Influence of different supports on the physicochemical properties and denitration performance of the supported Mn-based catalysts for NH3-SCR at low temperature

Abstract

The commonly used supports of SiO2, γ-Al2O3, TiO2, and CeO2 were synthesized, and used for preparing MnOx/SiO2, MnOx/γ-Al2O3, MnOx/TiO2, and MnOx/CeO2 catalysts with the purpose of investigating the influence of crystal structure and coordination status on the physicochemical properties and denitration performance of these supported Mn-based catalysts for low-temperature NH3-SCR. The obtained samples were characterized by XRD, Raman, BET, H2-TPR, NH3-TPD, in situ DRIFTS, NO+O2-TPD, XPS, and NH3-SCR model reaction. XRD results indicate that MnOx species can be highly dispersed on the surface of γ-Al2O3, TiO2, and CeO2, which is because that there are some octahedral and tetrahedral vacancy sites, octahedral vacancy site, and cubic vacancy site exist on the surface of defective spinel structure γ-Al2O3, anatase TiO2, and cubic fluorite-type structure CeO2, respectively. However, there is no any vacancy site on the surface of SiO2 due to its unique SiO4 tetrahedral structure, which results in the appearance of crystalline β-MnO2 on the surface of MnOx/SiO2 catalyst. Furthermore, H2-TPR results exhibit obvious different reduction behavior among these supported Mn-based catalysts, which is explained by the coordination status of Mn species. Finally, NH3-SCR model reaction results show that MnOx/γ-Al2O3 catalyst presents the best catalytic performance among these supported Mn-based catalysts due to its high dispersion, suitable reduction behavior, largest amount of acid sites, optimal NOx adsorption capacity, and abundant Mn4+ content.