Chinese Journal of Catalysis ›› 2013, Vol. 34 ›› Issue (5): 876-888.DOI: 10.1016/S1872-2067(12)60555-5

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Catalytic performance of different types of iron zeolites in N2O decomposition

WANG Junyinga,b, XIA Haiana, JU Xiaohuaa, FAN Fengtaoa, FENG Zhaochia, LI Cana   

  1. a State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China;
    b Graduate University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2012-12-26 Revised:2013-05-20 Online:2013-05-06 Published:2013-05-06
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21173213) and the National Basic Research Program of China (973 Program, 2009CB623507).

Abstract:

A series of Fe/zeolites (ZSM-35, ZSM-5, beta, and mordenite) samples with Fe/Al molar ratios of 0.33 were prepared using a solid-state ion-exchange method. A combination of ultraviolet-visible diffuse reflectance, in-situ Fourier-transform infrared, and in-situ visible Raman spectroscopic techniques, with a transient response method, was used to investigate the influence of the zeolite framework on the catalytic properties of the Fe/zeolites in N2O decomposition. The results show that the catalytic activity of the Fe/zeolites-HT (HT denotes high-temperature treatment) samples is in the order Fe/ZSM-35-HT > Fe/beta-HT > Fe/ZSM-5-HT > Fe/mordenite-HT. There is a linear relationship between the rate of N2O decomposition and the concentration of binuclear iron sites. This indicates that binuclear iron sites are the active sites for N2O decomposition. A correlation between the formation of binuclear iron sites and Fe ion distribution among the cationic sites is proposed. Two Fe(II) cations located in two adjacent six-membered rings in a 10-membered ring channel (α sites) or in two neighboring six-membered rings in an eight-membered ring channel (β sites) of Fe/ZSM-35 are favorable for the formation of active binuclear iron sites. Similar structure can also be formed in two adjacent six-membered rings in polymorphs A and B of beta zeolite or in the six-membered rings at the intersection of the straight and sinusoidal channels of the ZSM-5 framework. For the Fe/mordenite-HT sample, most of the iron species are present as isolated iron cations, so it has the lowest activity in N2O decomposition.

Key words: Iron, Zeolite, Nitrous oxide decomposition, Raman spectroscopy