NOx Catalyst

📖 YOUCANIC Automotive Glossary

The NOx catalyst (also called a lean NOx trap, NOx storage catalyst, or NOx adsorber) is an exhaust aftertreatment device used on some diesel and lean-burn gasoline engines to reduce nitrogen oxide emissions through a chemical trapping and regeneration process. During normal lean operation, the catalyst adsorbs (traps) NOx molecules onto a barium or potassium coating on the substrate. When the trap reaches capacity, the ECU briefly commands a rich exhaust condition which causes the stored NOx to be released and converted into harmless nitrogen gas. This trap-and-release cycle repeats continuously during driving.

NOx catalysts are used as an alternative to or in conjunction with SCR/DEF systems on some diesel vehicles. Failures cause high NOx emissions, P-codes related to catalyst efficiency, and potential derate conditions on diesel vehicles. NOx catalyst degradation is accelerated by sulfur in fuel and oil — low-sulfur diesel and low-SAPS (Sulfated Ash, Phosphorus, Sulfur) engine oil are critical for longevity. Some vehicles require periodic desulfation cycles where the ECU raises exhaust temperatures to burn off accumulated sulfur compounds from the catalyst.