Study of the Promotion Effect of Iron on Supported Manganese Catalysts for NO Oxidation

Abstract

A series of TiO2 supported iron-manganese mixed oxide catalysts were studied for catalytic oxidation of NO to NO2. The oxidation activity was greatly enhanced with the addition of iron, by about 34% at 300°C. Mn(subscript 0.1)Fe(subscript 0.15)/Ti with the molar ratio of Mn:Fe = 1:1.5 showed the best oxidation activity. It was also found that the addition of iron oxide increased the resistance to H2O and SO2. The formation of byproduct N2O could generally be disregarded. A combination of various physico-chemical techniques was used to characterize the physical and chemical properties of these catalysts. The surface area did not change very much with the addition of iron. The XRD (X-ray diffraction) and HR-TEM (high-resolution transmission electron microscopy) results suggested that there was an interaction between manganese and iron, leading to the formation of manganese-iron composite oxides, which were in the amorphous phase. The XPS (X-ray photoelectron spectroscopy) and H2-TPR (temperature-programmed reduction) investigations demonstrated that this composite oxide with an amorphous structure increased the surface active oxygen, facilitated oxygen mobility and enhanced the oxidation-reduction ability over the catalysts, all of which were crucial factors for the increase in NO oxidation activity. The FTIR (Fourier transform infrared spectroscopy) results showed that nitrates worked as intermediiates which could be easily decomposed to nitrogen oxides. The introduction of iron into manganese oxides increased the formation of intermediates and reduced the formation of sulfates on the surface of the catalysts.