Hydrothermal Aging And Washcoating Property Of Zeolite NH₃-SCR Catalyst And Optimization Of Mn/Ti Catalyst

Nitrogen oxides（NOx）,emitted during combustion of fossil fuels,are considered to be environmental pollutants associated with the greenhouse effect,acid rain,and photochemical smog.Due to the motor vehicle is the most serious pollutant source,the related NOx abatement technology attracts global researcher’s attention.Due to the advantage of high NOx conversion ratio,wide operating window and low cost,Selective catalytic reduction（SCR）of NO with NH₃ are deemed as the most promising technology for large-scale commercial applications in exhaust gas aftertreatment field.Low temperature activity,hydrothermal deactivation and washcoating are the most important research topics in SCR catalysts and related productization process.In this paper,three topics list in last paragraph were discussed one by one.At first,hydrothermal aging condition with different temperature were applied on commercial zeolite NH₃-SCR catalysts,related evaluation and characterization results were compared,and different impact of aging temperature on different catalysts was discussed.Then,washcoating with different binder was applied on zeolite catalysts,the performance and mechanism was compared and discussed.Last but not least,due to the insufficient low temperature activity of Fe-BEA and Cu-SAPO,Mn-Fe/W-Ti system catalysts with superior low temperature activity was developed,RSM method and characterization was applied to investigate the correlation model among Mn,Fe,W loading ratio,low temperature activity and high temperature selectivity.The results showed:（1）Hydrothermal aging pretreatment was applied on Fe-BEA and Cu-SAPO zeolite commercial catalysts with different temperature.The evaluation result showed that the influence of hydrothermal deactivation was not the same in different temperature range.Two-steps model among aging temperature,activity reduction and inner mechanism was built.For the samples aging in700 or 800°C,surface oxygen species,surface acidy site and oxidation capacity was decreased.For the samples aging in 900°C,micro-structure of catalyst collapsed,which leaded to the decrease of BET surface area.（2）Performance of different binder used in washcoating process for Fe-BEA and Cu-SAPO was compared.The AlOOH and ZrO（NO₃）₂ was conformed as great binder.Then,the BET,XRD and SEM of powder mixture samples were compared,it could be seen that the different binder transform to different scale particles to bind catalyst together.（3）From the Mn/Ti system,the activity of different supported bases,different loading ratios and different bimetallic components were compared.Mn-Fe/Ti system showed the most superior low temperature activity.Then,W was introduced to enhance high temperature N₂ selectivity.With the co-addition of W and Fe,the Mn-Fe/W-Ti catalysts showed great low temperature activity and wide operating window.（4）The response surface method was applied to build model about the correlation among Mn-Fe total loading ratio,Mn relative ratio,W loading ratio,low temperature activity and high temperature selectivity.Then,the model was used to investigate the best ratio,which could achieve highest activity and selectivity.（5）XRD,BET,H₂-TPR,NH₃-TPD and XPS was applied to investigate the influence of W and Fe addition on Mn/Ti system,the results indicated that activity improvement might be contributed to the increase of manganese species valence and surface acid sites due to co-addition of iron and tungsten.