Selective catalytic reduction of NO with NH 3 over manganese substituted iron titanate catalyst: Reaction mechanism and H 2O/SO 2 inhibition mechanism study

Abstract

Selective catalytic reduction (SCR) of NO with NH 3 over Mn substituted iron titanate catalyst (Fe 0.75Mn 0.25TiO x ) was fully investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy. At relatively low temperatures, both ionic NH 4 + and coordinated NH 3 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 NH 4NO 3 species was formed as intermediate species and its reactivity was also proved. An NH 3-SCR mechanism over Fe 0.75Mn 0.25TiO x at low temperatures was proposed accordingly, in which the reduction of NH 4NO 3 by NO was possibly the rate-determining step. Due to the mild and reversible inhibition effect of H 2O on NH 3/NO x adsorption, the SCR activity decline in the presence of H 2O was also slight and recoverable; however, the inhibition effect of SO 2 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.