Instituto de Tecnología Química, Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas, Valencia, Spain.
Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, Cádiz, Spain.
Nat Protoc. 2021 Apr;16(4):1871-1906. doi: 10.1038/s41596-020-0366-9. Epub 2020 Sep 4.
The encapsulation of subnanometric metal entities (isolated metal atoms and metal clusters with a few atoms) in porous materials such as zeolites can be an effective strategy for the stabilization of those metal species and therefore can be further used for a variety of catalytic reactions. However, owing to the complexity of zeolite structures and their low stability under the electron beam, it is challenging to obtain atomic-level structural information of the subnanometric metal species encapsulated in zeolite crystallites. In this protocol, we show the application of a scanning transmission electron microscopy (STEM) technique that records simultaneously the high-angle annular dark-field (HAADF) images and integrated differential phase-contrast (iDPC) images for structural characterization of subnanometric Pt and Sn species within MFI zeolite. The approach relies on the use of a computational model to simulate results obtained under different conditions where the metals are present in different positions within the zeolite. This imaging technique allows to obtain simultaneously the spatial information of heavy elements (Pt and Sn in this work) and the zeolite framework structure, enabling direct determination of the location of the subnanometric metal species. Moreover, we also present the combination of other spectroscopy techniques as complementary tools for the STEM-iDPC imaging technique to obtain global understanding and insights on the spatial distributions of subnanometric metal species in zeolite structure. These structural insights can provide guidelines for the rational design of uniform metal-zeolite materials for catalytic applications.
将亚纳米尺度的金属实体（孤立金属原子和少数原子的金属团簇）封装在多孔材料（如沸石）中，是稳定这些金属物种的有效策略，因此可以进一步用于各种催化反应。然而，由于沸石结构的复杂性及其在电子束下的低稳定性，很难获得封装在沸石晶体内的亚纳米尺度金属物种的原子级结构信息。在本方案中，我们展示了一种扫描透射电子显微镜（STEM）技术的应用，该技术可同时记录高角度环形暗场（HAADF）图像和积分差分相衬（iDPC）图像，用于对 MFI 沸石中的亚纳米 Pt 和 Sn 物种进行结构表征。该方法依赖于使用计算模型来模拟在金属处于沸石不同位置的不同条件下获得的结果。这种成像技术可以同时获得重元素（在本工作中为 Pt 和 Sn）和沸石骨架结构的空间信息，从而能够直接确定亚纳米尺度金属物种的位置。此外，我们还介绍了将其他光谱技术与 STEM-iDPC 成像技术相结合，作为获得沸石结构中亚纳米尺度金属物种空间分布的全局理解和深入了解的补充工具。这些结构上的见解可以为催化应用中均匀金属-沸石材料的合理设计提供指导。
