| Nitrogen Oxides(NOx) emission, which mainly brings about air pollution in China, has been causing many environmental problems, such as photochemical smog, PM 2.5 etc. The selective catalytic reduction(SCR) of NOx with NH3 is the remediation technology most widely used for removing NOx from the flue gases of power boilers and industrial furnaces. However, the SCR catalysts have high manufacturing costs and bad performance of NO removal at low temperature. Therefore, it is necessary, to develop cheap but efficient low temperature SCR catalyst.In this study, it was investigated how the catalytic performances of three kinds of low-temperature SCR catalysts, separately supported on H2O2 modified activated carbon, nitrogen-doped TiO2 and amino-modified mesoporous silicon, were influenced with respect to modification method of support, the loading method, preparation technology and process parameter optimization. The prepared catalysts have been systematically studied by using scanning electron microscope(SEM), specific surface area( BET), Fourier Transform Infrared Spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS) and X-ray diffraction(XRD).(1) It is concluded that soaking activated carbon in hydrogen peroxide for 2 hours is the best modification method; A contrastive study was made on MnOx/AC and CuO/AC which were separately prepared by ultrasonic impregnation and precipitation impregnation methods. The results showed that the catalyst prepared by precipitation method had a better activity. MnOx/AC with 5% MnOx loadings and calcinated at 400℃ exhibited better activity, nearly 70% NO conversion could be obtained at 180℃.(2) N-doped TiO2 carrier was prepared by means of sol-gel method, then Mn, Cu and Ce were loaded through new coprecipitation method, coprecipitation method and equivalent traditional impregnation method on N-doped TiO2. The results showed that the new coprecipitation method is the best loading method. N doping can significantly enhance the denitrification efficiency and the best ration of titanium to nitrogen is 1:3. Based on its catalytic performance evaluation, it was found that catalyst obtained 98.7% NO conversation under 500 ℃, at space velocity of 18,000 h–1 with the ammonia-nitrogen ratio of 1:2.(3) The surface appearance morphology, physical properties, spectral characteristics and structure and physicochemical properties such as element property and crystal structure of catalysts were characterized respectively by SEM, BET, FTIR, XPS and XRD. The results showed that N doping had almost no effect on the specific surface area and surface topography characteristics of the catalysts; N doping has caused a series of changes on catalyst structure and surface properties in this way that N gets into TiO2 crystal lattice and replace part of oxygen in the lattice, and exists in the form of Ti-N key in titanium dioxide lattice, resulting in great increase in the catalyst surface oxygen vacancies, so that the ability of oxygen adsorption, superoxide radical concentration have increased, thus improved the redox ability on the catalyst surface.(4) A novel double cone rod-shaped mesoporous hexagonal silicon single crystal was synthesized with low ammonia and surfactant concentration. The study results indicated that the size of mesoporous silicon single crystal was controlled through adding inorganic salts in the ammonia system, maintaining good hexagonal shape in the case of an aspect ratio increases, the largest single crystal size is about 10 μm. The relationship between genetics and surface was exploited and the related mechanism was analyzed. Under the premise that the mesoporous silica morphology was successfully controlled, amination was modified, resulting in reducing the amount of ammonia in denitration reaction, so that the production cost in actual use was reduced.(5) According to the reaction mechanism Eley- Rideal, a first-order kinetic model suitable for the low temperature SCR denitration catalyst in this experiment was established, and it was calculated that the catalyst reaction activation energy was 99.13 KJ/mol, pre-exponential factor was 3.41 x 108 s- 1(mol·cm-3).(6) A new type of low-temperature SCR catalyst for industrial application was developed by using a combination of above results(modification through dipping in H2O2, loading through new coprecipitation, synthesis of mesoporous silicon and amination modification).Activity evaluation clarified that this type of catalyst exhibited good catalytic activity between 180-250°C. The NO removal reached 92% under conditions that SO2/SO3 conversion rate is less than 1%, and ammonia escapement ratio is less than 3 ppm. |
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