Electron microscopy group

Michael Scherzer, Frank Girgsdies, Eugen Stotz, Marc-Georg Willinger, Elias Frei, Robert Schlögl, Ullrich Pietsch, Thomas Lunkenbein

In situ GIXRD for electrochemistry. A electrochemical setup is combined with a GIXRD setup. Changes in the crystalline structure of the catalyst can be tracked during electrochemical operation. The recorded GIXRD pattern can be refined by Rietveld analysis. Cu surface oxidation was chosen to proof the concept
J. Phys. Chem. C, 2019, 123, 13253-13262.
DOI: 10.1021/acs.jpcc.9b00282
Liudmyla Masliuk, Manfred Swoboda, Gerardo Algara-Siller, Robert Schlögl, Thomas Lunkenbein

A setup to decouple catalytic reaction and atomic scale analysis inside the TEM is presented. The quasi in situ TEM grid reactor allows for identical location imaging of heterogeneous catalysts. The reactor, further, features relevant and homogeneous reaction conditions for the entire sample. Electron beam influence during the reaction can be entirely excluded. In addition, the catalytic conversion can be detected and reaction induced changes can be followed.
Ultramicrscopy, 2018, 195,  121-128.
DOI: 10.1016/j.ultramic.2018.09.001


Structural Complexity in Heterogeneous Catalysis: Cataloging Local Nanostructures

Liudmyla Masliuk, Marc Heggen, Johannes Noack, Franck Girgsdies, Annette Trunschke, Klaus E. Hermann, Marc G. Willinger, Robert Schlögl, and Thomas Lunkenbein

Quantification of individual defects: The study describes an analytical route toward a detailed and quantitative description of individual defects in heterogeneous catalysts. The investigation is based on high resolution scanning transmission electron microscopy (STEM) imaging using complex (Mo,V)Ox mixed oxide as an example. Tiling the structural regions simplifies the identification of local modifications in the microstructure. Using this technique we observed 19 different localized and extended structures that can be listed and classified into different structural motifs, intergrowth, channels, interstitial regions, and inclinations.
J. Phys. Chem. C, 2017, 121, 24093–24103.
DOI: 10.1021/acs.jpcc.7b08333
Katharina Mette, Stefanie Kühl, Andrey Tarasov, Marc G. Willinger, Jutta Kröhnert, Sabine Wrabetz, Annette Trunschke, Michael Scherzer, Frank Girgsdies, Hendrik Düdder, Kevin Kähler, Klaus Friedel Ortega, Martin Muhler, Robert Schlögl, Malte Behrens, and Thomas Lunkenbein

To coke or not to coke: Nonprecious-metal catalysts used for dry reforming of methane (DRM) deactivate by coking. The influence of structure and composition of nickel catalysts on the catalytic performance and coking affinity is described. High-resolution transmission electron microscopy (HR-TEM) revealed a nickel aluminate overgrowth. Catalysts with low Ni contents (5 mol %) exhibit predominantly oxidic surfaces dominated by Ni2+ and additionally some isolated Ni0 sites, which effectively diminishes the formation of coke during the DRM, while the activity is preserved. A large metallic Ni surface at high Ni contents (50 mol %) causes significant coke formation during the DRM.
ACS Catalysis. 2016, 6, 7238–7248.
DOI: 10.1021/acscatal.6b01683

Thomas Lunkenbein, Frank Girgsdies, Timur Kandemir, Nygil Thomas, Malte Behrens, Robert Schlögl, and Elias Frei

ZnO is the key for stability: Long-term stability tests of catalysts are often underestimated in academia, despite industrial requirements. The deactivation of an industrially relevant Cu/ZnO/Al2O3catalyst for the synthesis of methanol was investigated over a period of 148 days time-on-stream, with a combination of quasi in situ and ex situ analysis techniques. The findings indicate that controlling the polymorphism of ZnO is the key to the stability of the investigated catalytic system.
Angew. Chem. Int. Ed. 2016, 55, 12708–12712.
DOI: 10.1002/anie.201603368

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