Selective catalytic reduction (SCR) imagwiritsidwa ntchito kuwongolera NOx mu utsi wa injini ya dizilo.NH3 kapena urea (nthawi zambiri njira yamadzi ya urea yokhala ndi chiŵerengero cha 32.5%) imagwiritsidwa ntchito ngati kuchepetsa.Pansi pa zomwe O2 ndende ndi yoposa maulamuliro awiri apamwamba kuposa NOx ndende, pansi pa kutentha kwina ndi chothandizira, NH3 imagwiritsidwa ntchito kuchepetsa NOx ku N2 ndi H2O.Chifukwa NH3 imachepetsa NOx popanda kuchitapo kanthu ndi O2 poyamba, imatchedwa "selective catalytic reduction".