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lSCR = Selective Catalytic Reduction
lAftertreatment to reduce NOx (NO & NO2) from combustion exhaust
lUrea (NH3) is injected into exhaust as reducing agent. 
lNH3 reacts with NOx on catalyst surface to form nitrogen and water
SCR Process Basics
4NO + 4NH3 + O2         4N2 + 6H2O
2NO2 + 4NH3 + O2         3N2 + 6H2O
Catalyst
Catalyst