Chromium, iron or zirconium oligomer cations pillared interlayered montmorillonite carrier supported MnO_x for low-temperature selective catalytic reduction of NO_x by NH₃ in metallurgical sintering flue gas

ABSTRACT

The chromium, iron or zirconium oligomer cations pillared interlayered montmorillonite supported 10 wt% MnO_x were synthesized and studied for the flue gas NO_x removal in metallurgical sintering process. The physicochemical properties of these catalysts were detected by some characterization methods, such as XRD, N₂ adsorption–desorption, SEM, H₂-TPR, and NH₃-TPD. The Mn/Zr-PILM catalyst had the highest NO_x conversion with 91.8% at 200°C. And the Mn/Fe-PILM catalyst had the highest NO_x conversion between 140°C and 160°C. This is because zirconium or iron pillared montmorillonite increases the specific surface area and acidic sites of catalyst, which provided more adsorption sites and activation sites for NO and NH₃, thus promoting low-temperature catalytic activity. The XRD results expressed that the pillared elements successfully pillared into Na-montmorillonite and the manganese active components had good dispersibility on the surface of catalyst. The N₂ adsorption–desorption isotherm indicated that the metal pillared carrier had fractured mesoporous structure and the specific surface area was increased. The Mn/Zr-PILM and Mn/Fe-PILM catalyst had abundant acidity with 61.56 μmol/g and 57.71 μmol/g, respectively. The large amount of acid sites favored the adsorption of ammonia in the Langmuir–Hinshelwood or Eley–Rideal mechanisms in the low-temperature NH₃-SCR process. The Mn/Fe-PILM catalyst had the best N₂ selectivity and Mn/Cr-PILM has poor N₂ selectivity. This was due to that iron element restrains the side reaction for N₂O production and chromium promoted the N₂O production by strong oxidation.

KEYWORDS:

• Pillared interlayered montmorillonite
• NH₃-SCR
• low temperature
• oxygen excessive
• metallurgical sintering flue gas

Additional information

Funding

This research was supported by the Major State Research Development Program of China (2017YFB0603603) and National Natural Science Foundation of China (51576035).