Zaɓin yana nufin a cikin aikin mai haɓaka da yanayin kasancewar oxygen, NH3 ya fi girma da NOx don samar da nitrogen da ruwa, ba tare da oxygen a cikin hayaki ba, babban amsa shine:

4NO + 4NH3 + O2 →4 N2+6H2O(1)

2NO2 + 4NH3 + O2 → 3 N2+6H2O(2)

A cikin yanayin da babu catalyst, da aka ambata sinadarai halayen kawai a cikin wani m zafin jiki kewayon (980 ℃ a kusa da), da amfani da catalyst da amsa zafin jiki za a iya sarrafa a 300-400 ℃, daidai da hayaki gas zafin jiki tsakanin boiler mai ceton kwal da iska preheater, da aka ambata halayen ne dumama halayen, saboda NOx a hayaki gas karami,

Saboda haka, za a iya watsi da haɓaka zafin jiki na catalyst.