A series of iron−niobium composite oxides for selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) were prepared by coprecipitation with the assistance of CTAB. The obtained FeNb 0.4 O x -C catalyst exhibited superior SCR performance, with NO x conversion above 90% at 250−400 °C under a high GHSV of 250 000 h −1 . Characterization of the oxides by N 2physisorption, XRD, Raman, TG/DTA, NH 3 -TPD, H 2 -TPR, and XPS showed that when CTAB was present during preparation, a strong interaction between Fe and Nb was produced for the Fe− Nb catalysts made with an appropriate proportion of the two elements, which promoted the formation of γ-Fe 2 O 3 . The strong Fe−Nb interaction not only induced more reducible Fe at low temperatures but also enhanced the surface acidity, both of which brought about more active sites on the FeNb 0.4 O x -C catalyst. Owing to such strong interaction between redox-acid sites, more NO x species were adsorbed and activated over FeNb 0.4 O x -C, thus exhibiting high reactivity during the NH 3 -SCR reaction, which was revealed by DRIFT and kinetic studies.

Fe 2 O 3 -based catalysts have promising potential in the selective catalytic reduction (SCR) of NO with NH 3 with the advantages of environmental friendliness, excellent medium−high SCR activity, good N 2 selectivity, and high SO 2 tolerance. However, the NH 3 -SCR mechanism over Fe 2 O 3 -based catalysts remains highly uncertain and controversial due to the complex nature of the SCR reaction. Herein, the NH 3 -SCR reaction pathways over the α-Fe 2 O 3 (012) surface are elucidated at the atomic level by density functional theory calculations and experimental measurements. We demonstrate that, different from the NH 3 activation mechanism in numerous SCR catalytic systems, the reaction tends to follow the NO activation mechanism, in which NO activated at Fe sites reacts with NH 3 to form a NH 2 NO intermediate and further decomposes into N 2 and H 2 O, in synchronization with the formation of a surface OH group. Subsequently, the catalyst is regenerated by an O 2 -assisted surfacedehydrogenation process. The activation of NO as well as the formation of the NH 2 NO intermediate is the rate-determining step of the complete SCR cycle. This study enhances the atomic-level understanding toward the NH 3 -SCR reaction and provides insights for the development of Fe 2 O 3 -based SCR catalysts.