Performance Studies Of No Reduction With C₃H₆ Over Porous Clay Heterostructures Materials Modified With Fe（Cu） Catalysts

In recent years,the demand of fossil fuels such as coal,oil and natural gas has grown substantially in the world under the accelerated process of industrialization.However,large quantities of pollutants are released to the atmosphere from the combustion of fossil fuels,especially nitrogen oxides（NO_x）.Nitrogen oxides are the source of ground level ozone,acid rain and eutrophication,as well as directly harmful to the health of humans.Many kinds of hydrocarbons are present in the exhaust and many of them can represent a supplementary source of pollution,while a concomitant removal of these pollutants by reduction of NO appears attraction.Thus,selective catalytic reduction of NO by hydrocarbons（HC-SCR）as a potential technology for flue gas DeNO_x has been widely concerned by researchers.Traditional pillared clays（PILCs）modified with iron were useful in catalytic reduction of NO by propylene.However,the catalytic activity of this type of catalyst still needed to be improved,because the NO removal efficiency had significant decrease in the presence of oxygen.Based on this research,we chose new porous clay heterostructures materials as support and prepared Fe-PCH catalyst for NO reduction by propylene.Copper was introduced into Fe-PCH catalyst as a second modified metal to prepare CuFe-PCH catalyst,which has higher NO removal efficiency in C₃H₆-SCR and lower reactive temperature window.The obtained samples were characterized and measured by plasma emission spectroscopy（ICP）,N₂adsorption-desorption,X-ray diffraction（XRD）,ultraviolet diffuse reflectance spectroscopy（UV-vis）,scanning electron microscope analysis（SEM）,transmission electron microscope（TEM）,thermogravimetric analysis（TGA）,programmed temperature reduction analysis（H₂-TPR）,pyridine adsorption infrared spectroscopy（Py-IR）,and O₂ programmed temperature desorption（O₂-TPD）to explore the metal content,preparation method,reactive condition and H₂O/SO₂ influence on catalytic properties.Based on in situ diffuse reflectance infrared Fouier transform spectroscopy（DRIFTS）technology,the reactive intermediates formed during C₃H₆-SCR were detected,and a reasonable reaction pathway and mechanism were proposed.Specific contents are as follows:1.A series of Fe-PCH catalysts were prepared by ion exchange or impregnation method for selective catalytic reduction of NO by propylene.The results showed that Fe-PCH prepared by impregnation had higher C₃H₆-SCR catalytic activity.The best Fe loading was 8.4 wt.%.8.4Fe-IMP catalyst sample performed 96%NO conversion at 400°C and 100%NO conversion at 450°C.2.Through systematic and comprehensive catalyst characterization analysis,the effects of preparation methods and iron loading on the texture characteristics,active species morphology,crystallinity,redox performance,surface acidity,and NO catalytic reduction performance of Fe-PCH catalysts were studied.The results showed that the formation ofα-Fe₂O₃ nanorods crystals over the surface of Fe-PCH catalyst were the main active species in C₃H₆-SCR.The exposed（110）and（104）crystal planes had higher Fe atom density,which was beneficial to the formation of Lewis acid sites and adsorption of NO.In situ DRIFTS results showed that inorganic nitrate species,acetate species,nitrogen-containing organic intermediates,and isocyanate species were the main intermediates in C₃H₆-SCR over Fe-PCH catalyst.3.The effects of reaction conditions on C₃H₆-SCR over Fe-PCH catalyst were systematically studied.Increasing the propylene concentration within a certain range could promote the catalytic performance of NO removal.And high NO concentration in the reactive atmosphere caused a decrease in NO conversion.Fe-PCH catalyst could also reach high NO removal efficiency under high GHSV.Note that high oxygen concentration in the reaction atmosphere affected a lot on the catalytic reduction performance of Fe-PCH.In situ DRIFTS studies showed that the increasing oxygen concentration promoted the adsorption process of C₃H₆ and NO.However,oxygen compounds（C_xH_yO_z）were seriously consumed by oxygen,which inhibited the formation of isocyanate（-NCO）species,leading to decrease in NO removal efficiency.4.The introduction of Cu into Fe-PCH as a second modified metal was effective to improve the catalytic activity and reduce the reactive temperature.The CuFe-PCH catalyst with 1:1 molar ratio of Cu and Fe showed the best C₃H₆-SCR catalytic performance.The maximum NO conversion could reach 58.5%at 300°C in 0.1%C₃H₆,and reach 100%at 350°C in 0.3%C₃H₆.CuFe-PCH catalyst was beneficial to the formation of isocyanate species（-NCO）,which were important in C₃H₆-SCR,to improve the efficiency of NO reduction by propylene.5.The effects of H₂O and SO₂ on C₃H₆-SCR over CuFe-PCH catalyst were systematically studied.Although CuFe-PCH catalyst exhibited well in water resistance,the interlayer pores and clay laminate structure of the catalyst were destroyed after high-temperature hydrothermal treatment,which led to a decrease in the catalytic performance of NO reduction.SO₂ in simulated flue gas caused irreversible poisoning of CuFe-PCH catalyst,when sulfates covered active sites.As a result,SCR reaction temperature window would shift to the higher temperature.