Effect of Copper Precursors on the Activity and Hydrothermal Stability of CuII-SSZ-13 NH3-SCR Catalysts

A series of Cu-II-SSZ-13 catalysts are prepared by in-situ hydrothermal method using different copper precursors (Cu-II(NO3)(2), (CuSO4)-S-II, (CuCl2)-Cl-II) for selective catalytic reduction of NO by NH3 in a simulated diesel vehicle exhaust. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), N-2 adsorption-desorption, hydrogen-temperature-programmed reduction (H-2-TPR), ammonia temperature-programmed desorption (NH3-TPD), and( 27)Al and Si-29 solid state Nuclear Magnetic Resonance (NMR). The Cu-II-SSZ-13 catalyst prepared by Cu-II(NO3)(2) shows excellent catalytic activity and hydrothermal stability. The NO conversion of Cu-II-SSZ-13 catalyst prepared by Cu-II(NO3)(2) reaches 90% at 180 degrees C and can remain above 90% at a wide temperature range of 180-700 degrees C. After aging treatment at 800 degrees C for 20 h, the Cu-II-SSZ-13 catalyst prepared by Cu-II(NO3)(2) still exhibits above 90% NO conversion under a temperature range of 240-600 degrees C. The distribution of Cu species and the Si/Al ratios in the framework of the synthesized Cu-II-SSZ-13 catalysts, which determine the catalytic activity and the hydrothermal stability of the catalysts, are dependent on the adsorption capacity of anions to the cation during the crystallization process due to the so called Hofmeister anion effects, the NO3- ion has the strongest adsorption capacity among the three kinds of anions (NO3 , Cl , and SO42-), followed by Cl - and SO42- ions. Therefore, the Cu-II-SSZ-13 catalyst prepared by Cu-II(NO3)(2) possess the best catalytic ability and hydrothermal stability.