Preparation Of New Zeolite Materials And Study On Motor Vehicle Exhaust Gas Purification

Diesel vehicles have attracted much attention because of their low CO2 emissions,high fuel economy and huge power output compared with gasoline vehicles.However,diesel engine can produce more NOx(NO and NO2)emissions,and NOx(NO and NO2)caused by diesel engine combustion in automobile engines has become the main source of air pollution and causes a series of environmental problems,such as photochemical smog and fine particle pollution(haze).Ce and Mn were added to the Cu-SSZ-39 catalyst by ion exchange method,and their activity performance for selective catalytic reduction of NOx with ammonia(NH3-SCR),especially hydrothermal stability(hydrothermal aging at 750,800,850?)were investigated systematically.The catalysts were characterized by XRD,N2 adsorption-desorption,H2-TPR,UV-vis DRS,NH3-TPD and In situ DRIFTS,respectively.The main conclusions are as follows:(1)The SSZ-39 zeolite was synthesized by hydrothermal method and the Cu-SSZ-39,CeCu-SSZ-39 and MnCu-SSZ-39 zeolite catalysts were synthesized by ion-exchange method to investigate the effect of the addition of Ce or Mn on SCR activity of Cu-SSZ-39 catalyst.The results showed that the addition of Ce or Mn significantly improved the activity of Cu-SSZ-39 catalysts,which not only showed a lower T50 but also had a wider active temperature window.This may be attributed to the synergistic effect between Ce or Mn and Cu.Its addition enhances the redox performance and surface acid sites of Cu-SSZ-39,thereby enhancing SCR activity of the Cu-SSZ-39 catalyst.(2)The catalysts were tested under hydrothermal aging conditions of 750,800 and 850?,respectively.To explore the hydrothermal aging ability of the catalyst after adding Ce or Mn.For CeCu-SSZ-39 and MnCu-SSZ-39 catalysts,hydrothermal aging treatment not only has no obvious negative effect,but also has a certain promotion effect on NH3-SCR activity.Especially for the MnCu-SSZ-39 zeolite catalyst,MnCu-SSZ-39 maintains excellent hydrothermal stability even after hydrothermal aging at 850?.From a series of characterization results,it can be seen that the improved hydrothermal stability of the Cu-SSZ-39 catalyst with Ce or Mn addition can be attributed to the formation of more active CuO crystal clusters and higher acid strength in the inner channel.And during hydrothermal aging,the addition of Ce or Mn not only inhibited the aggregation of Cu oxides,but more Cu2+ion species were transferred to ion exchange sites,which may be the reason for the excellent hydrothermal stability of the Cu-SSZ-39 catalyst after the addition of Ce or Mn.(3)The In situ DRIFTS reflectance was used to analyze SCR mechanism on fresh and aged Cu-SSZ-39,CeCu-SSZ-39 and MnCu-SSZ-39 catalysts.The NH3-SCR reaction on Cu-SSZ-39 and CeCu-SSZ-39 samples follows the"Langmuir-Hinshelwood"(L-H)mechanism.Whereas on MnCu-SSZ-39 catalyst,it follows both "L-H" and "Eley-Rideal"(E-R)mechanism,which may also be another reason for its good activity and hydrothermal stability.After hydrothermal aging treatment,the NH3-SCR reaction on the A-MnCu-SSZ-39 sample followed the"L-H" and "E-R" mechanisms,and the "Fast SCR" reaction also occurred simultaneously.Therefore,Cu-SSZ-39 catalyst after Mn addition shows excellent activity and super hydrothermal stability.Even after hydrothermal aging at 850?,it can meet the complex operating conditions and durability requirements of diesel engines,showing a broad application prospect.