Selective catalytic reduction of NO with NH3 over manganese substituted iron titanate catalyst: Reaction mechanism and H2O/SO2 inhibition mechanism study

Selective catalytic reduction (SCR) of NO with NH3 over Mn substituted iron titanate catalyst (Fe0.75Mn0.25TiOx) was fully investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy. At relatively low temperatures, both ionic NH4+ and coordinated NH3 contributed to the SCR reaction, and both bridging nitrate and monodentate nitrate were confirmed to be the reactive nitrate species. In the SCR reaction condition, surface NH4NO3 species was formed as intermediate species and its reactivity was also proved. An NH3-SCR mechanism over Fe0.75Mn0.25TiOx at low temperatures was proposed accordingly, in which the reduction of NH4NO3 by NO was possibly the rate-determining step. Due to the mild and reversible inhibition effect of H2O on NH3/NOx adsorption, the SCR activity decline in the presence of H2O was also slight and recoverable; however, the inhibition effect of SO2 was much more intense and irreversible, because the formation of nitrate species was totally inhibited by the formation of sulfate, resulting in the cut-off of the SCR reaction pathway at low temperatures.