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Powder Diffraction and Surface Spectroscopy

The research activities of the group focus on crystallographic investigations inorganic functional materials. These are used either as catalysts in chemical reactions or for energy storage and conversion. Structure-property relationships are studied on different length scales: from the averaged crystal structure to the local structure of amorphous or disordered compounds. The group has a long experience in the field of in situ diffraction. For in situ or operando investigations of structure-property relationships a variety of different sample environments are available, which are listed under "Instrumental Equipment".

The following topics are addressed with the help of diffraction methods:

•    Phase identification, Rietveld refinements, quantitative phase analysis
•    Structural phase transformations
•    Crystal structure solution from powder diffraction data
•    Microstructure analysis
•    Catalytic reactions
•    Crystallization processes
•    Local structure analysis of amorphous or partially crystalline compounds

In addition to diffraction methods, the group also operates an X-ray photoelectron spectrometer (XPS) for the chemical characterization of solid surfaces. The instrument is additionally equipped with a UPS unit and thus allows the investigation of the electronic structure of the outer/valence or binding electrons. An in situ catalysis cell allows the analysis of reactive surfaces directly after a reaction without bringing the samples into contact with the ambient atmosphere.

The following questions are addressed with the help of XPS:

•    Identification of near-surface elements on the surface, element quantification
•    Determination of oxidation states
•    Identification of chemical environments
•    Determination of the work function of semiconductors or conductors

Vibrational spectroscopy is carried out using Raman spectroscopy. The spectrometer is equipped with a microscope, two different lasers and different reaction cells.

Besides own research activities, a part of the working group is responsible for operating service measurements. All diffractometers and spectrometers as well as the sample environments are offered for service measurements. In addition to sample preparation and execution of the experiments, the complete evaluation of the experimental data and their interpretation is made available to the customers.

Research activities:

•    In situ/operando studies of functional material for energy relevant processes
•    In situ studies on mechanochemistry/mechanocatalysis
•    Total scattering: pair-distribution function analysis of amorphous or partially crystalline materials
•    Spectroscopic investigations of solid catalysts

Claudia Weidenthaler

Priv.-Doz. Dr. Claudia Weidenthaler

April 2017
Guest professorship at the Taishan College, Shandong University / Jinan
April 2016
Guest professorship at the Taishan College, Shandong University / Jinan
2015
Habilitation at the University Duisburg-Essen (Habilitation treatise: Modern Powder Diffraction for Crystallographic Studies of Functional Materials)
2012
Group Leader at the Max-Planck-Institut für Kohlenforschung
since 1999
Senior scientist at the Max-Planck-Institut für Kohlenforschung
1998-1999
Scientist at the Universität Frankfurt
1995-1997
Scientist at the Universität Bremen
1995
Doctoral studies, Universität Mainz (Reinhard X. Fischer)
1984-1991
Study of Geology, Mineralogy and Crystallography, Universität Würzburg
1965
Born in Nittenau / Germany

Untersuchungsmethoden von Materialien unter „non ambient“ Bedingungen, Universität Bochum, WS2010/2011

Informations and documents can be found on the lecture website of Ruhr-Universität Bochum.

since 2020
Member of the „Project Review Panel (PRP)“ for “Powder Diffraction” at DESY
since 2020
Elected member of the advisory board of the German Mineralogical Society
since 2013
Expert of the International Energy Agency (IEA) Task 32 "Hydrogen-based energy storage" of the Hydrogen Implementation Agreement
since 2013
Spokeswomen of the workgroup "Materials science in crystallography“ of the DGK
 

Open Position 2019:
Open PhD position in the “Powder Diffraction and Surface Spectroscopy”

Universität Duisburg-Essen, Master of Science (Chemie) 3. Semester
„Moderne Beugungsmethoden für die Festkörperanalytik“
WiSe 2019/2020

Research Topics

In situ/operando studies of functional materials
In situ/operando studies of functional materials

In situ/operando studies of functional materials

The group deals with structural aspects of various inorganic solids, which are used in energy-relevant processes either as storage material, catalyst carrier material or catalysts.

•    Complex metal hydrides for solid hydrogen storage or as solid electrolytes in batteries
•    Catalysts for the catalytic cracking of ammonia, NH3, into hydrogen and nitrogen for fuel cell applications
•    Perovskites as electrode material in fuel cells or for catalytic water splitting
•    Oxide catalysts
•    Carbon materials for battery applications
•    Inorganic, polymer-based catalyst supports

The figure shows powder diagrams measured with a laboratory diffractometer during ammonia decomposition. Quantitative phase analyses allow to identify the changes of the catalyst precursor during the reaction and to correlate them with the ammonia decomposition.

Selected Publications:

Tseng, J.-C., Gu, D., Pistidda, C., Horstmann, C., Dornheim, M., Ternieden, J., & Weidenthaler, C. (2018). Tracking the Active Catalyst for Iron-Based Ammonia Decomposition by In Situ Synchrotron Diffraction Studies. ChemCatChem, 10(19), 4465-4472. doi:10.1002/cctc.201800398.

