Enhancement of Fe-Nb interaction by acid modification over SO42--FeOx-Nb2O5 catalyst for NH3 selective catalytic reduction of NOx

A series of iron-based composite oxide catalysts, modified with acid and niobium, were produced for the purpose of selective catalytic reduction of NOx with NH3 (NH3-SCR) via co-precipitation. The obtained SO42--FeOx-Nb2O5 (S-FeNbOx) catalyst exhibited significantly better SCR performance than the unmodified FeOx catalyst, with a NOx conversion above 90% and N2 selectivity higher than 95% in the temperature range of 275-450 degrees C. The characterization results suggest that the addition of Nb not only modifies the electronic structure and alleviates the reducibility but also enhances the surface acidity of the catalysts. The sulfuric acid modification of FeOxNb2O5 catalyst promotes the formation of redox-acid sites. The in situ Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) results revealed that the combining sulfuric acid and niobium modifications resulted in a significant increase in the amount of Bronsted acid sites, and also led to a blue shift of the band related to the Lewis acid sites, implying the existence of a synergistic effect of the two modification methods. The creation of redox-acid sites significantly enhances the adsorption and activation capacity of NH3 on the catalyst surface. These results suggest that the NH3-SCR reaction to primarily follow the Eley-Rideal (E-R) mechanism on the catalyst.