Synthesis of MnNi-SAPO-34 by a one-pot hydrothermal method and its excellent performance for the selective catalytic reduction of NO by NH3

Mn-or/and Ni-modified SAPO-34 molecular sieves (Mn-SAPO-34, Ni-SAPO-34, and MnNi-SAPO-34) were synthesized by a one-pot hydrothermal synthesis method using morpholine as a structure directing agent. XRD, XRF, SEM, TEM-EDX, UV-vis-DRS, NH3-TPD, XPS, NMR, and in situ DRIFTS analyses were performed to study the properties of the samples. The MnNi-SAPO-34 catalyst demonstrated much better NOx conversion (> 95%) and N-2 selectivity (> 98%) for the selective catalytic reduction (SCR) of NOx by NH3 than those of the other catalysts from 320 degrees C to 470 degrees C. Moreover, NOx conversion could still be maintained at about 100% at 380 degrees C even after 80 h over MnNi-SAPO-34. Its excellent activity can be ascribed to the strong interaction between the Mn and Ni species in the framework of MnNi-SAPO-34, leading to the suitable redox ability of MnNi-SAPO-34 by the reaction Ni3+ + Mn3+ <-> Ni2+ + Mn4+. The in situ DRIFTS results suggested that the NH3-SCR reaction was mainly performed by an Eley-Rideal (E-R) reaction pathway at 300 degrees C for the MnNi-SAPO-34 catalyst. Thus, MnNi-SAPO-34 is considered as a promising candidate for controlling NOx emissions at middle temperatures.