Denox systems typically use two primary methods: Selective Catalytic Reduction (SCR) and Non-Selective Catalytic Reduction (NSCR).
Selective Catalytic Reduction (SCR) In SCR, a reductant such as ammonia (NH₃) or a urea solution is injected into the exhaust stream. The mixture then passes over a catalyst, usually composed of materials like vanadium, tungsten, or zeolites. The catalyst facilitates the reaction between NOx and the reductant, converting NOx into nitrogen (N₂) and water (H₂O).
Non-Selective Catalytic Reduction (NSCR) NSCR is commonly used in rich-burn engines, where an excess of fuel is present. In this method, a three-way catalyst is employed to simultaneously reduce NOx, oxidize carbon monoxide (CO), and unburned hydrocarbons (HC). The catalyst typically contains platinum, palladium, and rhodium.
