Study On Low Temperature Denitrification Of Mn-Ce/ETS-10 Catalysts

Based on the study of NH₃-SCR activity of Mn/ZSM-5,Mn/USY and Mn/ETS-10 catalysts,we selected the ETS-10 molecular sieves preferentially with excellent low temperature denitri-fication activity,and studied the effects of Mn and Ce loaded on the desulfurization activity of Mn/ETS-10 and Mn-Ce/ETS-10 catalysts at low temperature systematically.The physical and chemical properties of the catalysts were analyzed by means of SEM,TEM,BET,XRD,H2-TPR,NH₃-TPD and Py-IR.Simultaneously,the vapor and SO2 resistance of the catalysts under differ-ent Mn and Ce loading conditions was investigated,based on the preferential selection of 5%Mn/ETS-10 and 5%Mn-1%Ce/ETS-10 catalysts,the physical and chemical properties of the catalysts resistance and SO2 poisoning mechanism were analyzed by SEM,XRD and FT-IR.The main conclusions are as follows:?1?Compared with Mn/ZSM-5 and Mn/USY catalysts,the low temperature SCR activity of Mn/ETS-10 was the most efficent,and the NH₃-SCR activity in 5%Mn loading was the high-est in Mn/ETS-10 series,the highest NO conversion efficiency appeared at 160?,reached to 93.8%.The addition of Ce contributed to the activity of the Mn/ETS-10 catalysts and broaden the temperature window of the catalysts activity;1%Ce has the better NH₃-SCR activity than the remaining Ce loading,the NO conversion efficiency of 5%Mn-1%Ce/ETS-10 catalyst reached at 100%in 160-200?.?2?SEM and TEM characterizations showed that the prepared molecular sieve samples had a unique morphology for the regular quadrangular pyramidal structure;the BET surface shows that the prepared samples had a large specific surface area.When loaded Mn,the specific surface area of the catalysts was decreased,and active component Mn loaded on the surface blocked the partial pore of the ETS-10.The XRD results showed that the prepared samples have typical ETS-10 diffraction peaks,XRD tests on the catalyst samples loaded with Mn showed that the active components of the MnOx were uniformly dispersed on the surface of the ETS-10 carrier,and no obvious MnOx crystals were formed.The prepared catalyst samples were subjected to H2-TPR tests,and found that with the increase of the loading of active components,the redox capacity of the catalysts is enhanced,and the redox capacity is reduced when the loading is large,the 5%Mn/ETS-10 has a relatively good redox capacity.Ce-loading made MnOx species reduction peak temperature reduced,showed that there is a strong affection between MnOx species and CeO2 species to promote each other,which can enhance the low temperature SCR activity of catalysts.NH₃-TPD results showed that,in the NH₃-SCR reaction of Mn/ETS-10 serial catalysts,the acid content of weak and medium acid was more able to dominate the activity of SCR,the higher the active components loading,the greater the acidity of the catalysts surface.In the 5%Mn-x%Ce/ETS-10 serial catalysts,weak acid is the key factor affecting the activity of NH₃-SCR,and the weak acid sites are more favorable for the activity of low temperature SCR.Py-IR characterizations indicated that Lewis acidity was the key factor affecting the adsorption process of NH₃,and the NH₃-SCR activity of ETS-10 serial catalysts was determined.?3?Effects of craft conditions:the NO removal efficiency of Mn/ETS-10 was the highest after calcined at 550?.When different types of active component load,the acidity of catalysts and acid content changed.The acidity of the ETS-10 after loading Sr and Ni contents was changed,which affected the low temperature SCR activity.Too small or too large space velocity are not conducive to SCR reaction,in this experiment,the NO removal efficiency was relatively good with 37000b-1 space velocity.When the NH₃/NO ratio was 1.1 and the oxygen content was 5 Vol%,the NH₃-SCR activity of the catalysts at 160? was the best.?4?The NH₃-SCR mechanism of the ETS-10 molecular sieve supported Mn-Ce can be con-sidered to be:the NH₃ first adsorbed with the Lewis acid sites on MnO2 and formed the NH4+species,this species could react with NO to form intermediate NH2NO species,which was then decomposed into N2 and H2O.The activity of Lewis acid on the surface of catalysts was much higher than that of Bronsted acid,and the ability of the weak acid is larger than that of strong acid.When the specific surface area is within a certain range,the specific surface area has little effect on the activity of NH₃-SCR.?5?Mn/ETS-10 and Mn-Ce/ETS-10 serial catalysts showed that the NH₃-SCR denitrifica-tion activity decreased first and then slowly recovered before and after existing H2O?g?or SO2,but could not reach the initial NO removal level.Mn/ETS-10 and Mn-Ce/ETS-10 serial catalysts have better resistance to SO2 than those with weak water vapor resistance?SO2 concentration of 500ppm and H2O?g?content of 5%?,and the water resistance of the catalyst was better because titanium-silica molecular sieve itself is unique in its structure and properties;5%Mn/ETS-10 and 5%Mn-1%Ce/ETS-10 catalysts showed better resistance than other catalysts in the same series.The NO conversion of 5%Mn/ETS-10 decreased with time increasing in SO2 atmosphere,SO2 recovered to 89.4%after 1 h removal,and 5%Mn-1%Ce/ETS-10 was changed in SO2 atmos-phere over time,suggesting that Ce produced some kind of SO2 induction.After adding 1%Ce,the 5%Mn/ETS-10 catalyst had a significant increasement in anti-SO2 poisoning ability.?6?The results of SEM,XRD and FT-IR showed that the white granular material can gen-erate on the surface of catalysts in the SO2 atmosphere,which may be ammonium sulfate species.The addition of Ce can form Mn-O-Ce community with Mn,which promotes the resistance of the catalysts,SO2 poisoning performance.In this thesis,one of the main toxic mechanisms of SO2 in Mn-Ce/ETS-10 catalysts was that NH₃ was adsorbed on the catalyst to form NH4+ species and reacted with acidic SO2 to form ammonium sulfate or ammonium bisulfate.The NH₃-SCR activity of Mn-Ce/ETS-10 catalysts was affected by the accumulation of ammonium salt ions on the surface of catalysts and covering the active sites of the catalysts.