7
l
SCR =
S
elective
C
atalytic
R
eduction
l
Aftertreatment to reduce NO
x
(NO & NO
2
) from
combustion exhaust
l
Urea (NH
3
) is injected into exhaust as reducing agent.
l
NH
3
reacts with NO
x
on catalyst surface to form
nitrogen and water
SCR Process Basics
4NO + 4NH
3
+ O
2
4N
2
+ 6H
2
O
2NO
2
+ 4NH
3
+ O
2
3N
2
+ 6H
2
O
Catalyst
Catalyst