In situ Characterization of Catalysts for Sustainable Energy Production

Monia Runge Nielsen

Research output: Book/ReportPh.D. thesisResearch

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Abstract

This work presents the studies of catalyst nanoparticles with particular focus on dynamic processes. Since the catalytic ability of the catalyst resides on the surface, the key to develop new and improved catalysts is to understand the relation between the atomic configuration of the catalyst surfaces and their activity. Transmission electron microscopy is able to visualize the nanostructure with atomic resolution and thereby reveals the atomic configuration of the surface of the nanoparticles. In the present work, both an environmental transmission electron microscopy and a high pressure holder were used to study nanoparticles in situ at elevated temperature, with gases at different pressures in order to recreate the conditions found in a reactor. The environmental transmission electron microscope is going to pressures of a few mbar, and the nanoreactor is reaching atmospheric pressure. These in situ studies of catalysts are essential, since the gas atmosphere, the pressure and the temperature are all known to influence the structure of the catalyst.
The motivation of this study is the catalytic conversion of syngas into higher alcohols and two approaches are presented.
The first approach is looking at rhodium nanoparticles on different support. This was carried out as part of a bigger collaboration, where transmission electron microscopy was used to assist the development of new and improved catalysts by characterization. In addition, in situ studies of the system was performed, where the interaction between the nanoparticles and the support is addressed. However, the majority of the time was spent to start up a newly acquired high pressure holder, i.e. to identify some of the challenges imposed on the system, to help figure out what is going on and to suggest which changes are necessary to improve the system.
The second approach is looking at the activation of iron oxide for Fischer-Tropsch synthesis (not FTS itself). Since the activated metallic iron catalysts are rapidly restructured after exposure to even trace amount of oxygen or water, in situ characterization is necessary to follow during reaction conditions. A variety of different in situ experimental methods was used. Following the structural evolution of iron oxide under reaction conditions with X-ray electron diffraction, the crystal structures of the phases present during reduction and carburization were identified. In situ TEM was used to probe any changes in the structure or in the chemical properties of an individual Fe nanoparticle during reduction or carburization and to monitor the processes at the nanoscale and under reaction conditions. This was combined with in situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy to directly follow the carburization process, to determine whether the formation takes place on the surface or in bulk.
Original languageEnglish
PublisherDTU Nanolab
Number of pages181
Publication statusPublished - 2019

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