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Abstract |
With rising CO₂ levels in the atmosphere, turning this greenhouse gas into useful products through catalysis is a promising approach. This thesis explores catalytic materials including layered double hydroxides (LDHs), metal-organic frameworks (MOFs), and ZnO-based catalysts using advanced transmission electron microscopy (TEM). By combining conventional and in situ TEM, the research investigates how different synthesis methods, processing steps, and environmental conditions affect these materials at the nanoscale. For LDHs, TEM was used to study how variations in composition, aging, and mechanical treatment influence particle shape and structure. Among the materials studied, ZnAl LDH showed strong potential for CO₂ reduction reactions, despite showing layer defects. In situ experiments under heating and CO₂ exposure revealed morphological changes such as layer expansion and phase transformations, which help explain its catalytic behavior. In the case of MOFs, including M-MOF-74 (M = Cu, Zn), in situ studies showed signs of trapped atoms in the pores after the prescribed activation procedure and differences in thermal stability. CO₂ adsorption experiments revealed non-linear molecular arrangements and strong interactions, challenging existing assumptions and offering insight into the structural instability observed during desorption. The structure of a novel MOF, called UA-4, was solved using 3D electron diffraction after other methods failed. Enzyme-MOF hybrids were also studied, and a new staining technique was developed that made it possible to directly visualize enzymes inside the MOF framework using TEM for the first time. ZnO-based catalysts were examined after being synthesized through different methods, which produced a wide range of particle shapes, including nanorods, triangular forms, and herringbone-like structures. In situ oxidation studies faced challenges due to the formation of unwanted silicon oxide layers, highlighting the difficulties of studying materials in reactive environments. Overall, this work offers atomic-level insights into how catalyst structure influences performance. It contributes to the development of more efficient CO₂ conversion materials and addresses key challenges in using (in situ) TEM to study beam-sensitive and dynamic systems. The results support future efforts to design better catalysts and improve techniques for studying functional materials under realistic conditions. |
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