What is Selective Catalytic Reduction (SCR) and how does it work?

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Selective Catalytic Reduction (SCR) is an after treatment technology that uses a urea based diesel exhaust fluid (DEF) and a catalytic converter to significantly reduce oxides of nitrogen (NOx) emissions. The purpose of the SCR system is to reduce levels of NOx (oxides of nitrogen emitted from engines) that harm our health and the environment. Small quantities of diesel exhaust fluid (DEF) are injected into the exhaust upstream of a catalyst, where it vaporizes and decomposes to form ammonia and carbon dioxide. The ammonia (NH3) is the desired product, which in conjunction to the SCR catalyst, converts the NOx to harmless nitrogen (N2) and water (H2O).