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首页> 外文期刊>Journal of porous materials >Characterization and temperature evolution of iron-containing species in HZSM-5 zeolite prepared from different iron sources
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Characterization and temperature evolution of iron-containing species in HZSM-5 zeolite prepared from different iron sources

机译：用不同铁源制备的HZSM-5沸石中含铁物种的表征及温度演变

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Iron-containing HZSM-5 zeolites are materials with important industrial applications as catalysts. Their characterization is difficult due to the various possible Fe-containing species which can exist in the pores of HZSM-5 zeolites and their dependence on the preparation technique. Three Fe-HZSM-5 samples were prepared by ion-exchange technique using different iron precursors: containing only Fe2+ or Fe3+ ions, and containing equimolar mixture of Fe2+ and Fe3+ ions. The samples were characterized by various experimental techniques (XRD, FTIR, UV-Vis spectroscopy and XANES/EXAFS) in order to clarify the type of the Fe-containing species existing in the samples. Periodic density functional calculations were also performed to help in elucidation of the obtained structural information with the EXAFS data and in clarification of the relative stability of the various Fe-containing species in the pores of the HZSM-5 zeolites. In the samples prepared with only Fe2+ or Fe3+ ions dominate isolated iron species but binuclear FeOFe2+ species and small iron oxide clusters are also present. In the third sample, prepared from a precursor containing iron ions in both oxidation states, most of the iron is included in the iron oxide clusters or small nanoparticles. The time-resolved XAS for the sample containing equimolar Fe2+ and Fe3+ ions revealed existence of two types of dominant iron oxide species-small oligonuclear clusters in the temperature region 100-300 degrees C and larger more oxidized moieties (nanoparticles) after heating the sample up to 400 and 500 degrees C.
机译：含铁HZSM-5沸石是具有重要工业应用作为催化剂的材料。由于HzSM-5沸石的孔中可以存在的各种可能的Fe含量物质及其对制备技术的依赖性，它们的表征是困难的。使用不同铁前体的离子交换技术制备三种Fe-HzSM-5样品：仅含有Fe2 +或Fe3 +离子，并含有Fe2 +和Fe 3 +离子的等摩尔混合物。样品的特征在于各种实验技术（XRD，FTIR，UV-Vis光谱和Xanes / Exafs），以澄清样品中存在的含Fe物种的类型。还进行周期密度官能计算以帮助阐明所获得的结构信息与EXAFS数据，并在HZSM-5沸石的孔中阐明各种含Fe物种的相对稳定性。在仅用Fe2 +或Fe3 +离子中制备的样品中，存在孤立的铁物质，但也存在双核FeoFe2 +物种和小氧化铁簇。在第三个样品中，由氧化态的含铁离子的前体制备，大部分铁包括在氧化铁簇或小纳米颗粒中。含有Equimolar Fe2 +和Fe3 +离子的样品的时间分辨XA显示在加热样品后，在温度区域100-300℃和更大的氧化部分（纳米粒子）中存在两种类型的显性氧化铁物质 - 小寡清核簇的存在到400和500摄氏度。

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