Preparation,Characterization And Properties Of Copper/Iron-based SAPO-44 Catalysts For The Selective Catalytic Reduction Of NO_x With NH₃

Selective catalytic reduction?SCR?by ammonia is the main technology to remove NOx from motor vehicle exhaust.The catalyst is the key of NH₃-SCR technology.Zeolite based deNOx catalysts are concerned by reseachers due to its excellent high hydrothermal stability and deNOx performances,the chabazite-type Cu/Fe-based SSZ-13 and SAPO-34 zeolite catalysts are widely studied.SAPO-44 is also the chabazite-type zeolite,but it has not been given enough attention.We use different methods to prepare Cu/Fe-based SAPO-44 catalysts and explore their deNOx performances and physical and chemical properties in this thesis.In this thesis,SAPO-44 zeolites were synthesized by using cyclohexylamine,tetraethylenepentamine and cyclohexylamine,N-methyldiethanolamine as templates,respectively.A series of Cu-SAPO-44 were prepared by direct ion exchange method.The optimum catalyst was seletcted by deNOx activity tests.The catalysts were characterized by N2 adsorption-desorption,H2 temperature programmed reduction?H2-TPR?,X-ray absorption fine structure?XAFS?,X-ray powder diffraction?XRD?,scanning electron microscopy?SEM?and ammonia temperature programmed desorption?NH₃-TPD?.Compared to Cu-SAPO-44 prepared by traditional ion exchange method,Cu-SAPO-44 prepared by direct ion exchange method has less content of copper,but their deNOx performances were consistent.We found that Cu-SAPO-44 prepared by direct ion exchange method have higher specific surface area,more acid sites and good redox capacity.Because microporous-mesoporous zeolites have achieved good results in the MTO reaction,we introduced mesopores into SAPO-44 microporous zeolites using the organosilane TPOAC as the mesoporous agent,Cu-SAPO-44 zeolites containing mesoporous were prepared by traditional ion exchange and direct ion exchange method,respectively.Their deNOx performances were studied.The deNOx activity of Cu-SAPO-44 with mesoporous prepared by the traditional ion exchange method is better.But its deNOx activity was lower than the Cu-SAPO-44 microporous molecular sieves prepared by the traditional ion exchange method.Compared to Cu-SAPO-44 microporous molecular sieves,the structure of Cu-SAPO-44 with mesoporous was destroyed more seriously,which results in the decrease of the specific surface area,the number of acid sites,copper content and acid strength.That leads to its lower deNOx activity.A series of Fe-SAPO-44 microporous molecular sieves catalysts were prepared by different methods.The deNOx performances of Fe-SAPO-44 prepared by ion exchange method under a protecting atmosphere of N2 is better.We used various characterization technologies to explore its physical and chemical properties.The Fe-SAPO-44 prepared by ion exchange method under a protecting atmosphere of N2 has a good ability of resistance to hydrothemal aging.