The determination of the activities of different iron species in Fe-ZSM-5 for SCR of NO by NH3
The determination of the activities of different iron species in Fe-ZSM-5 for SCR of NO by NH3
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DOI：
10.1016/j.apcatb.2010.01.013
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发表时间：
2010-04-06
影响因子：
22.1
通讯作者：
Althoff, Roderik
中科院分区：
文献类型：
--
作者：
Brandenberger, Sandro;Kroecher, Oliver;Althoff, Roderik
Fe-ZSM-5 中不同铁物种对 NH3 选择性催化还原 (SCR) NO 的活性根据其周转频率（TOF 值）确定。不同物种的相对浓度与其测量的 NOx 还原效率和 NH3 氧化活性相关。我们的结果表明，NH3 对 NO 的 SCR 催化是由具有不同活化能的不同活性位点催化的。在低于 300 摄氏度的温度下，观察到 SCR 活性主要由单体铁位点引起：然而，在 T > 300 摄氏度、T >= 400 摄氏度和 T >= 500 摄氏度时，氧化铁颗粒最外层中二聚铁物质、低聚铁物质（例如三聚和四聚铁物质）和部分不配位铁位点的贡献分别变得重要。单体和二聚位点的活化能分别约为 36 kJ/mol 和 77 kJ/mol。由于其高活化能，二聚体位点在较高温度下对整体 SCR 活性的贡献比单体位点更大。聚集位点不仅有助于 SCR 活性，而且在 T >= 350 摄氏度时引起 NH3 的非选择性氧化，而二聚体在 T = 500 摄氏度时控制 NH3 氧化活性。二聚体的 TOF 值在 500 摄氏度时估计为 70 +/- 13 s(-1)。发现单体位点在高达 500 摄氏度时对 NH3 氧化完全不活跃。 (C) 2010 Elsevier B.V. 保留所有权利。
The activities of different iron species in Fe-ZSM-5 for the selective catalytic reduction (SCR) of NO by NH3 were determined in terms of their turnover frequencies (TOF values). The relative concentrations of different species were correlated with their measured NOx reduction efficiencies and NH3 oxidation activities. Our results suggest that the SCR of NO by NH3 is catalyzed by different active sites with different activation energies. At temperatures below 300 degrees C, the SCR activity was observed to be primarily caused by monomeric iron sites: however, at T > 300 degrees C, T >= 400 degrees C and T >= 500 degrees C, the contribution of dimeric iron species, oligomeric species (e.g., trimeric and tetrameric iron species) and partially uncoordinated iron sites in the outmost layer of iron oxide particles, respectively, become important. The activation energies for monomeric and dimeric sites were evaluated to be about 36 kJ/mol and 77 kJ/mol, respectively. Due to their high activation energies, dimeric sites contributed more to the overall SCR activity at higher temperatures than did monomeric sites. The clustered sites not only contributed to the SCR activity but also caused nonselective oxidation of NH3 at T >= 350 degrees C, whereas the dimeric species governed the NH3 oxidation activity up to T = 500 degrees C. The TOF values for dimeric species were estimated to be 70 +/- 13 s(-1) at 500 degrees C. Monomeric sites were found to be completely inactive for NH3 oxidation up to 500 degrees C. (C) 2010 Elsevier B.V. All rights reserved.