Fe-Mn/Al2O3 catalysts for low temperature selective catalytic reduction of NO with NH3

Abstract

A series of Fe-Mn/Al2O3 catalysts were prepared and studied for low temperature selective catalytic reduction (SCR) of NO with NH3 in a fixed-bed reactor. The effects of Fe and Mn on NO conversion and the deactivation of the catalysts were studied. N2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, H2 temperature-programmed reduction, NH3 temperature-programmed desorption, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis and Fourier transform infrared spectroscopy were used to characterize the catalysts. The 8Fe-8Mn/Al2O3 catalyst gave 99% of NO conversion at 150 °C and more than 92.6% NO conversion was obtained in a wide low temperature range of 90–210 °C. XPS analysis demonstrated that the Fe3+ was the main iron valence state on the catalyst surface and the addition of Mn increased the accumulation of Fe on the surface. The higher specific surface area, enhanced dispersion of amorphous Fe and Mn, improved reduction properties and surface acidity, lower binding energy, higher Mn4+/Mn3+ ratio and more adsorbed oxygen species resulted in higher NO conversion for the 8Fe-8Mn/Al2O3 catalyst. In addition, the SCR activity of the 8Fe-8Mn/Al2O3 catalyst was only slightly decreased in the presence of H2O and SO2, which indicated that the catalyst had better tolerance to H2O and SO2. The reaction temperature was crucial for the SO2 resistance of catalyst and the decrease of catalytic activity caused by SO2 was mainly due to the sulfate salts formed on the catalyst.