NH3-SCR Performance of Mn-Fe/TiO2 Catalysts at Low Temperature in the Absence and Presence of Water Vapor
2016
Zhu, Lin | Zhong, Zhaoping | Yang, Han | Wang, Chunhua
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.
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