Weidenthaler, C. Crystal structure evolution of complex metal aluminum hydrides upon hydrogen release. Journal of Energy Chemistry, 42(3), 133-143. doi:10.1016/j.jechem.2019.05.026.

Weidenthaler, C., Felderhoff, M., Bernert, T., Sørby, M. H., Hauback, B. C., & Krech, D. (2018). Synthesis, Crystal Structure Analysis and Decomposition of RbAlH4. Crystals, 8(2): 103. doi:10.3390/cryst8020103.

Makepeace, J. W., He, T., Weidenthaler, C., Jensen, T. R., Chang, F., Vegge, T., Ngene, P., Kojima, Y., de Jongh, P. E., Chen, P., & David, W. I. (2019). Reversible ammonia-based and liquid organic hydrogen carriers for high-density hydrogen storage: Recent progress. International Journal of Hydrogen Energy, 44(15), 7746-7767.  doi:10.1016/j.ijhydene.2019.01.144.

Ortatatli, S., Ternieden, J., & Weidenthaler, C. (2018). Low Temperature Formation of Ruddlesden–Popper-Type Layered La2CoO4±δ Perovskite Monitored via In Situ X-ray Powder Diffraction. European Journal of Inorganic Chemistry, 2018(48), 5238-5245. doi:10.1002/ejic.201801162.

In situ studies on mechanochemistry/mechanocatalysis
In situ studies on mechanochemistry/mechanocatalysis

In situ studies on mechanochemistry/mechanocatalysis

The basic concept of mechanochemical processes is the introduction of energy, both for the activation of reactants and the catalysts used, by mechanical grinding instead of the supply of thermal or electrical energy. For potential applications this means that both temperature and pressure can be reduced compared to conditions applied in conventional reactors. A further advantage of mechanochemical processes is that solvents are largely or completely dispensed during the reaction. In earlier work of the Department of Heterogeneous Catalysis, catalysis experiments in ball-mills could be carried out without prior catalyst optimization. Although mechanochemistry and mechanocatalysis are becoming increasingly important in practice, the processes taking place during the grinding process are largely unknown.

in situ X-ray diffraction experiments allow the observation of structural phase changes or microstructural properties during a reaction (operando investigations). This requires an adaptation of the grinding jars to the experimental requirements of both the reaction and the respective beamline of the synchrotron. To obtain detailed information about mechanisms during mechanochemical reactions, in situ synchrotron diffraction experiments are combined with vibrational spectroscopy.

Selected Publications:

Amrute, A. P., Lodziana, Z., Schreyer, H., Weidenthaler, C., & Schüth, F. (2019). High-surface-area corundum by mechanochemically induced phase transformation of boehmite. Science, 366(6464), 485-489. doi:10.1126/science.aaw9377.
 

Total scattering: pair-distribution function analysis of amorphous or partially crystalline materials
Total scattering: pair-distribution function analysis of amorphous or partially crystalline materials

Total scattering: pair-distribution function analysis of amorphous or partially crystalline materials

Conventional X-ray diffraction experiments cannot provide detailed structural information about amorphous or partially crystalline disordered compounds. For amorphous or nanocrystalline samples, total scattering experiments can be used which take into account not only Bragg reflections but also diffuse scattering components. Pair distribution function curves (PDF) are obtained from the Fourier transformation of scattering data. These curves describe the distribution of interatomic distances between pairs of atoms and thus the local structure.

An example of the potential of PDF analyses are investigations on the formation of PtNi nano-alloys in porous graphitic hollow spheres, a material that has also been tested as electrode material in fuel cells. From temperature dependent PDF measurements, order and disorder phenomena of the alloy could be identified and correlated with heating and cooling rates. Another example are in situ PDF investigations on the crystallization of metal oxides, which can be used as photocatalysts. Both the formation of structural formation blocks from molecular precursors in highly diluted solutions and the temperature-dependent crystallization and phase transformation can be observed using in situ PDF analyses.

Selected publication:

Ş. Ortatatlı, Ş., Knossalla, J., Schüth, F., Weidenthaler, C. “Monitoring the formation of PtNi nanoalloys supported on hollow graphitic spheres using in situ pair distribution function analysis”, Phys. Chem. Chem. Phys., 2018, doi: 10.1039/c7cp07840d.
 

Spectroscopic investigations of solid catalysts
Spectroscopic investigations of solid catalysts

Spectroscopic investigations of solid catalysts

X-ray photoelectron spectroscopy (XPS) is used for the chemical characterization of surfaces. The method is based on the external photoelectric effect, in which photoelectrons are released from a solid by electromagnetic radiation. The kinetic energies of the photoelectrons are element-specific. Their measurement allows not only the qualitative and quantitative identification of elements, but also the determination of the chemical environment and the electronic structure of surface atoms. With the help of a combined heating/cooling unit in the analysis chamber itself, changes in sample surfaces can be observed spectroscopically in situ. A reaction cell is attached to the sample preparation chamber in which solid-gas reactions up to 900 °C can be performed. After the respective reaction the sample is brought into the analysis chamber without contact with the ambient atmosphere and spectroscopically examined.

