Advancing Novel Transmission Electron Microscopy Techniques for Atomic Scale Catalyst Characterization

Catalysis plays a vital role in modern society, involved in key processes in chemical production, environmental protection, and energy conversion. Their importance in the green transition is exemplified in the emerging technologies, Power-to-X and CO₂-capture. Transmission Electron Microscopy (TEM) is an integral part of catalysis research, providing atomic scale information on the morphology and elemental composition of the catalysts. Despite recent developments in TEM methodology, limitations persist. Limitations include unwanted electron beam effects and gaps in measurement conditions between TEM and catalysis experiments, which restrict the use of TEM in catalysis research.
In this thesis, methodological advancements in TEM for catalysis characterization are presented, centered around three projects.

The first project presents a structure-property relationship explaining why 3 nm gold nanoparticles are most selective towards carbon monoxide in the electrochemical reduction of carbon dioxide. Through a novel combination of TEM methods, the abundance of surface sites pinned to twin boundaries was linked to the carbon monoxide selectivity of the gold nanoparticles sized between 1.5 and 6.5 nm.

In another study, state-of-the-art in situ TEM is utilized in an attempt to develop a novel TEM method for characterizing catalysts by imaging a catalyzed chemical reaction. Preliminary results are presented, showing an adlayer formed under a carbon monoxide atmosphere on 5 nm platinum nanoparticles. Initial checks, such as bond length and reversibility, are consistent with a carbon monoxide adlayer, while others point in a different direction. This may represent the first direct observation of such a layer on Pt nanoparticles, which would be the first step needed in the development of the novel method.

In the final study, a novel developed electrostatic beam blanker is introduced to mitigate beam damage in molybdenum disulfide, a two-dimensional catalyst used at an industrial scale. By temporally controlling electron arrival to 12 ns intervals separated by 1 µs, beam damage was reduced by an average of 44 ± 18 %-points at a dose rate of 0.7 e/(Ų · s), compared to data acquired with no temporal control. A similar effect was not observed for a dose rate of 0.3 e/(Ų · s) and 3.0 e/(Ų · s). The beam blanker was further utilized in an imaging setting, demonstrating that atomic resolution of molybdenum disulfide is achievable in a blanked mode.

The work presented here is based on nanoparticles of gold and platinum, as well as two-dimensional molybdenum disulfide, which serve as model systems in catalysis research. These findings concurrently demonstrate why TEM is a powerful tool in catalysis research and point towards potential advancements of the method, thereby enhancing the search for new and better catalysts.