Selective Catalytic Reduction (SCR)
Selective Catalytic Reduction of NOx (SCR deNOx) is a technology applied on diesel engines to reduce the NOx emissions, by injecting a urea-water solution (AdBlue) into the exhaust gas upstream of the SCR catalyst, generating ammonia (NH3). This is absorbed onto the catalyst, converting NOx in diatomic nitrogen (N2) and water (H2O).
SCR and DPF are often combined because then all gaseous as well as particulate emissions are reduced (by 70% or more) and usually the most stringent (future) emission legislation can be met. SCR and DPF often work together nicely leading to an increased SCR efficiency. One of the technical options is the “SCR on DPF technology”, where the DPF part acts as an SCR catalyst as well. This can lead to a more compact configuration.