物理化学学报 >> 2016, Vol. 32 >> Issue (6): 1501-1510.doi: 10.3866/PKU.WHXB201603171

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二氧化锰在低温NH3-SCR催化反应上的形貌效应

孙梦婷1,黄碧纯1,2,*(),马杰文1,李时卉1,董立夫1   

  1. 1 华南理工大学环境与能源学院，广州510006
    2 华南理工大学，工业聚集区污染控制与生态修复教育部重点实验室，广州510006
  • 收稿日期:2015-12-23 发布日期:2016-06-03
  • 通讯作者: 黄碧纯 E-mail:cebhuang@scut.edu.cn
  • 基金资助:
    国家自然科学基金(51478191);广东省省级科技计划项目(2014A020216003)

Morphological Effects of Manganese Dioxide on Catalytic Reactions for Low-Temperature NH3-SCR

Meng-Ting SUN1,Bi-Chun HUANG1,2,*(),Jie-Wen MA1,Shi-Hui LI1,Li-Fu DONG1   

  1. 1 College of Environment and Energy, South China University of Technology, Guangzhou 510006, P. R. China
    2 Key Laboratory of the Ministry of Education for Pollution Control and Ecosystem Restoration in Industry Clusters,South China University of Technology, Guangzhou 510006, P. R. China
  • Received:2015-12-23 Published:2016-06-03
  • Contact: Bi-Chun HUANG E-mail:cebhuang@scut.edu.cn
  • Supported by:
    The project was supported by the National Natural Science Foundation of China(51478191);Guangdong Provincial Science and Technology Project, China(2014A020216003)

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摘要：

利用水热法制备了三种不同形貌的MnO2催化剂，分别为α-MnO2纳米棒，γ-MnO2纳米片和δ-MnO2纳米薄膜组装的微球，考察了纳米材料的形貌结构对催化剂低温选择性催化还原(SCR)反应性能的影响，并利用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、N2吸附-脱附、H2程序升温还原(H2-TPR)、NH3程序升温脱附(NH3-TPD)、X射线光电子能谱(XPS)以及拉曼(Raman)光谱等表征手段对催化剂的结构进行了分析。结果表明，在50-250 ℃的温度范围内，γ-MnO2纳米片表现出最优的SCR催化性能，不仅NOx转化率最高而且N2选择性也最好。表征结果表明，比表面积并不是影响MnO2催化性能的主导因素，纳米材料的晶型结构与表面暴露的活性晶面共同决定着催化剂的SCR性能。γ-MnO2纳米片表面暴露的(131)晶面上不仅存在着大量的配位不饱和Mn离子，从而形成了较多的强酸性位点；而且还存在着较多的活性氧物种。这些活性位点可以使得NH3和NOx的活化过程在较低温度下进行。高浓度的流动性氧以及高价态的Mn3+和Mn4+也使得催化剂的氧化还原反应更易发生。

关键词: 选择性催化还原, 氮氧化物, MnO2纳米材料, 水热合成, 形貌效应

Abstract:

α-MnO2 nanorods,γ-MnO2 nanosheets,and δ-MnO2 nanofilm-assembled microspheres wereprepared using a hydrothermal method and evaluated as catalysts for the selective catalytic reduction(SCR)of nitrogen oxides(NOx).They were also structurally characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),N2 adsorption- desorption,temperatureprogrammedreduction with hydrogen(H2-TPR),temperature-programmed desorption of ammonia(NH3-TPD),X-ray photoelectron spectroscopy(XPS),and Raman spectroscopy.The γ-MnO2 nanosheets performed thebest for the reduction of NOx and selectivity of N2,while the α-MnO2 nanorods performed the worst.Structuralanalysis indicated that the main factor determining the catalytic activities of the nanomaterials was not thespecific surface area but the crystal structure and the exposed active crystals.The γ-MnO2 nanosheets performedbest because their exposed(131)planes contained multiple Mn cations in coordinatively unsaturatedenvironments,which formed numerous strongly acidic sites.They also benefited from active oxygen species.The active sites allowed the activation of NH3 and NOx at lower temperatures.Moreover,high concentrationsof liquid oxygen and Mn cations at high oxidation states facilitated the redox reactions.

Key words: Selective catalytic reduction, Nitrogen oxide, MnO2 nanomaterial, Hydrothermal synthesis, Morphology effect