Tailored temperature window of MnOx-CeO2 SCR catalyst by addition of acidic metal oxides

A MnOx-CeO2 catalyst was modified with various acidic metal oxides (Nb205, W03, and Mo03) using a sal-gel method. The activities of the obtained catalysts were measured for the selective catalytic reduction (SCR) of NOx with NH3 to screen suitable acidic metal oxides for different temperature windows. The catalytic activities for NO and NH3 oxidation were also evaluated. The catalysts were characterized by X-ray diffraction, N-2 adsorption, H-2 temperature-programmed reduction, NH,/NO, temperature-programmed desorption analyses, and infrared spectroscopic measurements of NH3/NOx adsorption. The MnOx-CeO2 catalyst exhibited the greatest low-temperature (100-150 degrees C) activity. The addition of acidic metal oxides weakened the redox properties of the catalyst, resulting in inhibition of the partial oxidation of the adsorbed NH3 and NO2-assisted fast SCR reactions. Meanwhile, the oxidation of NH3 at relatively high temperatures (250-350 degrees C) was suppressed, and the adsorption of NH3 on Bronsted and Lewis acid sites was strengthened. Consequently, the temperature window of SCR reaction shifted to higher temperatures in the order Nb2O5< WO3< MoO3. (C) 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.