Preparation Of New Transition Metal Zeolite Materials And Study On Diesel Vehicle Exhaust Gas Purification

Diesel vehicles have become the choice of more and more people because of their sufficient power,good fuel economy and low emissions of CO₂,CO and HC.However,the content of NO_x in diesel vehicle exhaust is high,which is the main mobile emission source of nitrogen oxide（NO_x）in the atmosphere.Lead to a series of environmental problems,such as acid rain,photochemical smog,ozone layer destruction and so on.The health of our is being endangered by exhaust fumes.Therefore,it is very important to purify NO_x from diesel exhaust.It is used to NH₃-SCR method to purify diesel vehicle exhaust.Cu-SAPO-34and Fe-MOR were synthesized by ion exchange method.And it’s synthesized Cu-SAPO-34@Fe-MOR Core shell zeolite catalyst.Their activity performance for selective catalytic reduction of NO_x with ammonia（NH₃-SCR）,especially hydrothermal stability（hydrothermal aging at 750°C,10%H₂O）were investigated systematically.The catalysts were characterized by XRD,SEM,TEM,N₂ adsorption-desorption,H₂-TPR,UV-vis DRS,NH₃-TPD and In situ DRIFTS,respectively.The main conclusions are as follows:（1）Cu-SAPO-34 and Fe-MOR were prepared by ion exchange method and Cu-SAPO-34@Fe-MOR core-shell zeolite were synthesized under the condition that the concentration of silica sol was 10%and m _Cu-SAPO-34/m _Fe-MORwas 1:2.The results showed that the SCR performance of Cu-SAPO-34@Fe-MOR is improved,the temperature window is broadened and the activity at high temperature is increased.This may be attributed to the addition of Fe-MOR,the increase of isolated iron ions and the enhancement of the synergistic effect of copper and iron ions.NO_x is easy to desorb on Cu-SAPO-34@Fe-MOR.Thereby enhancing SCR activity of the Cu-SAPO-34@Fe-MOR catalyst.（2）In order to further investigate the application prospect of Cu-SAPO-34@Fe-MOR core-shell catalyst in diesel vehicle exhaust gas purification.The catalysts were tested under hydrothermal aging conditions of 750℃and 10%H₂O for 12 hours,and their hydrothermal stability was investigated.The results showed that the SCR activity of Cu-SAPO-34@Fe-MOR-750 was significantly higher than that of Cu-SAPO-34-750,and the decrease of SCR performance was the smallest compared with its fresh samples.Thus it can be seen that the preparation of core-shell catalyst by compounding Fe-MOR with good hydrothermal stability on Cu-SAPO-34 will improve the hydrothermal stability of Cu-SAPO-34.By means of H₂-TPR,NH₃-TPD and UV-vis DRS,it was found that the micropore structure of the catalyst was not destroyed after hydrothermal aging,and the decrease of specific surface area and pore volume was the smallest.And compared with other aging samples,there are more isolated copper and iron ions,the most active species remain and the least acid loss.The number of NO_x species and nitrate species adsorbed on the surface of the catalyst increased,which was beneficial to the SCR reaction.These may be the reasons for the good hydrothermal stability of Cu-SAPO-34@Fe-MOR.Therefore,Cu-SAPO-34@Fe-MOR not only has good activity,but also has high hydrothermal stability and low cost,so it has a good application prospect in diesel vehicle exhaust gas purification research.（3）The intermediate species and reaction process were characterized by In situ DRIFTS,and the catalytic process and reaction mechanism of core-shell catalyst Cu-SAPO-34@Fe-MOR were revealed.The results showed that the main NH₃ species adsorbed by Cu-SAPO-34@Fe-MOR were NH₄⁺species and NH₃ species at Br?nsted acid site and NH₃ species at Lewis acid site.The main NO_x species adsorbed are monodentate nitrate,chelated nitrite and nitrite species.The SCR reaction on Cu-SAPO-34 and Cu-SAPO-34@Fe-MOR and their aging samples follows the"L-H"mechanism.