物理化学学报 >> 2012, Vol. 28 >> Issue (07): 1771-1776.doi: 10.3866/PKU.WHXB201204175

催化和表面科学 上一篇    下一篇

MnO2的晶相结构和表面性质对低温NH3-SCR反应的影响

戴韵1, 李俊华1, 彭悦1, 唐幸福2   

  1. 1. 清华大学环境学院, 环境模拟与污染控制国家重点联合实验室, 北京 100084;
    2. 复旦大学环境科学与工程系, 上海 200433
  • 收稿日期:2012-03-06 修回日期:2012-04-17 发布日期:2012-06-07
  • 通讯作者: 李俊华, 唐幸福 E-mail:lijunhua@tsinghua.edu.cn; tangxf@fudan.edu.cn
  • 基金资助:

    国家自然科学基金(51078203)及国家高技术研究发展计划项目(863) (2010AA065002, 2009AA06Z301)资助

Effects of MnO2 Crystal Structure and Surface Property on the NH3-SCR Reaction at Low Temperature

DAI Yun1, LI Jun-Hua1, PENG Yue1, TANG Xing-Fu2   

  1. 1. State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, P. R. China;
    2. Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, P. R. China
  • Received:2012-03-06 Revised:2012-04-17 Published:2012-06-07
  • Contact: LI Jun-Hua, TANG Xing-Fu E-mail:lijunhua@tsinghua.edu.cn; tangxf@fudan.edu.cn
  • Supported by:

    The project was supported by the National Natural Science Fundation of China (51078203) and National High-Tech Research and Development Program of China (863) (2010AA065002, 2009AA06Z301).

摘要:

采用水热法合成了两种具有相同形貌但是不同物相结构的MnO2纳米棒, 分别为隧道状和层状结构, 考察其低温NH3选择性催化还原NOx (NH3-SCR)的性能. 结果表明MnO2纳米棒的比表面积不是影响活性的主要因素, 催化剂的晶相结构和表面性质对催化活性有很大影响, 隧道状α-MnO2纳米棒的低温NH3-SCR活性明显高于层状δ-MnO2纳米棒. 结构分析和NH3程序升温脱附(NH3-TPD)实验表明, α-MnO2纳米棒的暴露晶面(110)面存在大量的配位不饱和Mn离子, 形成较多的Lewis 酸性位点, 而且α-MnO2较弱的Mn―O键和隧道结构都有利于NH3的吸附; 而δ-MnO2纳米棒的暴露晶面(001)面上的Mn离子已达到配位饱和, 所以其表面Lewis 酸性位点较少. X射线光电子能谱(XPS)和热重(TG)分析表明α-MnO2纳米棒的表面更有利于NH3和NOx的活化. 具有有利于吸附NH3和活化NH3和NOx的表面性质和晶型结构, 是α-MnO2纳米棒活性高的主要原因.

关键词: α-MnO2, δ-MnO2, 低温, NH3-选择性催化还原NOx, 晶相结构, 表面性质

Abstract:

Two manganese oxides with the same nanorod-shaped morphology but different crystal structures, tunnel and layer structures, were synthesized and investigated for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperature. Tunneled α-MnO2 had much higher catalytic activity than layered δ-MnO2 under the same reaction conditions. Experiment results revealed that the surface area was not the main factor to affect the NH3-SCR activities over the MnO2 nanorods and that the activities were structure sensitive. Structure analysis and temperature-programmed desorption experiments of NH3 (NH3-TPD) suggested that the exposed (110) plane of α-MnO2 had many Mn cations in coordinatively unsaturated environment, while all of the Mn cations on the exposed (001) plane of δ-MnO2 were in coordinatively saturated environment. Thus, α-MnO2 possessed many more Lewis acid sites. Furthermore, α-MnO2 has weaker Mn―O bonds and an efficient tunnel structure, which are favorable characteristics for NH3 adsorption. Moreover, X-ray photoelectron spectroscopy (XPS) and thermal gravimetric (TG) analysis indicated that α-MnO2 obtained a higher capability for NH3 and NOx activation than δ-MnO2. The crystal structure and surface properties of α-MnO2 are more suitable to the adsorption of NH3 and activation of NH3 and NOx, which accounts for the higher catalytic activity of the α-MnO2 nanorods.

Key words: α-MnO2, δ-MnO2, Low-temperature, Selective catalytic reduction of NOx with NH3, Crystal structure, Surface property

MSC2000: 

  • O643