Abstract
A series of MnWOx/TiO2 catalysts were prepared by liquid phase deposition. The MnWOx/TiO2 catalyst was characterized by N2 physical adsorption, X-ray diffraction, H2 programmed temperature reduction, transmission electron microscopy and X-ray electron spectroscopy, and their NH3-SCR performance were tested. The effect of Mn valence on the NH3-SCR performance of MnWOx/TiO2 catalyst was analyzed and discussed. The results show that the active components are uniformly dispersed on the surface, and the average valence of manganese are different. The average valence state of manganese in Mn3WOx/TiO2 catalyst is the highest and the activity at low temperature is the best. On the contrary, the average valence of manganese in MnWOx/TiO2 catalyst is the lowest while the N2 selectivity is the best, which means that high valence of manganese is beneficial to its low temperature activity while low valence is favorable for its N2 selectivity.
Highlights
Nitrogen oxides (NOx) are one type of the major pollutants that affect air quality and can cause many environmental problems such as acid rain, smog, and photochemical pollution
The MnWOx/TiO2 catalyst was tableted, broken, and sieved to give 20-60 mesh solid particles. 0.5g catalyst was placed in a tube furnace, and the NOx concentration before and after NH3-selective catalytic reduction (SCR) reaction was measured by a TH200 nitrogen oxide analyzer and a Thermo 1500 chromatography
The Mn2p3/2 of the MnWOx/TiO2 catalyst can be divided into three sub-peaks by peak deconvolution: 642.0642.6eV can be attributed to Mn4+, 640.6-641.4eV can be attributed to Mn3+, and Mn2+ is at 643.4644.5eV [16,17]. combining Fig. 3 and Table 2, the valence of Mn species in the Mn3WOx/TiO2 catalyst is mainly Mn4+, while in the Mn2WOx/TiO2 catalyst and the MnWOx/TiO2 catalyst, the Mn species are mainly at Mn3+ and Mn2+, respectively. This proves that the valence state of manganese in the catalyst can be adjusted by changing the Mn/W ratio of the catalyst, and the average valence state of manganese decreases with the tungsten content increasing
Summary
Nitrogen oxides (NOx) are one type of the major pollutants that affect air quality and can cause many environmental problems such as acid rain, smog, and photochemical pollution. One of the disadvantages of the V2O5-WO3(MoO3)/TiO2 catalyst is that the operating temperature window is mainly in the range of 300-400 oC, which means that it cannot effectively remove the nitrogen oxides in the low temperature environment and raise the energy consumption. Researchers are working hard to develop new catalysts that have high NH3-SCR activity at lower temperatures. Among these potential catalyst systems, manganese oxide exhibits the best deNOx activity in the low temperature range due to its variable valence and good redox performance [9]. The influence of valence state of manganese on the NH3-SCR was discussed
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