Selective catalytic reduction of nitric oxide with propylene over one-step synthesized Cu-SAPO-44 catalysts

Cu-SAPO-44 zeolite catalysts were synthesized by one-step hydrothermal method using cyclohexylamine (CHA) and Cu-amine complex (Cu-TEPA) as co-template. They were used for selective catalytic reduction of nitric oxide with propylene (C₃H₆-SCR) under lean burning condition. These catalysts were characterized by N₂ adsorption-desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis spectroscopy (UV-vis), NH₃ temperature-programmed desorption (NH₃-TPD) and H₂ temperature-programmed reduction (H₂-TPR). Compared with pure SAPO-44, the introduction of Cu-TEPA significantly enhanced the catalytic activity of C₃H₆-SCR. When Cu/Al was 0.25, Cu-SAPO-44 catalyst had the largest specific surface area, abundant acidic sites and moderate isolated Cu²⁺ species, thus it had the best deNO_x performance. With the increase of Cu-TEPA introduction, copper species would aggregate on the surface of the zeolite and form more inactive CuO, thus reducing the denitrification activity. In situ study by DRIFTS indicated that isolated Cu²⁺ could contribute to the adsorption and activation of NO and C₃H₆, thus enhancing in the formation of −NCO, which was a key intermediate of the reaction. The Cu-SAPO-44 catalyst maintained more than 60% NO_x conversion and more than 90% N₂ selectivity in long term test of 50 h, showing appropriate reaction stability.