Case 621G - Page 233

7-MAINTENANCE
SelectiveCatalyticReduction(SCR)catalyst
ThemainreactioninvolvedintheSCRcatalystisthecon-
versionoftheNO
x
toN
2
andwater(H
2
O).Anaverage
NO
2
/NO
x
ratioaround50%isrequiredtogivetheopti-
mumNO
x
reductionefciencyintheexhaustsystem.
Excessofammonia(NH
3
)isoftenusedtofacilitatethe
NO
x
reductiontonitrogen(N
2
),resultinginNH
3
slip.This
ammoniamustberemovedbyasecondarystepinthe
CleanUpCatalyst(CUC).
LEIL14WHL0450AA4
621G
LEIL13WHL0252AB5
721G
7-25