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

该项目的目的（在SPP的整个6年期间）是应用并进一步开发先进的电子断层扫描（ET）技术，用于催化应用中多孔结构的定量3D分析，目标是（i）有助于优化催化剂的合成和设计，以及（ii）直接使用3D数据对相关扩散和反应过程进行建模和模拟。该项目具有很强的方法重点，旨在将ET作为评估和改善催化应用孔结构的宝贵工具。除了ET，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。在第一个资助期内，安装了一个专用的360° ET保持器并投入运行，这允许在整个倾斜范围内进行倾斜系列，从而避免了ET衍生的3D重建中通常存在的缺失楔形伪影。平行于这个新的实现传统的ET已被应用于获得定量数据的三维孔结构的介孔TiO 2层。这些数据已经被用于气体通过这种真实的孔隙系统扩散的模拟研究。在第二个资助期内，FIB柱制备已经建立并应用于360° ET的中孔结构，提供了孔系统的改进的3D数据，而没有丢失楔形伪影。此外，已经设计了一种在FIB中使用操纵工具的新制备技术，其使得能够将单个（多孔）微米和纳米颗粒从TEM网格转移到360°断层扫描短柱的尖端上，从而使得能够对这种预选颗粒进行360°断层扫描而无需任何进一步的制备。该方法已成功地证明了具有开放大孔的微米级沸石颗粒以及显示封闭孔的中孔赤铁矿纳米颗粒（50 - 100 nm），并基于360° ET产生了孔网络的优异3D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，并将这种新技术应用于负载有催化纳米颗粒（例如Pt，Co 3 O 4）的多孔颗粒（例如沸石），用于特定的催化反应。这种粒子系统将由SPP内的合作伙伴提供。使用360° ET与先进的高分辨率TEM技术以及电子衍射相结合，预计可以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确切位置和可及性。这样的调查将有助于，一方面，以评估和优化这种负载颗粒的制造路线。另一方面，3D数据将用作使用这些颗粒作为基本构建块的分层催化剂结构建模的输入。

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.