Research Of Preparation,Characteristic And Performance For Cu-CHA Zeolites And Its Monolithic SCR Catalyst

Nitrogen oxides（NO_x）,a major component of atmospheric pollutants,can cause a series of environmental problems such as haze,acid rain,and photochemical smog.Nowadays,with the improvement of our life,the number of motor vehicles has increased significantly.NO_xemitted from diesel exhaust is the main pollutant source,which is urgent to be controlled immediately.The selective catalytic reduction of NO_x with NH₃（NH₃-SCR）is an effective approach to remove NO_x contaminants,and highly effective catalyst is the key to carry out NH₃-SCR reaction.Currently,V₂O₅-WO₃（MoO₃）/TiO₂catalysts are commercially available in NH₃-SCR technology.However,the narrow active window,the toxicity and volatility of vanadium limit its application in diesel vehicles.Cu-CHA microporous zeolites have been developed and applied by researchers because of their large specific surface area,wide active window,and high hydrothermal stability.Among them,the representatives of Cu-CHA zeolites are Cu-SAPO-34 and Cu-SSZ-13,which have achieved extensive application in the NH₃-SCR technology.Especially the latter one is the best choice to response the national VI NO_x emission standards.In this thesis,Cu-SAPO-34 zeolite was prepared by one-pot method,and then the catalyst was treated at low/high-temperature hydrothermal environment.X-ray powder diffraction（XRD）,scanning electron microscope（SEM）,and H₂ temperature programmed reduction（H₂-TPR）and NH₃-SCR were used to character physicochemical properties and activity.It was found that its structure was not significantly destoryed after different hydrothermal treatment.Moreover,the relative content of Cu²⁺increased after high temperature treatment,raising the NH₃-SCR activity of Cu-SAPO-34.The results confirm that the synthesized Cu-SAPO-34 has strong resistance to low/high-temperature hydrothermal aging.Secondly,Si/Al≈9 SSZ-13 zeolote was synthesized by the crystal transformation method in a 500 m L quick-opened autoclave.USY zeolite was used by the parent zeolite.Its high crystallinity,good morphology and large specific surface area were confirmed by XRD,SEM,BET.At the same time,different ion-exchange methods（straight or traditional ion-exchange）are used to prepare Cu-SSZ-13,and its temperature was optimized.The sam ple obtained by the straight ion-exchange method has the same NH₃-SCR activity and hydrothermal aging resistance as the traditional ion-exchange method.And two ion-exchanged methods negligibly affects the crystallinity and specific surface area of the zeolite.In addition,the optimal ion-exchange temperature for both methods is 80 ^oC.Beyond that,a 5 L quick-opened autoclave was used to synthesize SSZ-13 for expangding product.And the product also has high crystallinity and specific surface area.Moreover,the NH₃-SCR activity of Cu-SSZ-13synthesized by different ion-exchange methods was equivalent.Finally,Cu-SSZ-13 zeolite and silica sol were selected as the catalyst powder and the binder,respectively.Ball milling was used to obtain the stable slurry firstly,and its best time was 9 h.Then,the cordierite ceramic honeycomb was used as the catalyst carrier.Cu-SSZ-13monolithic catalyst was prepared by pull-up coating method.Its shedding rate was tested to find out the optimal ratio of each component,confirming its good binding foece.Finally,the optimal catalyst was tested by NH₃-SCR,confirming its good NH₃-SCR performance.