The CeO 2 -TiO 2 (CeTi) and CeO 2 /WO 3 -TiO 2 (CeWTi) catalysts were prepared by a sol-gel precipitation method and their NH 3 -NO/NO 2 selective catalytic reduction (SCR) performance was studied. N 2 O formation and effect of oxygen concentration on SCR performance over CeWTi catalyst were also investigated while varying the NO 2 /NO x ratio. Results indicate that fast SCR behavior of CeWTi catalyst has the best NH 3 -NO/NO 2 SCR performance due to the catalyst reoxidation rate by NO 2 higher than by O 2 . Compared with CeTi catalyst, CeWTi catalyst exhibits higher de-NO x performance under NH 3 -NO/NO 2 SCR conditions. As the CeTi and CeWTi catalysts exhibit similar redox property, addition of WO 3 provides more acid sites which accelerate the reaction between NH 4 NO 3 and NO to get a superior low-temperature activity. Amount of N 2 O formation shows a peak at 250 °C mainly derived from NH 4 NO 3 decomposition.
Lei Chen,Zhichun Si,Xiaodong Wu,Duan Weng,Zhenwei Wu
A MnO x –NbO x –CeO 2 catalyst for low temperature selective catalytic reduction (SCR) of NO x with NH 3 was prepared by a sol–gel method, and characterized by NH 3 –NO/NO 2 SCR catalytic activity , NO/NH 3 oxidation activity, NO x /NH 3 TPD , XRD , BET, H 2 -TPR and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The results indicate that the MnO x –NbO x –CeO 2 catalyst shows excellent low temperature NH 3 -SCR activity in the temperature range of 150–300°C. Water vapor inhibits the low temperature activity of the catalyst in standard SCR due to the inhibition of NO x adsorption. As the NO 2 content increases in the feed, water vapor does not affect the activity in NO 2 SCR. Meanwhile, water vapor significantly enhances the N 2 selectivity of the fresh and the aged catalysts due to its inhibition of the decomposition of NH 4 NO 3 into N 2 O.
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