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

该项目的目标（在SPP的整整6年时间里）是应用并进一步发展先进的电子断层扫描（ET）技术，用于催化应用的多孔结构的定量3D分析，目标是：(i)有助于催化剂的优化合成和设计，（ii）直接使用3D数据进行相关扩散和反应过程的建模和模拟。该项目具有很强的方法论重点，旨在实施ET作为评估和改进催化应用的孔结构的有价值的工具。除了ET外，该项目还采用了其他透射电子显微镜（TEM）方法以及扫描电子显微镜（SEM）和聚焦离子束（FIB）技术。在第一个资助阶段，安装了一个专用的360°ET支架并投入使用，它允许在整个倾斜范围内进行倾斜系列，从而避免了在ET三维重建中通常出现的楔形人工制品的缺失。与此同时，传统的ET已被应用于获得介孔TiO2层的三维孔隙结构的定量数据。这些数据已经被用于模拟研究气体通过这种真实孔隙系统的扩散。在第二个资助期，FIB柱制备已经建立并应用于360°ET的介孔结构，提供了改进的孔隙系统三维数据，而没有遗漏楔形人工制品。此外，在FIB中使用操作工具的一种新的制备技术已经被设计出来，该技术可以将单个（多孔）微粒子和纳米颗粒从TEM网格转移到360°断层扫描存根的尖端，从而实现360°断层扫描，而无需任何进一步的制备。该方法已经成功地应用于微米大小的具有开放大孔的沸石颗粒和具有封闭孔的介孔赤铁矿纳米颗粒（50 - 100 nm），并基于360°ET获得了极好的孔隙网络三维重建。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的联合应用，并将这项新技术应用于负载催化剂的多孔颗粒（如沸石）纳米颗粒（如铂，Co3O4）用于特定的催化反应。这种颗粒系统将由SPP的合作伙伴提供，利用360°ET与先进的高分辨率TEM技术以及电子衍射技术相结合，有望精确揭示这种支撑颗粒的3D结构，特别是能够确定多孔网络中催化纳米颗粒的确切位置和可及性。这些研究一方面将有助于评估和优化这种负载粒子的制造路线。另一方面，3D数据将用作分层催化剂结构建模的输入，使用这些粒子作为基本构建块。

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.