MOF-74 as an Efficient Catalyst for the Low-Temperature Selective Catalytic Reduction of NO_x with NH₃

In this work, Mn-MOF-74 with hollow spherical structure and Co-MOF-74 with petal-like shape have been prepared successfully via the hydrothermal method. The catalysts were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry-mass spectrum analysis (TG-MS), N₂ adsorption/desorption, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). It is found that MOF-74(Mn, Co) exhibits the capability for selective catalytic reduction (SCR) of NO_x at low temperatures. Both experimental (temperature-programmed desorption, TPD) and computational methods have shown that Co-MOF-74 and Mn-MOF-74 owned high adsorption and activation abilities for NO and NH₃. The catalytic activities of Mn-MOF-74 and Co-MOF-74 for low-temperature denitrification (deNO_x) in the presence of NH₃ were 99% at 220 °C and 70% at 210 °C, respectively. It is found that the coordinatively unsaturated metal sites (CUSs) in M-MOF-74 (M = Mn and Co) played important roles in SCR reaction. M-MOF-74 (M = Mn and Co), especially Mn-MOF-74, showed excellent catalytic performance for low-temperature SCR. In addition, in the reaction process, NO conversion on Mn-MOF-74 decreased with the introduction of H₂O and SO₂ and almost recovered when gas was cut off. However, for Co-MOF-74, SO₂ almost has no effect on the catalytic activity. This work showed that MOF-74 could be used prospectively as deNO_x catalyst.