| Recently,NOx has become one of the hot points of environmental issues because It's very harmful and more difficult to be removed. At present, the technology of the selective catalytic reduction is the most effective way to remove NO,, but the reaction temperature must be controlled by more than 380?. In order to save energy and reduce costs, the high efficiency of low-temperature SCR catalysts has become a research focus at home and abroad.In recent research, Mn-based catalysts have low reaction condition and the good potential for industrial application, but some drawbacks. In this paper, Mn-based catalysts were optimized,and the composite catalyst with high activities of low-temperature for the preparation of more stable, better activity and prevent poisoning of SO2.Firstly the preparation of Mn/TiO2 conditions were improved in this study. There are four aspects have carried on the optimized design, which was active component ratio, the precursor solution, calcination temperature and auxiliaries. All of the catalysts were prepared by the wet impregnation method, and select the best preparation of conditions through the analysis of the activity and the role of iron by BET,NH3-TPD,H2-TPR measurements finally.On this basis, three kinds of transitional metals were doped in Mn/TiO2 catalyst, such as Ce,Fe, Cu. By the analysis of the activity test, we found the catalytic efficiency significantly improved in the low temperature region, and relieved the declining effectively in the high temperature after Mn/TiO2 doped with the right amount of transitional metal. The results of XRD and BET indicate that doped with Ce. Fe, Cu not only increased the surface area, and larger the dispersion of the active component on the surface. It can provide more active sites in the reaction, which is useful to the proceeds. According to the XPS results, it can affect the surface of the valence states of Mn distribution, especially increased the content of Mn4+,Mn3+. The TPR spectra showed that the hydrogen consumption of doped catalyst was higher than Mn/TiO2 obviously. NH3-TPD and Py-IR results reveal that doping a fair amount of transitional metal can enhance the strength of Lewis and Bronsted acid, but can appear new Bronsted acid sites. It enhanced the acid sites of the surface greatly, and to improve the creativity of denitration.In order to select the best carrier, Mn/TiO2, Mn/TiNT and Mn/MCM41 three kinds of catalysts were used to test the denitrification activity. It was found that the activity of Mn/TiNT was the best at low temperature, the conversion rate of 70% was achieved at 100?,and the reactive temperature window was also wider, while the Mn/MCM41 catalyst is mainly expressed in good activity at high temperature. According to the TPR, BET, XPS, TPD and other characterization methods to study the different characteristics of different carriers, and using in situ infrared pyridine adsorption method to study the surface acid center of the three catalysts. Results showed TiO2 nanotube is the best carrier of SCR catalyst preparation, not only to make up the lack of specific surface area of TiO2 itself, and due to its rich Lewis acid sites, which greatly enhanced the surface acid amount of catalyst, It is conducive to improve the catalytic denitrification activity.Combined with the previous contents, select the low-temperature activity of Mn-Ce system, based on the addition of Cu and Fe, inspected the denitrification activity of composite catalysts through the experiment. In comparison, the best activity of Mn-Ce-Fe-Cu/TiNT was found, the conversion rate was above 70% at 100?300?,when 150? the conversion rate of NOx has achieve the maximum to 90.15%; The results of TEM, BET and XRD show that the active components are distributed evenly on the carrier of TiO2 nanotube, there is no phenomenon of sintering and serious agglomeration, so that the active components are amorphous; By TPR and XPS analysis, it was found that the catalytic oxidation-reduction ability was stronger, because of the mutual conversion between the electrons to promote the transfer of oxygen. Through the study of surface acidity found larger catalyst surface is rich in L-acid sites,it is conducive to the removal of NOx activity increased,the different temperature contrast found the amount of Lewis acid decreased with desorption temperature increment, and Bronsted acid content increased, the value of B/L increased, which is not only adverse for the low-temperature SCR reaction, but also the reason for poor high-temperature activity of Mn catalyst. |
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