Mn-based catalysts supported on γ-Al2O3, TiO2 and MCM-41: a comparison for low-temperature NO oxidation with low ratio of O3/NO |
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| Authors: | Lijun Liu Boxiong Shen Meng Si Peng Yuan Fengju Lu Hongpei Gao Yan Yao Cai Liang Hongjie Xu |
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| Affiliation: | School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin China.; School of Chemical Engineering, Hebei University of Technology, Tianjin China ; China Huaneng Group, Clean Energy Technology Research Institute Co. Ltd, Beijing China ; Suzhou TPRI Energy & Environment Technology Co. Ltd, Suzhou China ; Chengdu Dongfang KWH Environmental Protection Catalysts Co. Ltd, Chengdu China ; Xi''an Thermal Engineering Institute, Xi''an China |
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| Abstract: | Mn-Based catalysts supported on γ-Al2O3, TiO2 and 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 O3 remarkably 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-Al2O3 exhibited the best catalytic activity. In addition, there was a clear synergistic effect between Mn/γ-Al2O3 and O3, followed by Mn/TiO2 and O3. The characterization results of XRD, EDS mapping, BET, H2-TPR, XPS and TG showed that Mn/γ-Al2O3 had good manganese dispersion, excellent redox properties, appropriate amounts of coexisting Mn3+ and Mn4+ and abundant chemically adsorbed oxygen, which ensured its good performance. In situ DRIFTS demonstrated the NO adsorption performance on the catalyst surface. As revealed by in situ DRIFTS 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-Al2O3 catalyst 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 NO2 formation. Moreover, the NO–TPD studies also demonstrated that Mn/γ-Al2O3 showed the best NO desorption performance among the three catalysts. The good NO adsorption and desorption characteristics of Mn/γ-Al2O3 improved its high catalytic activity. In addition, the activity test results also suggested that Mn/γ-Al2O3 exhibited good SO2 tolerance.The Mn/γ-Al2O3 catalyst exhibited excellent performance for NO conversion in the presence of a low ratio of O3/NO, which was due to the coexistence of Mn3+ and Mn4+ and abundant chemically adsorbed oxygen. |
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