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Beyond tetrahedral coordination in zeolite-type materials - A computational approach

超越沸石型材料中的四面体配位——一种计算方法

基本信息

批准号：
389577027
负责人：
Dr. Michael Fischer
金额：
--
依托单位：
Fachgebiet Kristallographie und Geomaterialforschung
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2021-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/389577027?language=en
关键词：
Beyond tetrahedral coordination zeolite type

项目摘要

Zeolites are a class of crystalline inorganic materials consisting of a three-dimensional framework of corner-sharing tetrahedra. By virtue of their intrinsic porosity, zeolites and related materials with zeolite-type topologies (zeotypes) find use in various large-scale applications, e.g. in gas and liquid separation, catalysis, and ion exchange. Ideal zeolites correspond to a perfect framework of tetrahedrally coordinated atoms (T atoms) linked by oxygen atoms. However, there are many examples of actual zeolite structures where some T atoms have a coordination number (CN) that is larger than 4 because additional non-bridging species are bonded to these sites.The present project explores such zeolite-type materials with 'higher-coordinated' T atoms by means of electronic structure calculations in the framework of dispersion-corrected density-functional theory (DFT). The focus will be on two groups of materials, namely (1) fluoride-containing all-silica zeolites and (2) hydrated aluminophosphates (AlPOs). In the former group, fluoride anions are covalently bonded to framework Si atoms, forming trigonal-bipyramidal SiO4F- units. In hydrated AlPOs, the coordination of water to framework Al atoms leads to the formation of five- or six-coordinated aluminium. While the existence of higher-coordinated T atoms is well-known for both groups, it remains largely unclear why their formation occurs preferentially at certain positions. To address this, DFT calculations will be employed to elucidate the crystal-chemical factors that determine which T atoms in a structure are most susceptible to assume a coordination number beyond 4. These structural investigations will be complemented by a DFT-based prediction of the vibrational properties to gain further insights into the host-guest interactions. Furthermore, these calculations will serve to identify fingerprint modes that indicate the presence of higher-coordinated T atoms in the vibrational spectra. For fluoride-containing all-silica zeolites, additional Molecular Dynamics calculations will be used to study fluoride anion disorder. Finally, the bonding and dynamics of fluoride in germanium-containing zeotypes will be investigated, as there are some conflicting observations regarding the existence of GeO4F- units in these systems.It is the primary aim of the project to further the understanding of zeolite-type systems with higher-coordinated T atoms on a fundamental level. Nevertheless, it can be anticipated that the findings will also have a certain relevance to applications. For example, new insights into the structure-directing properties of fluoride anions may aid the rational development of new synthesis routes, and a better atomic-level understanding of the framework-water interaction in hydrated AlPOs can help to explain the different degree of water stability of these materials, which is a crucial property for various applications.

沸石是一类由共角四面体的三维骨架组成的晶体无机材料。由于其固有孔隙率，具有沸石型拓扑结构（zeotypes）的沸石和相关材料可用于各种大规模应用，例如气体和液体分离、催化和离子交换。理想的沸石对应于由氧原子连接的四面体配位原子（T原子）的完美骨架。然而，有许多实际的沸石结构的例子，其中一些T原子的配位数（CN）是大于4，因为额外的非桥接物种键合到这些sites.本项目探讨这种沸石型材料与“更高的协调”T原子通过电子结构计算的分散校正的密度泛函理论（DFT）的框架。重点将放在两组材料上，即（1）含氟全硅沸石和（2）水合铝磷酸盐（AlPO）。在前一组中，氟阴离子共价键合到骨架Si原子上，形成三角-双锥SiO 4F-单元。在水合AlPO中，水与骨架Al原子的配位导致形成五配位或六配位的铝。虽然这两个基团都存在更高配位的T原子，但很大程度上仍然不清楚为什么它们的形成优先发生在某些位置。为了解决这个问题，DFT计算将用于阐明晶体化学因素，这些因素决定了结构中哪些T原子最容易假定配位数超过4。这些结构研究将通过基于DFT的振动性质预测来补充，以进一步了解主客体相互作用。此外，这些计算将用于识别指纹模式，表明在振动光谱中存在更高配位的T原子。对于含氟的全硅沸石，额外的分子动力学计算将用于研究氟阴离子无序。最后，含锗沸石中氟化物的键合和动力学将被研究，因为关于这些系统中GeO 4F-单元的存在一些相互矛盾的观察结果，该项目的主要目的是在基础水平上进一步理解具有更高配位T原子的沸石型系统。然而，可以预期，研究结果也将具有一定的应用相关性。例如，对氟阴离子结构导向特性的新认识可能有助于合理开发新的合成路线，对水合AlPO中骨架-水相互作用的更好的原子水平理解可以帮助解释这些材料的不同程度的水稳定性，这是各种应用的关键特性。