Sb改性对Mn-Ce/TiO_(2)低温SCR催化剂性能的影响

Effect of Sb Modification on Mn-Ce/TiO_(2) Low-temperature SCR Catalyst

采用浸渍法分别制备Mn/TiO_(2)、Mn-Ce/TiO_(2)、Mn-CeSb/TiO_(2) 3种催化剂,考察了3种催化剂在低温90~220℃之间的活性和选择性,并利用BET (Brunauer-Emmett-Teller,BET)比表面积分析、扫描电镜(scanning electron microscope,SEM)、X射线衍射(X-ray diffraction,XRD)、傅里叶变换红外光谱(Fourier transform infrared spectroscopy,FT-IR)、X光电子能谱(X-ray photoelectron spectroscopy,XPS)、H2-程序升温还原(H2-temperature-programmed reduction,H2-TPR)和NH3-程序升温脱附(NH3-temperatureprogrammed desorption,NH3-TPD)对3种不同的催化剂样品进行了表征,分析影响选择性催化还原(selective catalytic reduction,SCR)活性的原因。当Sb/Mn=0.2时,Mn-Ce-Sb/TiO_(2)催化剂具有最佳活性,NOx转化率在120℃时达到94%,150℃时的NOx去除率达到98%,锑的掺杂同样提高了Mn-Ce/TiO_(2)催化剂的氮气选择性。BET和XRD表征结果发现Sb改性增大催化剂的比表面积,降低锰氧化物的结晶度,TPD和TPR发现Sb改性使得低温下的氧化还原能力增强,但对酸性位点没有大的影响。XPS结果表明锑的掺杂可以提高Mn-Ce-Sb40.2/TiO 2催化剂表面的吸附氧和Ce^(+)/Ce^(3+),这使得Ce^(4+)和Ce^(3+)之间的氧气储存和释放增强,同时化学吸附氧含量的增高,使得催化剂表面的氧迁移率提高,可以更好的促进NO转化为NO_(2)通过“快速SCR反应”提高反应活性。还检测到Sb的引入可以提高Mn^(4+)的含量,这同样使得NO去除率提高。探究Sb掺杂对催化剂抗硫性实验发现引入Sb后可以提高催化剂在低温下对SO_(2)的耐受性,150℃下反应8h其NOx转化率从98%降到81%,而且在停止通入SO_(2)后活性可恢复到97%。

In this paper,three catalysts,Mn/TiO_(2),Mn-Ce/TiO_(2) and Mn-Ce-Sb/TiO_(2),were prepared by the impregnation method.The activity and selectivity of these catalysts of low temperature at 90~220℃were investigated.By using Brunauer-Emmett-Teller (BET),scanning electron microscope(SEM),X-ray diffraction (XRD),Fourier transform infrared spectroscopy (FT-IR),X‐ray photoelectron spectroscopy(XPS),H2-temperature programmed reduction (H2-TPR),and NH3-temperature programmed desorption (NH3-TPD),the catalyst samples were characterized to analyze the factor affecting the selective catalytic reduction (SCR) activity.It can be found that when Sb/Mn=0.2,the Mn-Ce-Sb/TiO_(2) catalyst has the best activity,and the NOx conversion rate reaches 94%at120℃and the NO_(x) removal rate reaches 98%at 150℃.The same doping with antimony improved the nitrogen selectivity of the Mn-Ce/TiO_(2) catalyst.BET and XRD characterization results show that Sb modification increases the specific surface area of the catalyst and decreases the crystallinity of manganese oxide.TPD and TPR show that Sb modification enhances the redox ability at low temperatures with no major impact on acid sites.XPS results show that the doping of antimony can increase the adsorbed oxygen and Ce^(4+)/Ce^(3+) on the surface of the Mn-Ce-Sb0.2/TiO_(2) catalyst,which enhances the oxygen storage and release between Ce^(4+) and Ce^(3+) and chemically adsorbs oxygen at the same time.The increase in the content increases the oxygen mobility on the catalyst surface,which can better promote the conversion of NO to NO_(2) and increase the reaction activity through the"fast SCR reaction".It is also detected that the introduction of Sb can increase the content of Mn^(4+),which also increases the removal rate of NO.The experiment explored the effect of Sb doping on the sulfur resistance of the catalyst.It can be found that the introduction of Sb can improve the tolerance of the catalyst to SO2 at low temperatures.After 8hours of reaction at 150℃,the NOx conversion rate dropped from98%to 81%,and the introduction of SO2 was stopped after the activity was restored to 97%.