Zeolites are microporous minerals of natural or synthetic origin. Their ability to act as tiny sieves that can selectively trap molecules in a cage-like structure makes them important industrial catalysts. However, in order to maximize their performance, both from an economic and sustainability standpoint, it's crucial to have an in-depth understanding of their chemical activity and structure. Therefore, researchers from the Central Laser Facility (CLF), University College London, Johnson Matthey, Argonne National Laboratory (US), and the Research Complex at Harwell combined three different imaging techniques to visualize the chemical properties of the framework.
For the study a commercialised zeolite called SSZ-13 was used. Confocal imaging, 3D fluorescence lifetime imaging, 3D multispectral fluorescence imaging and Raman mapping were carried out at the CLF's OCTOPUS Imaging Cluster and the Lasers for Science Facility to probe the chemically and structurally complex internal landscape of the material. Importantly, implementing a laser-based technique allowed the scientists to image organic carbonaceous deposits across the zeolite, which is notoriously challenging with electron microscopy techniques.
The research team focused on detemplation, the final step that takes place during the synthesis of zeolites where organic templating material (where organic material that acts as a shape template for the unique zeolite pore structure is removed from the framework) is removed from the framework via thermal combustion. As part of this process, a range of different organic species form due to decomposition, and although zeolites have been exploited commercially for several years, the intermediate steps of this process are not well understood. Through label-free multimodal imaging, the researchers were able to directly show for the first time in this model system images of organic material distributed across the crystal. Using fluorescence lifetime imaging microscopy (FLIM), they were also able to show how the framework can alter the lifetime of some deposits due to a geometric confinement effect.
The study is an exemplar of the potential of fluorescence imaging and bridges the gap on some of the fundamental questions related to zeolite synthesis. Additionally, the setup can be commercially exploited by industry to study other catalytic materials or run more in-depth studies on zeolites, so that they can be utilized to their full potential.
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