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Inorganic Chemistry – Electron Microscopy Group

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Electron Microscopy Group:
Thomas Lunkenbein
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  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

J. Phys. Chem. C, 2017, 121, 24093–24103.
DOI: 10.1021/acs.jpcc.7b08333

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.

Topotactic Synthesis of Porous Cobalt Ferrite Platelets from a Layered Double Hydroxide Precursor and Their Application in Oxidation Catalysis

Klaus Friedel Ortega, Sven Anke, Soma Salamon, Fatih Özcan, Justus Heese, Corina Andronescu, Joachim Landers, Heiko Wende, Wolfgang Schuhmann, Martin Muhler, Thomas Lunkenbein, and Malte Behrens

Chem. Eur. J. 2017, 23, 12443 –12449.
DOI: 10.1002/chem.201702248

Holey hexagonal platelets of cobalt ferrite, CoFe2O4, can be obtained by co-precipitation and thermal decomposition of a layered double hydroxide (LDH) precursor. These particles are single crystalline and porous at the same time and show a topotactic relationship with the precursor. They are active as catalyst in alcohol oxidation and as electrocatalyst in the oxygen evolution reaction showing a clearly different behavior than commercial powder likely due to their unique microstructure.

Template Removal via Boudouard Equilibrium Allows for Synthesis of Mesostructured Molybdenum Compounds

Martin Schieder, Carina Bojer, Julia vom Stein, Sebastian Koch, Thomas Martin, Holger Schmalz, Josef Breu, and Thomas Lunkenbein

Angew. Chem. Int. Ed. 2017, 56, 13968-13972.
DOI: 10.1002/anie.201610786

The right balance: Mesostructuring of molybdenum compounds is hampered by fast gas-phase sintering of MoO3 obtained during the oxidative removal of templates. Taking advantage of the Boudouard equilibrium allows the oxygen fugacity to be maintained at a level where non-volatile MoO2-x is stable while carbonaceous material is oxidized by CO2. Mesostructured MoO2-x can subsequently be converted into MoO3 or MoN under retention of the mesostructure.

High-Temperature Stable Ni Nanoparticles for the Dry Reforming of Methane

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

ACS Catalysis. 2016, 6, 7238–7248.
DOI: 10.1021/acscatal.6b01683

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.

Bridging the Time Gap: A Copper/Zinc Oxide/Aluminum Oxide Catalyst for Methanol Synthesis Studied under Industrially Relevant Conditions and Time Scales

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

Angew. Chem. Int. Ed. 2016, 55, 12708–12712.
DOI: 10.1002/anie.201603368

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.

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