LeanNOxTrap

LeanNOxTrap, or LNT, is an automotive exhaust aftertreatment catalyst designed to reduce nitrogen oxides (NOx) emitted by lean-burn engines. It stores NOx during periods of excess oxygen and periodically regenerates the stored NOx during brief rich pulses, converting NOx to nitrogen, carbon dioxide, and water.

Mechanism and materials: The storage phase uses a NOx storage compound, typically barium-based, dispersed on high-surface-area supports such as alumina or ceria-zirconia, with noble metals like platinum and palladium to promote redox reactions. An oxygen storage component helps balance the redox state. NOx is stored as nitrate on Ba sites; during regeneration, reductants in the exhaust (unburned hydrocarbons, CO) reduce the nitrate to N2, CO2, and H2O.

Operation and challenges: LNT requires periodic regeneration cycles and is sensitive to catalyst temperature, sulfur compounds, and aging. Sulfates poison Ba-based storage, reducing NOx uptake; cold-start and low-temperature operation also limit performance. Regeneration consumes fuel and adds control complexity. LNT performance declines over time due to thermal aging and contaminant poisoning.

Applications and context: LNT has been used in diesel and lean-burn gasoline applications and is often integrated with other aftertreatment devices, such as diesel oxidation catalysts and selective catalytic reduction systems, to broaden NOx control across temperatures. Compared with SCR, LNT can operate without urea or hydrocarbon dosing but relies on regeneration control and has tighter constraints on sulfur and operating temperature.

History and status: Development began in the 1990s; while LNT technology has matured, many programs now favor SCR for diesel NOx control, with LNT deployed in specific niche applications or older platforms.