| Now selective catalytic reduction with NH3?NH3-SCR?is the dominant commercially technology to remove the nitrogen oxides from stationary sources,with advantages of high stability and efficiency.Catalysts are the crucial factor for the NH3-SCR technology,and the most commercially used catalysts V2O5-WO3?MoO3?/TiO2,have a relatively narrow and high temperature window,low N2 selectivity at high temperatures and the toxicity of vanadium to the environment.Therefore,development of highly active and environmentally-friendly low-temperature NH3-SCR catalysts is very important to the enviroment,social and economic development.In recent years,highly active low-temperature NH3-SCR catalysts are continually being developed.However,the low temperature SCR catalysts would be easily deactivated by SO2 and H2O which would not be useful under actual working conditions.Therefore,enhancing the SO2 and H2O resistance of these catalysts is significant in the practical application of low-temperature SCR technology.While the Ce modified SCR catalysts presented better SO2 tolerance and H2O resistance,which attributed to Ce with better excellent oxygen storage and transfer capacity to improve the redox ability of the catalysts.Meanwile Ce were sulfated preferentially in SO2-containing gases and inhibited the deposition of ammonium sulfates and prevented the formation of metal sulfites/sulfates.In this work,based on manganese have high active and SAPO-34 molecular sieve with adjustable surface acidity and superior specific area properties,cerium was incorporated in the SAPO-34 framework by a one-step hydrothermal method and supported on the surface by Ethanol dispersion method,respectively,to investigated the effect of cerium exist in the framework and the surface resistance to SO2 and H2O in the low-temperature NH3-SCR.Firstly,cerium was incorporated in the SAPO-34 framework by a one-step hydrothermal method,the amount of the template and the cerium content were investigated.when DIPA/P2O5 ratio was 3.0 and Ce/P2O5 ratio was 0.3,the sample showed the high crystalline in the CeAPSO-34 molecular sieves,and the results of the EDS analysis showed that the insertion of Ce into the SAPO-34 framework.Mn/CeAPSO-34 was prepared by the Ethanol dispersion method.When the loading of Mn was 15 wt.%and the calcination temperature was 400°C,the catalyst showed the best NH3-SCR activity at the reaction temperature range.And Mn-Ce/CeAPSO-34 was prepared by the Ethanol dispersion method.The catalyst showed the best NH3-SCR activity and high N2 selectively at low temperature when Ce/Mn ratio was 0.4.Nearly 97.7%NOx conversion over the catalyst occurred at 140°C and remained about 100%in the temperature range of 160-240°C.The effects of SO2 and H2O on SCR activity of the catalysts at 180°C was investigated.In the presence of 0.01%SO2,10%H2O or 0.01%SO2+10%H2O,the NO conversion for Mn-Ce/CeAPSO-34?decreased to 88%,89.08%and 65.45%?is much higher than Mn-Ce/SAPO-34?decreased to 67%,76.94%,and 42.16%?,Mn/CeAPSO-34?decreased to 56%,68.1%and 40.29%?and Mn/SAPO-34?decreased to 16.9%,36%and 13.28%?,indicating that a strong synergistic effect existed between cerium in the framework and the surface which presented outstanding SO2 tolerance and H2O resistance.Secondly,to investigate the mechanism of the synergistic effects of cerium exist in the framework and the surface,the in situ Fourier translation infrared spectrum?FT-IR?was used to study the behavior of the formed active intermediates and surface species over Mn/SAPO-34,Mn/CeAPSO-34,Mn-Ce/SAPO-34 and Mn-Ce/CeAPSO-34 in the presence of SO2 at low temperature NH3-SCR.The in situ FT-IR spectrum revealed that the strong synergistic effect would be beneficial to more nitrate species and NH3 species adsorbed on catalysts surface,and inhibit the deposition of sulfate species over Mn-Ce/CeAPSO-34.Meanwhile,the mechanism of NH3-SCR of NOx with SO2 on the catalysts at 180°C both takes place via L-H and E-R mechanism.Finally,based on the Density Functional Theory,build the catalysts microstructure model of Mn-Ce/CeAPSO-34 and optimized the structure in a stable state.While simulated the adsorption behavior of nitric oxide,ammonia,sulfur dioxide and water over the catalysts and calculated the adsorption energy of the transition states in the NH3-SCR,to investigated the synergistic effects of cerium exist in the framework and the surface resistance to SO2 and H2O in the low-temperature NH3-SCR and the reaction mechanism.The theoretical results imply that the synergistic effect could be attributed to the[-Ce-O-Ce-]units,which means Ce site supported on the surface neighbored by Ce site in the framework would be beneficial to the reaction with SO2 and H2O.Meanwhile the units were capable of reacting with NO and NH3. |
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