Mechanism of selective catalytic oxidation of ammonia to nitrogen over Ag/Al2O3

The mechanism of selective catalytic oxidation (SCO) of NH3 over Ag/Al2O3 was studied by NH3 temperature-programed oxidation, O2-pulse adsorption, and in situ DRIFTS of NH3 adsorption and oxidation. The essence which affects the low temperature activity of Ag/Al2O3 has been elucidated through the mechanism study. Different Ag species on Ag/Al2O3 significantly influence O2 uptake by catalysts; while different oxygen species affect the activity of NH3 oxidation at low temperature. The activated –NH could react with the atomic oxygen (O) at low temperatures (<140 °C); however, the –NH could also interact with the O2 at temperatures above 140 °C. At low temperatures (<140 °C), NH3 oxidation follows the –NH mechanism. However, at temperatures above 140 °C, NH3 oxidation follows an in situ selective catalytic reduction (iSCR) mechanism (two-step formation of N2 via the reduction of an in situ-produced NOx species by a NHx species).