| How to manage nitrogen oxides scientifically and effectively has become one of the most urgent tasks in the field of air pollution control in China.The selective catalytic reduction of NO by NH3(NH3-SCR)is one of the most important technologies for flue gas denitrification.The TiO2 has excellent anti-SO2 poisoning properties and strong interaction between the active species(metal,metal oxide)when it plays as a support,so it is widely used as a support in the NH3-SCR catalyst.This paper focuses on the role of TiO2 crystal plane effects in the NH3-SCR reaction.Through a variety of physicochemical characterization methods,the influencs of the difference in exposed crystal plane structure of TiO2 on the existence state of active species CuO and the reason for the difference in NH3-SCR reaction performances were explored in detail.Based on the above studies,we further studied the physicochemical properties of TiO2 supported CuO with different ZrO2 doping on different exposed crystal faces and the influence of NH3-SCR reaction performance.The specific research content is as follows:(1)TiO2 supports with different morphologies and exposed crystal planes({101} and{100})were prepared,CuO was loaded with a dispersion capacity of 0.6 mmol/100 m2 TiO2,and the difference in the NH3-SCR catalytic activities were investigated.It was found that CuO/TiO2 catalysts with different exposed crystal planes have significant differences in NH3-SCR activity.Below 325 ℃,the NH3-SCR activity of CuO/TiO2-NOs samples with {101} facet exposed was better than that of CuO/TiO2-NRs samples with {100} facet exposed.At above 325 ℃,the order of activity was reversed.After a series of physical and chemical characterizations,it was found that the dispersed CuO occupies a tetrahedral vacancy on the TiO2 {101}surface to form an unstable 4-coordinated structure,which caused the electrons to migrate to the Cu species and the electronic interaction between the CuO and the TiO2 {101} surface was stronger,and there might be a redox cycle of Cu2++Ti3+←→Cu++Ti4+,which brought more acid sites,resulting in higher NH3-SCR activity at low temperature;At high temperature,a large number of nitrate species adsorbed on the surface of the catalyst occupied active sites,making the activity of NH3-SCR significantly lower.CuO occupied octahedral vacancies on the TiO2{100} surface to form a stable 6-coordinated structure,which made the catalyst has less acidic.Besides,large amounts of NH4NO3 were generated on the surface,and thus it exhibited lower NH3-SCR activity(50 ℃-250 ℃).while at high temperatures(250℃-450 ℃),the NH4NO3 would decompose,which could increase the activity.the TiO2{100} surface itself has more surface lattice oxygen,which can activate NH3 to form NxOy.Therefore,at higher temperature(400-450 ℃),the activity decreases(2)ZrO2 doped different morphologies of TiO2 were prepared,and the prepared material still had a specific exposed crystal plane.ZrTiOx was used as the support to support CuO.The influence of Zr doping on the NH3-SCR activity was studied.It was found that the activity of CuO/Zr0.05TiO2-NOs was lower than that before Zr doping,but the activity of CuO/Zr0.05TiO2-NRs was higher than that before Zr doping.The physicochemical properties of the catalysts were systematically characterized by XRD,Raman,TEM,H2-TPR,NH3-TPD,in-situ DRIFTS.It was found that Zr existed in different states in TiO2 with different exposed crystal facets.For the TiO2 {101},Zr could be well incorporated into the crystal lattice to form Ti-O-Zr,which could inhibit the growth of TiO2 crystal grains and increase the specific surface area.For the TiO2 {100},Zr was easy to segregate to the surface,and even form the crystal phase ZrO2 on the {100} surface of TiO2.The doping ofZr in TiO2 {100} would form a large amount of Ti3+ on the surface.After CuO was loaded,more Cu+ would be formed,forming a Cu2+ + Ti3+←→ Cu+ + Ti4+ cycle,increasing the surface acidity and increasing the surface acidity,and increasing NH3-SCR activity.The doping of Zr4+ would decrease the content of Cu+ and Ti3+,weaken the interaction between Cu and Ti,weaken the surface acidity,and eventually caused a drop in the NH3-SCR activity. |
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