Restart NOx emission suppression material (SRR-MIX^*)

Reduction of exhaust gas in real driving emission (RDE^*)

The next round of European regulations, Post Euro 6 and Euro 7, will strengthen fuel consumption regulations to reduce carbon dioxide (CO₂) emissions as a response to the problem of global warming, while at the same time, nitrogen oxides (NOx) and PM (micron-sized solids such as soot, and liquid microparticulate matter), which are causes of air pollution, are also said to be regulated more strictly than ever before.

The atmosphere of exhaust gas from the engine _(*) changes depending on how the car is used in each region. For example, the atmosphere, temperature, and flow velocity of exhaust gas are different on roads with frequent acceleration and deceleration due to traffic jams and on highways such as autobahns. The next regulation will strongly require the reduction of exhaust emissions in such a real driving environment (RDE).

What is required for exhaust gas purification catalysts for automobiles

Differences in emissions between conventional vehicles and idling stop vehicles

• In a conventional vehicle, once the engine is started, the engine will continue to run even if the accelerator pedal is not depressed. This state is called idling, and gasoline is consumed little by little. On the other hand, idling stop vehicles, which have become popular in recent years, stop the engine for a certain period of time, such as at a red light, and restart the engine when the accelerator is depressed to resume driving. Idling stop vehicles may emit nitrogen oxides (NOx) when restarting.
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Engine control and NOx emission behavior of conventional and fuel-efficient vehicles

Why is NOx emitted when restarting an idling stop vehicle?

Nitrogen oxides (NOx) are emitted when restarting an idling stop vehicle because the atmosphere of the exhaust gas flowing into the catalyst changes due to differences in engine control. In the case of a conventional vehicle, the engine is kept running in an idling state (ready to start at any time) while waiting for a signal, so the gas atmosphere in the exhaust system is maintained, and the precious metal in the catalyst can be kept active. However, the idling stop vehicle has its engine stopped while waiting for a traffic light, so that excess oxygen in air flows into the catalyst, which makes the precious metals an inactive oxidized state. If the engine is restarted in this state, the exhaust gas from the engine cannot be purified and NOx emissions will occur.

Development that changes the properties of the carrier rather than suppressing deterioration of the precious metal it supports

The material (carrier) used in automotive catalysts consists of zirconium (Zr) oxides to which elements such as cerium oxide (CeO₂) and lanthanum oxide (La₂O₃) are added. Toxic gases are purified by supporting (adhering) precious metals to the carrier, but the properties of precious metals change depending on the composition of the carrier. Conventional catalyst development has focused on the concept of suppressing the deterioration of precious metals. For example, the purpose is to prevent the deterioration of precious metals by adding elements that improve heat resistance to Zr oxide, and stabilize the scaffold. At Cataler, instead of suppressing the deterioration of precious metals, we wondered whether it would be possible to improve the purification performance of the catalyst by changing the properties of the carrier that is the scaffold. We are now developing catalysts from this viewpoint.

Conventional catalyst development has focused on the concept of suppressing the deterioration of precious metals. For example, the purpose is to prevent the deterioration of precious metals by adding elements that improve heat resistance to Zr oxide, and stabilize the scaffold.
At Cataler, instead of suppressing the deterioration of precious metals, we wondered whether it would be possible to improve the purification performance of the catalyst by changing the properties of the carrier that is the scaffold. We are now developing catalysts from this viewpoint.