Quantitative 3D-analysis of real pore structures using advanced electron tomography techniques

该项目(在SPP的整个6年中)的目的是应用和进一步开发先进的电子断层扫描(ET)技术，用于催化应用的孔结构的定量3D分析，目的是(I)有助于催化剂的优化合成和设计，(Ii)直接使用3D数据对相关的扩散和反应过程进行建模和模拟。该项目有很强的方法学重点，旨在将ET作为评估和改善催化应用中孔结构的有价值的工具。除ET外，该项目还采用了其他的透射电子显微镜方法，以及扫描电子显微镜和聚焦离子束技术。在第一个资助期，安装并投入使用了专用的360°ET支架，它允许在整个倾斜范围内进行倾斜系列，从而避免在ET三维重建中丢失通常存在的楔形伪影。与这一新的实现相平行的是，传统的ET已经被应用于获得介孔TiO2层的3D孔结构的定量数据。这样的数据已经被用于对气体通过这种真实的孔隙系统扩散的模拟研究。在第二个资助期，已经建立了FIB柱制备，并将其应用于360°ET的介孔结构，提供了改进的孔系统3D数据，而不会丢失楔形伪影。此外，还设计了一种在FIB中使用操纵工具的新制备技术，该技术能够将单个(多孔)微米和纳米颗粒从透射电子显微镜网格转移到360°断层扫描存根的尖端，从而能够在不进行任何进一步准备的情况下对这种预先选择的颗粒进行360°断层扫描。该方法已成功地应用于具有开放大孔的微米级沸石颗粒以及显示闭孔的中孔赤铁矿纳米颗粒(50-100 nm)，并基于360°ET对孔网络进行了出色的三维重建。第三个资助期的主要目标是进一步建立单个颗粒转移和360°ET的组合应用，并将这一新技术应用于装载催化纳米颗粒(例如铂、Co3O4)的多孔颗粒(例如沸石)，以进行特定的催化反应。这样的粒子系统将由SPP内的合作伙伴提供。结合使用360°ET和先进的高分辨率电子显微镜技术以及电子衍射，有望精确地揭示这种载体颗粒的3D结构，特别是能够确定催化纳米颗粒在多孔网络中的准确位置和可获得性。这样的研究一方面将有助于评估和优化这种负载粒子的制备路线。另一方面，3D数据将被用作输入，以这种粒子作为基本构建块来建模分级催化剂结构。

The aim of the project (over the full 6 years of the SPP) is to apply and further develop advanced electron tomography (ET) techniques for quantitative 3D analysis of porous structures for catalytic applications with the goal to (i) contribute to an optimized synthesis and design of the catalyst and (ii) directly use the 3D data for modelling and simulation of relevant diffusion and reaction processes. The project has a strong methodological focus and aims at implementing ET as a valuable tool for evaluating and improving pore structures for catalytic applications. Apart from ET the project employs other transmission electron microscopy (TEM) methods as well as scanning electron microscopy (SEM) and focused ion beam (FIB) techniques. In the first funding period a dedicated 360° ET holder was installed and put into operation, which allows taking tilt series across the full tilt range thus avoiding missing wedge artefacts typically present in 3D reconstructions derived from ET. Parallel to this new implementation conventional ET has been applied to obtain quantitative data of the 3D pore structure of mesoporous TiO2 layers. Such data have already been used in modelling studies of gas diffusion through such real pore systems. In the second funding period FIB pillar preparation has been established and applied to mesoporous structures for 360° ET giving improved 3D data of the pore system without missing wedge artefacts. Moreover, a new preparation technique using manipulation tools in a FIB has been devised which enable the transfer of individual (porous) micro and nanoparticles from a TEM grid onto the tip of a 360° tomography stub thus enabling 360° tomography of such pre-selected particles without any further preparation. The method has been successfully demonstrated for micrometer sized zeolite particles with open macropores as well as for mesoporous hematite nanoparticles (50 - 100 nm) showing closed pores and resulted in excellent 3D reconstructions of the pore network based on 360° ET. The main goal of the third funding period is to further establish the combined application of individual particle transfer and 360° ET and to apply this new technique to porous particles (e.g. zeolites) loaded with catalytic nanoparticles (e.g. Pt, Co3O4) for specific catalytic reactions. Such particle systems will be provided by partners within the SPP. Using 360° ET in tandem with advanced high-resolution TEM technique as well as electron diffraction is expected to precisely reveal the 3D structure of such support particles enabling in particular the determination of the exact locations and accessibility of catalytic nanoparticles within the porous network. Such investigations will help, on the one hand, to evaluate and optimize the fabrication route of such loaded particles. On the other hand, the 3D data will be used as input for modelling of hierarchical catalyst structures using such particles as fundamental building blocks.