Study On Preparation And Performance Of Ferrum Base And Ceria Base Catalysts For The Oxidation Of NO_x By Catalytic Ozonation

In recent years,smog has become increasingly serious in China,and the emission of nitrogen oxides is one of the reasons for its formation.The nitric oxide makes up the majority of nitrogen oxides.The flue gas temperatures of industrial furnaces,sintering machine and catalytic cracking unit are too low to be used in the selective catalytic reduction(320-400?).To achieve low-cost flue gas denitrification,the simplest method is to oxidize nitric oxide to soluble nitrogen oxides,and then be absorbed with alkali solutions.Due to the weak oxidizing ability of O3,NO is mainly converted into NO2.However,the NO2 absorption was unsatisfactory.Thus,it is necessary to convert O3 into stonger oxidants,oxidizing NO and NO2 into nitrates and nitrites to facilate the further absorption.In the present study,the catalytic ozonation for denitrification ranging from 40 to 180 ? was proposed,and the corresponding catalysts were put forward.The oxidation denitrification method can not only be used for the low-temperature flue gas,but also be used for ultra clean emissions after conventional desulfurization process in thermal power plant boiler.Firstly,O3/H2O2 advanced oxidation method was proposed for oxidizing NO and NO2 into nitrates and nitrites.There is a strong synergy between O3 and H2O2,which produces hydroxyl radicals and superoxide radicals simultaneously.Superoxide radicals could selectively react with NO to generate HNO3 with a fast rate constant;hydroxyl radicals could non-selectively react with NO or NO2to form HNO2or HNO3also with a fast rate constant.The test results showed that when the flue gas temperature was 80 0C,the molar ratio of H2O2/O3 was 0.8,the O3 concentration was 0.5 mg-L-1 and the NOx concentration was420 ppM,the oxidation efficiencies of NO and NO2into nitrates and nitrites achieved up to 68%,which was 60%higher than O3/H2O mehod and 58%higher than H2O2oxidation method.Secondly,a-FeOOH catalysts were syhthesized by hydrothermal method,precipitation-hydrolysis method and oxidation-hydrolisis method.The effects of different preparation methods on the physical and chemical properties and catalytic ozonation performance of oxidizing NO and NO2were investigated.The test results indicated that when the flow rate of H2O was 0.4mL·min-1,o3concentration was 1.3mg·L-1,NOx concentration was 460 ppm and the flue gas tempetature was 40?,the oxidation efficiencies of NO and NO2 were 85.6%,75.8%and 70.7%for the a-FeOOH catalysts prepared by hydrothermal method,precipitation-hydrolysis method and oxidation-hydrolisis method.The a-FeOOH prepared by hydrothermal method had the largest BET surface area and the largest number of Fe-OH,both of which were beneficial for ·OH production,thus presenting the highest activity.Additionally,RGO-CeO2 composite catalyst was prepared by hydrothermal method using reduced graphene oxide(RGO)as support,and it was used to oxidize NO and NO2 by catalytic ozonation.The test results demonstrated that the RGO improved the dispersion of CeO2,and promoted the electron transfer from support to CeO2,thus increasing the number of reduced state of Ce3+ ions and oxygen vacancies.The increased nuUber of Ce3+ and oxygen cacancies was conductive to the absorption of H2O and the activation of O3,thus improving the catalytic activity.When the flow rate of H2O was0.1 mL·min-1,O3concentration was 1.3 mg·L-1,NOx concentration was 460 ppm and the flue gas temperature was 40?,the oxidation efficiency of NO and NO2was 95.6%under the catalysis of RGO-Ce0O2.Compared with O3/H2O,the oxidation efficiency was increased by 27.3%.Thirdly,based on the theory that metal-doped solid solution catalyst is conductive to the improvement of redox properties and the defect production,a series of Ce0.90Co0.10O2-?,Ce0.90Cu0.10O2-? and Ce0.90-xCuxCo0.10O2-? with different Cu2+ doping concentration catalysts were synthesized and utilized for oxidizing NO and NO2 into nitrates and nitrites by catalytic ozonation.The test results demonstrate that the appropriate Cu2+doping concentration not only promoted the generation of extrinsic oxygen vacancies,thus being beneficial for the absorption of H2O on catalyst surface;but also improved the oxidbility of catalyst and promoted the production of briging hrdroxyl groups,thus enhancing catalytic activity.When the flow rate of H2O was 0.1 mL·min-1,O3 concentration was 1.3mg mg·L-1,NOx concentration was 460 ppm and the flue gas temperature was 40?,the catalytic activity of Ce0.83Cu0.07Co0.10O2-? achieved the highest,attaining 96.7%,which was a little higher than RGO-CeO2.Finally,based on the thinking that doping modification promotes the production of surface defects and support loading benefits for the generation of active sites,Mn-Ce-O supported on anatase phase,monoclinic crystal phase and mixed crystal phase TiO2catalysts were synthesized and were applied to catalytic ozonation for oxidizing NO and NO2 into nitrates and nitrites.The characterization of catalysts show that both Mn-Ce/TiO2(AB)and Mn-Ce/TiO2(B)had high concentrations of surface-OH groups and oxygen vacancies,thus being beneficial for·OH production.However,Mn-Ce/TiO2(AB)promoted the redox reaction of Ce3+?Ce4+?Ce3+,which was more favorable for the generation of ·OH radicals.Thus,the catalytic activity of Mn-Ce/TiO2(AB)was the highest.When the NOx concentration was 210 ppm,O3concentration was 0.6mg·L-1 and the flue gas temperature was 40?,the catalytic activity of Mn-Ce/TiO2(AB)achieved 91.1%,which was 50.8%higher than O3/H2O method.Moreover,after 500 ppm SO2 was introduced,the oxidation efficiency of NO and NO2 of Mn-Ce/TiO2(AB)decreased by only 4.7%,showing a better SO2 resistance ability.