Selective catalytic reduction (SCR) systems work by chemically reducing NOx (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.

The SCRF® system integrates Selective Catalytic Reduction (SCR) with a soot filter – the next step for diesel NOx.

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 NOx reduction).


SCRF® system

SCRF® system

Johnson Matthey's Three Way Filter (TWF®) technology can reduce particle number by 50 ‐ 90% on gasoline direct injection engines.

Ammonia-SCR

Ammonia-SCR

Ammonia-SCR systems react ammonia (NH 3) with the NOx to form nitrogen (N2) and water (H2O).

Hydrogen-SCR

Hydrogen-SCR

Hydrocarbon-SCR (lean NOx reduction) systems use hydrocarbons as the reductant.