Effect of water vapor on NH3–NO/NO2 SCR performance of fresh and aged MnOx–NbOx–CeO2 catalysts

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.