The reaction mechanism of the selective catalytic reduction (SCR) of NOx with NH3 over environmental-friendly iron titanate catalyst (FeTiOx) was investigated in detail. Over the iron titanate crystallite with specific Fe-O-Ti structure, both Bronsted and Lewis acid sites were present and involved in the SCR reaction. NH3 mainly adsorbed on titanium sites in the form of ionic NH4+ and coordinated NH3, while NOx mainly adsorbed on iron sites in the form of monodentate nitrate. In a relatively low temperature range (<200 degrees C), the SCR process mainly followed the Langmuir-Hinshelwood (L-H) mechanism, in which the formation of monodentate nitrate from NO oxidation by O-2 over Fe3+ was the rate-determining step. In contrast, in a relatively high temperature range (>200 degrees C), the SCR process mainly followed the Eley-Rideal (E-R) mechanism, in which the formation of NH2NO intermediate species following the H-abstraction of NH3 by neighboring Fe3+ was the rate-determining step. (C) 2011 Elsevier B.V. All rights reserved.