Development of Low Temperature Active Three Way Catalyst 2019-01-1293

In recent years, fuel efficiency has been improved by using many technologies such as downsizing engine, turbocharger and direct injection to reduce CO₂ emissions from vehicle. However, the temperature of the exhaust gas from the engines using these technologies becomes lower than that form conventional one. That increases the difficulty for three-way catalyst (TWC) to purify CO, HC and NOx enough because TWC is not warmed up just after engine starting. In order to reduce cold emission mentioned above, we have been studying the warmup strategy of which the key property is thermal mass of TWC. To achieve early warmup, thermal mass of TWC is reduced by lightening the weight of (1) substrate and (2) catalytic materials, namely washcoat amount. Along with the strategy, we have developed TWC with lightweight substrate and applied it from the 2016 model year CIVIC. It is predicted that the reduction of washcoat amount results in enhancing temperature rising performance because of the decrease in thermal mass but deteriorating exhaust gas purification performance after aging due to the degradation of reactivity, thermal durability and phosphorus poisoning resistance. In this research, the effects of washcoat amount on both of temperature rising and purification performance of TWC were investigated. To realize the TWC with super low thermal mass, washcoat materials such as alumina, and material with oxygen storage capacity (OSC) were newly developed. The temperature rising and exhaust gas purification performance of the low thermal mass TWC applying new materials were evaluated by vehicle test. As a result, approximately 25% of exhaust gas was reduced by using our newly developed TWC compared to conventional one even after aging, confirming that the developed TWC conforms to the US LEVIII SULEV30 emission standard.