NH3-SCR Performance of Mn-Fe/TiO2 Catalysts at Low Temperature in the Absence and Presence of Water Vapor

Abstract

Mn-Fe/TiO2 catalysts synthesized by sol-gel and co-precipitation methods were used for the selective catalytic reduction (SCR) of NO with NH3. The catalysts were characterized by N2 physisorption, XRD, NH3/NOx-TPD, and H2-TPR. The catalytic activities for SCR and NH3/NO oxidation were investigated in the absence and presence of water. In this study, Mn-Fe/TiO2(S) catalyst exhibited better catalytic activity at low temperature below 175 °C in the absence of H2O. However, more by-product of N2O was observed in this case in contrast with Mn-Fe/TiO2(C). The similar phenomenon was observed during the process of NH3 catalytic oxidation. The excellent redox capability and abundant active adsorbed species on the catalyst surface accounted for higher NOx conversion and more N2O formation for Mn-Fe/TiO2(S). It was found that water vapor hindered the activation of NH3 and adsorption-oxidation of NO, and thus, impeded catalytic activity of Mn-Fe/TiO2 during standard SCR process at low temperature, even though it reduced the formation of N2O. The inhibition for over dehydrogenation of amide adsorbed species and the deceleration for decomposition of ammonium nitrate species might be two reasons accounting for the decrease of N2O concentration in the presence of H2O. The different catalysts exhibited the different poisoning resistance to SO2 and the SO2 resistance of manganese-based catalyst at low temperature still needed the further improvement.