Ordered mesoporous phosphotungstate nanostructure loading dispersed iron oxide as a promising NH3-SCR catalyst: Synergistic effect of redox sites and acid centers

Abstract

An ordered mesoporous phosphotungstate loading dispersed iron oxide is obtained as Fe/NPW catalyst for NH3-SCR. The Fe/NPW catalyst exhibits higher than 90 % NOx conversion at 250–475 °C and excellent SO2 tolerance since the ordered and uniform mesoporous structure favors the diffusion of reactants and dispersion of active ingredients. Moreover, the high dispersion enhances the interfacial interaction between Fe and W species on Fe/NPW catalyst, increasing the W5+/(W5++W6+) ratio to promote the formation of oxygen vacancies and surface adsorbed oxygen (Oα). Additionally, the synergistic effect of the redox sites and acid centers enabled by the dispersed iron oxide on the ordered mesoporous phosphotungstate provides moderate redox property and enhanced surface acidity. It improves the adsorption of NH3 and inhibits the over-oxidation of NH3 that occurs on Fe2O3 surface. Furthermore, the in-situ DRIFTS results show that the abundant surface acidity of phosphotungstate can suppress the formation of nitrate species. The introduction of Fe provides redox sites for reaction and enhances the thermal stability and activation of ammonia species adsorbed on Lewis acid sites, facilitating the Eley-Rideal pathway on Fe/NPW catalyst. The results of this work reveal that the synergistic effect of redox sites and acid centers on the ordered mesoporous Fe/NPW catalyst contributes to the excellent performance in the NH3-SCR process.