Design of High-Performance Iron–Niobium Composite Oxide Catalysts for NH3-SCR: Insights into the Interaction between Fe and Nb

A series of iron–niobium composite oxides for selective catalytic reduction of NOx with NH3 (NH3-SCR) were prepared by coprecipitation with the assistance of CTAB. The obtained FeNb0.4Ox-C catalyst exhibited superior SCR performance, with NOx conversion above 90% at 250–400 °C under a high GHSV of 250 000 h–1. Characterization of the oxides by N2-physisorption, XRD, Raman, TG/DTA, NH3-TPD, H2-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-Fe2O3. 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 FeNb0.4Ox-C catalyst. Owing to such strong interaction between redox-acid sites, more NOx species were adsorbed and activated over FeNb0.4Ox-C, thus exhibiting high reactivity during the NH3-SCR reaction, which was revealed by DRIFT and kinetic studies.