Manganese-rich MnSAPO-34 molecular sieves as an efficient catalyst for the selective catalytic reduction of NO x with NH 3 : one-pot synthesis, catalytic performance, and characterization

Abstract

Manganese-rich MnSAPO-34 molecular sieves were prepared by one-pot synthesis method for NO_x abatement using the ammonia-selective catalytic reduction (NH₃-SCR) technology and characterized using ICP, BET, XRD, FE-SEM, H₂-TPR, NH₃-TPD, XPS, and DR UV-Vis analyses. The experimental results indicate that the Mn content and chemical state, as well as the surface acidity, of the MnSAPO-34 molecular sieves significantly enhance their DeNO_x efficiency at low temperatures (ca. 200–300 °C). The manganese-rich MnSAPO-34 was synthesized using a combination of triethylamine and diisopropylamine as the structural directing agents and high Mn loading (n(MnO)/n(P₂O₅) = 0.4). The resulting catalyst exhibits the highest activity among all of the samples with a NO_x conversion value of nearly 95% and a N₂ selectivity that is higher than 90% at 220–400 °C. In addition, this catalyst presents higher NO_x conversion than the conventional V₂O₅-WO₃/TiO₂ catalysts and other SAPO-based catalysts below 300 °C. Furthermore, the analytical results indicate that the manganese species in the catalyst are mainly in the form of a framework Mn(IV), which could play a significant role in the NH₃-SCR process as the specific active species. The results suggest that controlling the types and content of the organic amine templates and variations in the surface acidity of the catalysts may significantly enhance the SCR activity at lower temperatures.

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