Characterization of extra-framework species in zeolites

Research output: ResearchPh.D. thesis

Sometimes it is difficult to see the wood for the trees. Crystallography is a great tool to take a step back, to observe and analyze the effects and implications caused by atoms and molecules in a crystalline material. In catalysis, the goal is to uncover the chemical pathway from reactant to product, which usually makes research focus on molecular changes and step reactions. In other words, local atomic and molecular properties. However, the frame surrounding these local effects is a crucial prerequisite to understand their implications and individual contribution.
In this PhD dissertation I use crystallography as my tool to delve into a crystalline material used for catalysis. Zeolites are introduced in PART I, where the main characterization techniques and methods are also outlined. At the heart of crystallography is the diffraction technique. I use diffraction extensively, applying both simple analysis methods, such as Rietveld structural analysis, as well as more advanced methods, such as the maximum entropy method and electrostatic potential analysis.
PART II covers the main research results obtained during my PhD of the chabazite zeolite. When loaded with copper, the zeolite is a highly active, selective, and thermally stable catalyst, which is commercially used in ammonia-assisted selective catalytic reduction of environmentally hazardous NO and NO2 gasses.
Firstly, a structure solution is conducted, successfully locating a novel copper site. In order to locate this site, the challenge of finding it in the unit cell, is overcome by a combination of characterization methods to analyze high-resolution synchrotron X-ray diffraction data. Secondly, the improved structure model as well as other established models are applied to a series of metal-loaded and protonated chabazite zeolites for an in-depth structural exploration. The amount of information that can be retrieved using such excellent data is pushed to the limit.
Finally, combined diffraction and absorption experiments were performed in situ on copper-loaded chabazite zeolite. Catalytic intermediate species are investigated in a collaborative study, where the main analysis was performed during my stay abroad in Turin, Italy. This revealed that reduction of Cu2+ to Cu+ is correlated with a copper migration. Furthermore, the reduction may occur in an oxidative atmosphere, and a novel copper site is found exclusively for monovalent Cu+.
Original languageEnglish
PublisherAarhus Universitet
Number of pages174
StatePublished - 19 Jan 2018

    Research areas

  • Zeolites, Chabazite, Powder X-ray Diffraction, XANES

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