Acta Phys. -Chim. Sin. ›› 2012, Vol. 28 ›› Issue (07): 1771-1776.doi: 10.3866/PKU.WHXB201204175

• CATALYSIS AND SURFACE SCIENCE • Previous Articles     Next Articles

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).

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