Which after-treatment system is used to reduce NOx emissions in diesel vehicles?

• A. Catalytic converter
• B. NOx adsorber
• C. Diesel particulate filter
• D. Diesel Oxidation Catalyst (DOC or OC)

Answer: (B)

NOx control in diesel engines relies on after-treatment systems that trap and periodically reduce NOx under lean exhaust. The NOx adsorber, also called a lean-NOx trap, captures NOx when the exhaust is lean by storing it as nitrates on the catalyst. During regeneration, the system shifts to a rich condition, which reduces the stored NOx to nitrogen and oxygen over the catalyst, releasing harmless gases. This mechanism specifically targets NOx emissions from lean-burn diesels, distinguishing it from devices that primarily oxidize hydrocarbons and carbon monoxide or filter particulates. A diesel particulate filter removes soot, the diesel oxidation catalyst oxidizes hydrocarbons and some CO, and a general catalytic converter handles various pollutants but not primarily NOx. Therefore, the NOx adsorber is the system used to reduce NOx emissions in diesel vehicles.