Sm-doped manganese-based Zr–Fe polymeric pillared interlayered montmorillonite for low temperature selective catalytic reduction of NOx by NH3 in metallurgical sintering flue gas

Abstract

In this work, Sm-doped manganese supported Zr–Fe polymeric pillared interlayered montmorillonites (Mn/ZrFe-PILMs) were prepared for the low-temperature selective catalytic reduction (SCR) of NO_x with NH₃ in metallurgical sintering flue gas. These pillared interlayered montmorillonite catalysts were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, nitrogen adsorption–desorption isotherm, ammonia temperature-programmed desorption, and hydrogen temperature-programmed reduction to study the influence of Sm doping on the SCR performance. The ZrFe-PILMs with a Mn/Sm molar ratio of 18 : 2 showed the excellent SCR activity among these catalysts, where a 95.5% NO_x conversion ratio at 200 °C at a space velocity of 20 000 h⁻¹ was obtained. Samarium oxide and manganese oxides were highly dispersed on the ZrFe-PILMs with different Mn/Sm molar ratios by the XRD results and SEM-EDS results. Meanwhile, the Mn–Sm/ZrFe-PILM (18 : 2) had the lowest temperature hydrogen reduction peak by H₂-TPR results, which indicated that it had the lowest active bond energy on its surface. And the NH₃-TPD results expressed that the Mn–Sm/ZrFe-PILM (18 : 2) had the most acidic sites, especially the weakly acidic sites. Therefore, it was found that the introduction of a small amount of Sm (Mn : Sm = 18 : 2) to Mn/ZrFe-PILM can significantly improve catalytic activity by the increased active oxygen component and the surface acidity.