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NOx Adsorbers

8 August 2007

Nissan Motor announced that a new clean diesel technology using high-performance catalysts may be able to meet California super-ultra-low emission vehicle (SULEV) standards, which are equivalent to the EPA Tier 2 Bin 2 emission requirements. Nissan will further research the technology for commercial application in its future products.

Nissan clean diesel technology is based on three components: (1) modulated-kinetic (MK) combustion which simultaneously reduces NOx and PM emissions in the engine cylinder, (2) high-performance catalysts, and (3) advanced engine control system which controls oxygen level in the exhaust more precisely for better fuel efficiency and lower emissions.

The exhaust aftertreatment system includes a close-coupled diesel oxidation catalyst (DOC), followed by a “HC-NOx trap catalyst” and a diesel particulate filter (DPF).

The Nissan’s HC-NOx trap catalyst is an advanced NOx adsorber utilizing three catalyst layers: a hydrocarbon trap layer, a NOx adsorber layer, and a NOx reduction layer at the surface. During lean operation, hydrocarbons are stored in the HC trap layer, and NOx is stored in the NOx adsorber layer. During the rich regeneration phase, the stored HCs are transformed into H2+CO gas, which in turn is used to reduce the stored NOx to nitrogen.

Nissan had previously announced clean diesel technology that would meet the EPA Tier 2 Bin 5 standards (NOx = 0.07 g/mi; HC = 0.09 g/mi). With this new HC-NOx trap catalyst technology, Nissan believes it will be able to achieve EPA Tier 2 Bin 2 and California SULEV standards (NOx = 0.02 g/mi; HC = 0.01 g/mi).

In a separate announcement, Nissan said it plans to introduce a diesel version of its X-Trail SUV in the Japanese market in the fall 2008, two years ahead of the initial schedule. The vehicle will meet the JP 2009 emission standards (NOx = 0.08 g/km).

Source: Nissan | Asahi