The Role Of Iron In Denitration Catalyst At Low Temperature And The Machanism Of Fe-V-W-Mn-Ce/TiO₂ Composite Catalyst

NO_x is one of the pollution gases in the atmosphere,NO is one of the main pollution gases in NO_x.NO_x can cause photochemical smog,ozon depletion and harm to human health.NH₃ selective catalytic reduction method is an effective method to remove NO from pollution gases.So,we investigated the De-NO_x activity and reaction mechanism of the catalysts we prepared to improve the commercial catalyst for NH₃-SCR reaction.A Fe-V-W-Mn-Ce/Ti O₂ catalyst was prepared by ultrasound-substep-wet impregnation method for removing NO_x from diesel engine exhausts and its excellent low-temperature selective catalytic reduction（SCR）activity over a broad temperature window of 150 ^oC-450^oC has been demonstrated.Two serious catalysts of Fe-V-W/Ti O₂ and Fe-Mn-Ce/TiO₂catalysts were also prepared.Fe（0.1）-V-W/TiO₂ and Fe（0.1）-Mn-Ce/TiO₂ catalysts with best content of iron were used to compare with Fe-V-W-Mn-Ce/TiO₂,V-W/TiO₂ and Mn-Ce/TiO₂catalysts to investigate the relationship between the performance and the activity,and the role of iron by BET,NH₃（NO）-TPD,H₂-TPR,XRD,XPS,FT-IR measurements.In addition,SCR reaction mechanism of Fe-V-W-Mn-Ce/TiO₂ catalyst was investigated using In situ DRIFTS measurment.And the reaction activation energy was also obtained in standard reaction.When the content of active component is moderate on the catalyst prepared by impregnation method,the active component could well dispersed on the surface,there only emerge anatase titanium oxide.But when too much content of iron loaded on the surface,there would generate Fe₃O₄ or Fe₂O₃ crystalline phase,destroy the dispersiveness.Catalyst surface atomic numbers on unit area and total atomic numbers can be calculated combined XPS and BET results.The BET surface area increased with the addition of iron,and further increase the total atomic number on the surface,while the atomic number on unit area decreased,this indicated that iron promoted the dispersion of the active components.Much active component well dispersed on Fe-V-W-Mn-Ce/Ti O₂ catalyst.To explore the redox properties of the catalyst,H₂-TPR measurement was taken.According to the H₂-TPR results,the reduction temperature of the catalysts with iron are lower than the catalysts without iron,which indicated that the redox properties improved by the addition of iron.The reduction peak of Fe-V-W-Mn-Ce/TiO₂ catalyst much larger than other catalysts,and exhibit well redox properties.NH₃-TPD and In situ DRIFTS measurments were combined to explore the information of acid sites.It was found that much acid sites exist on Fe-V-W-Mn-Ce/TiO₂catalyst surface.This maybe the reason of Fe-V-W-Mn-Ce/TiO₂ catalyst owns broad temperature window.Finally,we explored the influence of The valence state of catalyst surface elements to the catalystic activity.moderate ratio of V⁴⁺/V⁵⁺and(Mn²⁺+Mn³⁺)/Mn⁴⁺in favour of the De-NO_x activity,the ratio of V⁴⁺/V⁵⁺and(Mn²⁺+Mn³⁺)/Mn⁴⁺more close to1.0,the better activity the catalyst owns.This was because the ratio of low state and high state close to 1.0 is best for keeping blance of reduction rate and oxidation rate.The redox elements exist as V⁵⁺,V⁴⁺,Mn⁴⁺,Mn³⁺,Mn²⁺,Fe³⁺,Fe²⁺pairs on the surface,such redox electron pairs exhibit excellent redox ability potential higher than the inserting O species and they also can facilitate electron and oxygen transfer.According to NO-TPD experiment,we found much NO adsorbed on the surface,and took part in the SCR reaction.And in situ DRIFT measurement was used to explore the reaction path.Both E-R mechanism and L-H mechanism exist on Fe-V-W-Mn-Ce/TiO₂catalyst,many reaction path may occurred.We also cacluated Ea of the standard SCR reaction on the catalyst.The reaction activation energy was much lower than the commercial catalysts which indicated the SCR reaction was easier happened on Fe-V-W-Mn-Ce/TiO₂ catalyst.