The instrument is additionally equipped with a UV light source to generate photoelectrons in the sample surface. Ultraviolet photoelectron spectroscopy (UPS) analyzes the Density of States (DOS) of a compound and thus serves to determine the valence band structure of surfaces and adsorbates.

Raman spectroscopy is an excellent method to observe local structural changes of catalysts in heterogeneous catalysis. This includes structural changes during a crystallization process as well as structural changes during a catalytic reaction itself. The data can help to identify intermediates and products of a heterogeneously catalyzed reaction or to elucidate reaction mechanisms. In addition, defects in the local crystal structure can be observed, which makes Raman spectroscopy a valuable method for the investigation of nanomaterials. The spectrometer is equipped with two different sample environments that allow in situ spectroscopy of a solid during heating or cooling or during a gas phase reaction.
 

 

Instrumental Equipment

X-ray Photoelectronspectroscopy (XPS)
X-ray Photoelectronspectroscopy (XPS)

X-ray Photoelectronspectroscopy (XPS)

XPS is a method based on the photoelectric process for quantifying the chemical composition of surfaces, determining oxidation states and analyzing the chemical environment of elements.

The spectrometer (SPECS GmbH) is equipped with a dual anode (Al/Mg) as well as a monochromatic Al/Ag source. In the analysis chamber samples can be heated or cooled during spectroscopic measurements. The use of an electron gun for charge compensation allows the analysis of electrically non-conductive samples with high spectral resolution.

The spectrometer is additionally equipped with a UV source for measuring UPS spectra.

To avoid contact of samples after chemical reactions with the atmosphere, temperature dependent reactions of solid surfaces with different reaction gases can be performed in a reaction chamber attached to the XPS. After a reaction, the sample can be transferred directly into the analysis chamber under exclusion of air and measured.
 

Renishaw inVia Raman spectrometer
Renishaw inVia Raman spectrometer

Renishaw inVia Raman spectrometer

Raman spectroscopy is based on the interaction of monochromatized light with matter and provides insights into the mean local structure of compounds, defects, and crystallization processes.

The inVia Raman spectrometer (Renishaw GmbH, Pliezhausen, Germany) is equipped with two lasers with wavelengths of 785 and 532 nm. The tunability of the laser intensity allows the investigation of laser-sensitive materials. Optics specially matched to the lasers and the CCD area detector ensures high spectral resolution.

Two measuring cells are available for in situ measurements. They allow the investigation of structure-property relationships as a function of temperature and the performance of solid-gas reaction reactions. For in situ measurements, the instrument can be equipped with either the THMS 600 cell, allowing measurements in the temperature range between -196°C zo 600°C or the CCR1000 catalytic cell reactor, which covers a temperature range from 25°C to 1000°C in different gas atmospheres.
 

Stoe STADI P transmission powder diffractometer
Stoe STADI P transmission powder diffractometer

Stoe STADI P transmission powder diffractometer

The double measuring station diffractometer is equipped with a molybdenum X-ray source, germanium primary monochromators, as well as a linear PSD (Stoe) and a Mythen detector.

For in situ investigations a measuring station is equipped with a STOE high-temperature furnace, which allows measurements of samples in quartz glass capillaries under inert gas atmosphere up to 900 °C. At the second measuring station diffraction data can be collected at room temperature as well as at low temperatures up to 100 K. In addition, measurements in a special sample chamber under high gas pressures are possible.
 

X'Pert PRO powder diffractometer (PANalytical)
X'Pert PRO powder diffractometer (PANalytical)

X'Pert PRO powder diffractometer (PANalytical)

The working group operates two diffractometers with copper X-rays, which can be used with primary monochromator, hybrid monochromator for capillary measurements as well as divergence slit optics for conventional Bragg-Brentano geometry. The data collection is performed with the aid of X'Celerator detectors.

Both diffractometers are equipped with a reaction chamber (Anton Paar XRK900) for in situ measurements under reaction conditions. The gas flows are adjusted using computerized mass flow controllers. The composition of the product gases can be analyzed directly in a connected gas chromatograph.
 

Rigaku
Rigaku

Rigaku

The SmartLab is equipped with a 9 kW rotating anode for the generation of X-rays. A Johannson monochromator with appropriate optics generates monochromatic radiation for operation in transmission geometry, the 2D detector HyPix3000 allows fast data collection. The reaction chamber ReactorX allows in situ measurements of samples under different gas atmospheres and reaction temperatures.

In situ sample environments
In situ sample environments

In situ sample environments

Different sample environments allow structural investigations under various environmental conditions such as increased H2 pressures, variable temperatures in the range of liquid nitrogen up to 950 °C, or in a gas flow.

 

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