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

Abstract

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 NO_x conversion (>95%) and N₂ selectivity (>98%) for the selective catalytic reduction (SCR) of NO_x by NH₃ than those of the other catalysts from 320 °C to 470 °C. Moreover, NO_x conversion could still be maintained at about 100% at 380 °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 °C for the MnNi–SAPO-34 catalyst. Thus, MnNi–SAPO-34 is considered as a promising candidate for controlling NO_x emissions at middle temperatures.