Preparation And Properties Of Cu-SAPO-44 Catalyst For The Selective Catalytic Reduction Of NO_x With NH₃

Selective Catalytic Reduction of NOx by ammonia(NH3-SCR) is an effective technology for the abatement of NOx discharged from exhaust gases of stationary and mobile source. In the batement of NOx from the diesel engines, WO3 or MoO3 promoted V2O5/TiO2 catalysts have been replaced gradually by zeolite based deNOx catalysts due to its wide activity temperature window and high hydrothermal stability. Especially, Cu-exchanged small pore CHA zeolites, such as Cu-SSZ-13 and Cu-SAPO-34, have been drawn much attention in the application of zeolites materials for the elimination of NOx. The CHA structure has also been reported as silicoaluminophos-phate form in SAPO-44. So this paper is foused on the synthesis method of the SAPO-44 zeolite by improved synthetic routes and application of complex organic structure directing agents. We have successfully synthetized SAPO-44 and Cu-SAPO-44 zeolites. Furthermore, the catalytic property of the Cu-SAPO-44 zeolite catalysts and the existence forms of the Cu species were investigated.In this paper, we proposed a new synthesis method for SAPO-44. To do this, a rationalized use of cooperative OSDAs is proposed, consisting of the combination of triethylenetetramine(TEPA) with N, N, N’, N’-Tetramethyl-1,6-hexanediamine(TMHD) to direct the crystallization towards SAPO-44 and Cu-SAPO-44. We have seletcted the optimal catalyst from different samples using de NOx tests. A series of Cu-SAPO-44 zeolites were characterized by X-ray powder diffraction(XRD), N2 adsorption-desorption, inductively coupled plasma atomic emission spectrometry(ICP-AES), scanning electron microscope(SEM), high angle annular dark-field imaging scanning transmission electron microscope(HAADF-STEM), X-ray absorption fine structure(XAFS) and temperature programmed reduction(TPR). The results show that the catalytic active sites are highly dispersive CuO and Cu2+species.For the purpose of cutting down the synthetic cost of the Cu-SAPO-44 zeolites, the cheaper cyclohexylamine(CHA) instead of TMHD, combining with TEPA was successfully used to synthesize Cu-SAPO-44 with different copper content. The best catalyst was obtained by suitable post-treatment ways, which exhibites optimal deNOx property.