27-35% to 55% while maintaining strength. The heat capacity of the material is 30-38% lower than existing substrates. The reduction in substrate heat capacity enables faster thermal response and lower tailpipe emissions. The reliance on costly precious metals in the washcoat is demonstrated to be lessened.