Mn-based catalysts supported on γ-Al2O3, TiO2and MCM-41: a comparison for low-temperature NO oxidation with low ratio of O3/NO

Abstract

Mn-Based catalysts supported on γ-Al2O3, TiO2and MCM-41 synthesized by an impregnation method were compared to evaluate their NO catalytic oxidation performance with low ratio O3/NO at low temperature (80-200 °C). Activity tests showed that the participation of O3remarkably promoted the NO oxidation. The catalytic oxidation performance of the three catalysts decreased in the following order: Mn/γ-Al2O3> Mn/TiO2> Mn/MCM-41, indicating that Mn/γ-Al2O3exhibited the best catalytic activity. In addition, there was a clear synergistic effect between Mn/γ-Al2O3and O3, followed by Mn/TiO2and O3. The characterization results of XRD, EDS mapping, BET, H2-TPR, XPS and TG showed that Mn/γ-Al2O3had good manganese dispersion, excellent redox properties, appropriate amounts of coexisting Mn3+and Mn4+and abundant chemically adsorbed oxygen, which ensured its good performance.In situDRIFTS demonstrated the NO adsorption performance on the catalyst surface. As revealed byin situDRIFTS experiments, the chemically adsorbed oxygen, mainly from the decomposition of O3, greatly promoted the NO adsorption and the formation of nitrates. The Mn-based catalysts showed stronger adsorption strength than the corresponding pure supports. Due to the abundant adsorption sites provided by pure γ-Al2O3, under the interaction of Mn and γ-Al2O3, the Mn/γ-Al2O3catalyst exhibited the strongest NO adsorption performance among the three catalysts and produced lots of monodentate nitrates (-O-NO2) and bidentate nitrates (-O2NO), which were the vital intermediate species for NO2formation. Moreover, the NO-TPD studies also demonstrated that Mn/γ-Al2O3showed the best NO desorption performance among the three catalysts. The good NO adsorption and desorption characteristics of Mn/γ-Al2O3improved its high catalytic activity. In addition, the activity test results also suggested that Mn/γ-Al2O3exhibited good SO2tolerance.