Catalyst technology for the gasoline engine cars
CO2, carbon dioxide, is regarded as one of the greenhouse effect gases which causes global warming. Emission from cars contains a large amount of CO2 so it is necessary to improve fuel efficiency in order to reduce CO2 emission. (Fig. 2: Calculation formula of CO2 emission in 1km driving) Therefore, fuel efficiency regulations aimed at reducing CO2 emission has been tightened since 2000 not only in U.S., Europe, and Japan but also in developing countries. (Fig. 1: CO2 regulations in Europe.)
Recent years, lean-burn engine that burns in excess oxygen atmosphere is reconsidered as one of the technologies to improve automobile fuel efficiency for the regulations in each country. This engine had been installed in many types of cars for the purpose of controlling fuel efficiency since early 90s. But it generated nitrogen oxide (NOx) like diesel engine did due to burning in excess oxygen. Therefore, the lean-burn engine hasn't been installed in almost entirely new cars which was sold after 2000s with tightening emission control.
Under the circumstances we regarded optimizing arrangement of "Substance with NOx storage function" and "PGM with catalytic function" as an essential technology and have succeeded in high dispersion arrangement of "NOx storage substance" in vicinity to PGM.
"By this development, we have achieved ""NOx storage"" and ""Making function of NOx storage and reduction more efficient"" then have satisfied both fuel efficiency improvement and NOx purification."
NSR (NOx storage-reduction) catalyst is based on the technology to efficiently purify or convert NOx (nitrogen oxide) contained in the lean-combustion emission gas into N2.
NOx emissions from the lean-burn gasoline-engine will be first occluded by the NOx storage materials through PGM and then purified into nitrogen gas (N2), by use of the reduction materials such as CO, H2 and HC that are provided from the engine during its rich-burning for a moment. This NSR catalyst is usually set for a fuel-efficient diesel-engine and a lean-burn gasoline engine.
In order to meet the needs of both the purification of vehicle emissions and the better fuel efficiency, the more improvement in NSK's performance is required.
"Nitrogen oxide (NO) contained in the gas emissions becomes oxidized on the surface of precious metal and temporarily gets occluded in the NOx storage materials, to be as ""NOx"". [See Fig. on the left side: NOx storage] If reduction materials (from over fuel-driving) are regularly added, NOx gets released from the NOx storage materials and reduction-purified on the surface of precious metal. [See Fig. on the left side: NOx storage-reduction ] ""NOx"" purification are implemented even on a lean-burn gasoline engine, due to the occlusion of the larger amount of ""NOx"" and its efficient reduction that repeats occluding at high speed. "
We have developed the unique technologies for optimizing the catalytic function by precious metal and NOx storage function by NOx storage materials. By this technology, we succeeded in making a highly dispersive placement of NOx storage materials nearby precious metal. This technology enabled the occluded NOx to be efficiently adsorbed onto the surface of precious metal as well as the catalyst's total storage-reduction reaction efficiency to improve.