SCR, selective catalytic reduction, is a process that reduces harmful nitrogen oxide (NOx) emissions by turning them into harmless N2 and H2O molecules.
Ammonia (NH3) has proved to be the reducing agent with the best selectivity. It is not used in pure form but as an aqueous urea solution known as AdBlue. A dosing module injects a small amount of the reductant into the exhaust system, into the SCR catalytic converter.
After a period of use, the SCR catalyst also needs maintenance to keep working within factory limits.
