Selective Catalytic Reduction (SCR Catalyst)

Selective catalytic reduction (SCR) systems work by chemically reducing NO_x (NO and NO₂) to nitrogen (N₂). In a lean gas stream, it is necessary to add a reductant to the system to enable this reaction. There are two main classes of SCR system, defined by the source of the reductant used. These are ammonia-SCR (of which urea-SCR is the most common) and hydrocarbon-SCR (lean NO_x reduction).