Insights into the simultaneously enhanced activity, selectivity, and H2O resistance of cobalt modified MnCeOx/TiO2 catalyst for selective catalytic reduction of NOx with NH3

Abstract

The promotional effect of cobalt (Co) modification on MnCeOx/TiO2 catalyst for selective catalytic reduction of NO with NH3 (NH3-SCR) was investigated extensively in this study. A series of CoMnCeOx/TiO2 catalysts with different Co contents were prepared by the facile impregnation method and characterized by XRD, N2 sorption, XPS, H2-TPR, NH3/NO-TPD, and in situ DRIFT spectroscopy. The results indicate that the modification of MnCeOx/TiO2 by Co could significantly improve its low-temperature activity and N2 selectivity, and broaden operation temperature window (>95% NO conversion at 100–225 °C), and that the optimal mole ratio of Co to Ti in the catalyst is 0.4. Furthermore, the introduction of Co to MnCeOx/TiO2 could obviously enhance H2O resistance. The characterization results reveal that the addition of Co to the MnCeOx/TiO2 catalyst could enhance the dispersion of MnOx and CeOx, and increase the relative ratio of Mn4+ and Ce3+ on the catalyst surface. In addition, the surface area of MnCeOx/TiO2 is enlarged evidently after doping of Co. From the results of H2-TPR, NH3/NO-TPD, and NO oxidation, CoMnCeOx/TiO2 exhibits stronger reducibility, larger adsorption capacity for NH3 and NO, and higher NO to NO2 conversion than MnCeOx/TiO2, thus obtaining the higher SCR activity, N2 selectivity, and H2O tolerance. In situ DRIFT spectroscopy tests indicate that the NH3-SCR reaction on both MnCeOx/TiO2 and CoMnCeOx/TiO2 follow simultaneously the Langmuir-Hinshelwood and Eley-Rideal mechanisms.