MnO_2的晶相结构和表面性质对低温NH_3-SCR反应的影响  

Effects of MnO_2 Crystal Structure and Surface Property on the NH_3-SCR Reaction at Low Temperature

作　　者：戴韵[1] 李俊华[1] 彭悦[1] 唐幸福[2] 

机构地区：[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

出　　处：《物理化学学报》2012年第7期1771-1776,共6页Acta Physico-Chimica Sinica

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

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.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 e-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 （NH^-TPD） suggested that the exposed （110） plane of e-MnO2 had many Mn cations in coordinatively unsaturated environment, while all of the Mn cations on the exposed （001） plane of 5-MnO2 were in coordinatively saturated environment. Thus, e-MnO2 possessed many more Lewis acid sites. Furthermore, e-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 e-MnO2 obtained a higher capability for NH3 and NOx activation than 5-MnO2. The crystal structure and surface properties of e-MnO2 are more suitable to the adsorption of NH3 and activation of NH3 and NOx, which accounts for the higher catalytic activity of the a-MnO2 nanorods.

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. 

分 类 号：O643.32[理学—物理化学]