Abstract

Er-modified FeMn/TiO2 catalysts were prepared through the wet impregnation method, and their NH3-SCR activities were tested. The results showed that Er modification could obviously promote SO2 resistance of FeMn/TiO2 catalysts at a low temperature. The promoting effect and mechanism were explored in detail using various techniques, such as BET, XRD, H2-TPR, XPS, TG, and in-situ DRIFTS. The characterization results indicated that Er modification on FeMn/TiO2 catalysts could increase the Mn4+ concentration and surface chemisorbed labile oxygen ratio, which was favorable for NO oxidation to NO2, further accelerating low-temperature SCR activity through the “fast SCR” reaction. As fast SCR reaction could accelerate the consumption of adsorbed NH3 species, it would benefit to restrain the competitive adsorption of SO2 and limit the reaction between adsorbed SO2 and NH3 species. XPS results indicated that ammonium sulfates and Mn sulfates formed were found on Er-modified FeMn/TiO2 catalyst surface seemed much less than those on FeMn/TiO2 catalyst surface, suggested that Er modification was helpful for reducing the generation or deposition of sulfate salts on the catalyst surface. According to in-situ DRIFTS the results of, the presence of SO2 in feeding gas imposed a stronger impact on the NO adsorption than NH3 adsorption on Lewis acid sites of Er-modified FeMn/TiO2 catalysts, gradually making NH3-SCR reaction to proceed in E–R mechanism rather than L–H mechanism.

Highlights

  • Nitrogen oxides (NOx) emitted from diesel engines and industrial processes are significant atmospheric pollutants, which can lead to a number of environmental problems, such as acid rain, photochemical smog, ozone depletion, and greenhouse effects [1,2,3,4]

  • Tithhethdeiffsrtaacntdioanrdpepaokws der of MdnifOfrxacitniotnhepapttreerpnaorefdMFne2MO3n,/iTmiOp2lycinatgalMysnt2Om3atwchasedthwe mellaiwn ictrhystthael psthaansde.arTdhepdoiwffdraecrtion peaks of Mn2O3 in Er-modified FeMn/TiO2 catalysts were not obvious. This suggests that Er modification promoted the transformation of MnOx from crystalline state to highly dispersed amorphous state, which was beneficial to enhance the catalytic performance at low temperature [39,40]

  • After the SO2 resistance test, there were more peaks appeared in the diffraction pattern of the used FeMn/TiO2 catalyst, which could be ascribed to the formation of Ti(SO4)2 on catalyst surface (ICCD PDF-2, 18-1406) [41]

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Summary

Introduction

Nitrogen oxides (NOx) emitted from diesel engines and industrial processes are significant atmospheric pollutants, which can lead to a number of environmental problems, such as acid rain, photochemical smog, ozone depletion, and greenhouse effects [1,2,3,4]. A number of NOx removal technologies have been developed with the purpose of abating NOx emissions. Selective catalytic reduction (SCR) with NH3 (or urea) as a reductant is an effective and economic NOx removal technique. It has been widely used in stationary and mobile sources [5,6,7]. It is of great significance to develop vanadiumfree SCR catalysts with excellent catalytic activities at low temperatures (

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