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首页> 外文期刊>Coordination chemistry reviews >Structure of aluminum, iron, and other heteroatoms in zeolites by X-ray absorption spectroscopy
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Structure of aluminum, iron, and other heteroatoms in zeolites by X-ray absorption spectroscopy

机译：X射线吸收光谱法研究沸石中铝，铁和其他杂原子的结构

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摘要

Heteroatoms in zeolites provide them their catalytic activity. The silicon atom is always tetrahedrally coordinated and its valence Ⅳ, those of the heteroatoms much more varied. This is further complicated by the easy removal of heteroatoms out of the zeolite framework forming extra-framework phases. The change in coordination and removal of the framework atoms is often paralleled with enhanced catalytic performance and thus the precise characterization of heteroatoms in zeolites, as a function of synthesis and post-synthesis treatments, is topic of much research. In this review we summarize structural characterization of various heteroatoms using X-ray absorption spectroscopy. This method is in particular suitable, because it is element-specific, can be used to determine structure of amorphous samples, and can be applied under pretreatment and catalytic conditions. Aluminum shows a rich variation in coordination and, depending on the conditions, such as temperature and, notably, water content, zeolitic aluminum can be three, four, five and six-coordinate. The Bronsted acid site is associated with a strongly distorted tetrahedral coordination of the framework aluminum. During activation and along catalytic reactions, there is a large variation in the distortion of the local environment of aluminum, and the flexibility of the zeolite framework to accommodate such structural differences is essential to guarantee a long life time of the material as working catalyst. Iron in the zeolite framework is easily removed. The extra-framework iron species are extensively characterized, however, no consensus about their structure has been reached. Framework iron is Fe~(3+), extra-framework iron mostly Fe~(2+). The coordination of other tri- and tetravalent heteroatoms, such as gallium, boron, titanium, germanium, and tin are less investigated. It is however obvious that their structure is a function of the conditions the zeolite is exposed to. Like aluminum, the titanium atom easily switches coordination in a reversible way. All hetero-atoms often form extra-framework species. This review identifies the importance of changes in local structure of heteroatoms and the easy removal of these hetero-atoms from the framework. Often it is the extra-framework species that is responsible for catalytic activity.
机译：沸石中的杂原子为其提供了催化活性。硅原子始终是四面体配位的，其价态Ⅳ（杂原子的价态得多）。由于容易从沸石骨架中除去杂原子，从而形成骨架外相，使情况进一步复杂化。骨架原子的配位和去除的变化通常与增强的催化性能平行，因此，沸石中杂原子的精确表征（取决于合成和后合成处理）是许多研究的主题。在这篇综述中，我们使用X射线吸收光谱法总结了各种杂原子的结构表征。该方法特别适合，因为它是特定于元素的，可用于确定无定形样品的结构，并可在预处理和催化条件下应用。铝显示出丰富的配位变化，并且取决于条件，例如温度，尤其是水含量，沸石铝可以是三，四，五和六坐标。布朗斯台德酸位点与骨架铝的强烈扭曲的四面体配位有关。在活化过程中以及沿着催化反应，铝局部环境的形变有很大的变化，而沸石骨架适应这种结构差异的柔韧性对于保证材料作为工作催化剂的长寿命至关重要。沸石骨架中的铁很容易去除。骨架外的铁物种具有广泛的特征，但尚未就其结构达成共识。骨架铁为Fe〜（3+），骨架外铁多为Fe〜（2+）。其他三价和四价杂原子（如镓，硼，钛，锗和锡）的配位研究较少。但是很明显，它们的结构是沸石暴露条件的函数。像铝一样，钛原子很容易以可逆的方式切换配位。所有杂原子通常形成骨架外的物种。这篇综述指出了改变杂原子局部结构的重要性以及从框架中轻松去除这些杂原子的重要性。通常是骨架外的物种负责催化活性。

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  • 来源
    《Coordination chemistry reviews》 |2014年第10期|275-290|共16页
  • 作者

    Jeroen A. van Bokhoven; Carlo Lamberti;

  • 作者单位

    Institute for Chemical and Bioengineering, ETH Zuerich, CH-8093 Zurich, Switzerland,Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland;

    Department of Chemistry and NIS, CrisDi Interdepartmental Centers, Universita di Torino, Via P. Giuria 7, I-10125 Torino, Italy,INSTM Reference Center, University of Turin, Via P. Giuria 7, I-10125 Torino, Italy,Southern Federal University, Zorge Street 5, 344090 Rostov-on-Don, Russia Torino, Italy;

  • 收录信息 美国《科学引文索引》(SCI);美国《生物学医学文摘》(MEDLINE);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    EXAFS; XANES; Aluminum coordination; Zeolite; Heteroatom; In situ;

    机译：EXAFS;XANES;铝配合;沸石;杂原子;原位;

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