Study Of MnO_x/Al-SBA-15for Low Temperature Selective Catalytic Reduction Of NO_x In Waste Incineration Flue Gas

Waste incineration has became one of the important technologies in municipalsolid waste （MSW） treatment, but it produces a variety of secondary pollutants. NO_x,as one of the major pollutants, which would cause acid rain, photochemical smog,global warming, ozone layer damage and the other environmental problems, it hascaused the people’s extensive concern. SNCR/SCR technology combines SNCR andSCR technology advantages, it need less investment, lower operating cost and hashigher efficiency and safety, especially suitable for our country’s relatively weakeconomic conditions, will become the preferred technology in our country’s wasteincineration flue gas denitration. Generally, the SCR unit of SNCR/SCR technologyin refuse incineration power plant located downstream of the the desulfurizer andbag filters, and the temperature of flue gas was below150℃after bag filters.However, the current commercial catalyst V2O5-WO3（MoO3）/TiO₂, which hasnarrow temperature window for300⁴00℃, and it can not achieve ideal effect ofNO_x removal in low temperature （<200℃）. Therefore, the key of this dissertation isto develop a kind of low temperature and high active SCR catalyst which suitable forwaste incineration flue gas denitration.A series of MnO_x/SBA-15and MnO_x/Al-SBA-15was prepared by post synthesismethod, further structure characterized by N₂adsorption-desorption, XRD, Raman,TG、XPS、NH₃-TPD and FT-IR as well as activity test for SCR reaction. And thereaction process on catalysts surface was studied by DRIFT analysis.The results showed that the catalyst with acetyl acetone manganese as precursor,10%Mn contents and400℃calcined temperature has the highest SCR activity, theNO_xconversion was about80%at150℃, and reached94%at200℃. Three states ofmanganese species （MnO₂, Mn3O4, and Mn2O3） coexisted on MnO_x/SBA-15catalysts,MnO₂was the main active phase.The doped material MnO_x/Al-SBA-15catalysts maintained high surface area,large pore volume, uniform pore size, and MnO_xwas highly dispersed with on catalysts surface. In addition, Al would increase the concentration and the valence ofMn, improve the catalysts surface acid. The MnO_x/Al-SBA-15catalyst with Si/Al=50had the highest activity, the NO_xconversion was96%at150℃, and nearly100%at180℃. Due to the high dispersion of MnO_xand the stronger surface acidity, theMnO_x/Al（50）-SBA-15catalyst exhibited higher SCR activity.The in situ DRIFTS results revealed that coordinated NH₃and NH4+coexisted oncatalysts surface, coordinated NH₃was the main states of NH₃in SCR reaction. Afterdoping Al, NH₃active site increased, both kind of NH₃adsorption state would react withthe gas-phase NO and adsorptive NO. Among the NO adsorption species, nitriteactivity was highest, could rapidly react with surface adsorptive NH₃species, butbidentate nitrate species occupied the catalyst active site, it was adverse to SCRreaction. Besides, the SCR reaction on MnO_x（10%）/SBA-15catalyst surface werecoordinated NH₃and adsorptive NO, belonged to the L-H mechanism, while doping Al,gas-phase NO could also recat with adsorptive NH₃on the MnO_x（10%）/SBA-15catalyst surface, L-H mechanism and E-R mechanism coexisted.