Electrocatalysis at Surfaces
The main objective of our group is a molecular level understanding of catalytic processes on heterogeneous catalyst surfaces. For that purpose we are utilizing well-defined model systems based on metal single crystals, oxide thin films, and supported metal nanoparticles to study the elemental steps of catalytic reactions. Especially we are interested in the catalytic properties of bimetallic surfaces and nanoparticles. It is well known that e.g. alloys can have very different properties from the constituting metals. For example, PdZn alloys are very good catalysts for methanol steam reforming whereas Pd alone predominantly catalysis methanol decomposition and Zn is not an active catalyst for this reaction.
We are characterizing our model systems in terms of surface structure by Scanning Tunneling Microscopy (STM), Low Energy Ion Scattering (LEIS), and Low Energy Electron Diffraction (LEED). Their chemical composition and electronic properties are obtained by photoelectron spectroscopy (XPS, AES). Available adsorption sites, adsorption/desorption energies, reaction intermediates and possible mechanisms are tested by the adsorption of reactants or probe molecules followed by Infrared - and Temperature Programmed Desorption Spectroscopy (TDS).
To overcome the problems that may arise upon transferring conclusions gained under UHV to a technical catalytic process we are testing the catalytic properties (activity, selectivity) by a combination of reaction analysis (by MS or micro GC) and in-situ Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRAS) and Sum Frequency Generation (SFG) operating from UHV to atmospheric (∼reaction) conditions. Additionally, we have access to in-situ NAP-XPS and EXAFS at synchrotron facilities.
Only the combination of all methods enables us to draw an almost complete picture of what is going on at the surface during the catalytic process and which parameters are influencing the properties of the catalyst.
The combination of surface science techniques with advanced in-situ spectroscopic methods helps us to compare the results obtained from the simplified model systems with industrial grade high surface area powder catalysts.
Our current research projects:
- Methanol Synthesis on Cu based model catalysts (Cu/ZnO, Cu/CeO2) studied by in-situ spectroscopy.
- Dry Reforming - from understanding the elementary steps to better catalysts
- Cobalt Oxide Model Catalysis Across the Materials and Pressure Gap
- SFB-FOXSI Functional Oxide Surfaces and Interfaces; in-situ spectroscopy of chemical reactions on pure and doped ZrO2 thin films and zirconia-based metal-oxide systems
- Supported Pt nanoparticles as model catalysts
- Nanoparticle Exsolution: Tailoring the Catalytic Reactivity of Perovskite Type Catalyst Materials in Real Time by Polarization (i.e. applied voltage)
For the studied catalytic reactions, we have a strong focus on environmental protection and sustainable energy production (chemical energy conversion). For example, automotive exhaust gas cleaning, or the utilization and activation of CO2 (Power 2 Gas or Power 2 Fuel). Due to the equilibrium nature of catalytic reactions (and as specific catalyst materials are used for both, synthesis and reforming) we try to study both reaction directions on our model catalysts.
|Water Splitting||2 H2O ⇌ 2 H2 + O2|
|Water Gas Shift||CO + H2O ⇌ CO2 + H2||reverse WGS|
|Methanol Reforming||CH3OH + H2O ⇌ 3 H2 + CO2||Methanol Synthesis|
|CO2 Electrolysis||2 CO2 ⇌ 2 CO + O2||CO Oxidation|
|Methane dry reforming||CH4 + CO2 → 2 CO + 2 H2|
Lab based in-situ NAP-XPS
Our in situ Near Ambient Pressure XPS (NAP-XPS) system was specially developed for (model) catalyst investigations under reaction conditions. As our current ERC project focuses on electro-catalysis (i.e. sustainable fuel production and chemical energy conversion utilizing fuel cell technology) we particularly designed the sample stage/sample holder to enable catalytic testing with simultaneous electrochemical characterization (3 electrode geometry, laser heating system with temperatures up to 1000°C).
To enable a direct correlation of catalysis with surface structure and electrochemical properties the spectroscopic cell can be operated in flow mode. Online reaction analysis is done by mass spectrometry (MS) and gas chromatography (micro GC). Electrochemical characterisation is achieved via electrochemical impedance spectroscopy (EIS) and by recording current voltage (IV) curves.
With this unique combination of the above-mentioned methods in one system, it is possible to gain information on the performance and surface properties of investigated catalysts in real time.
With our modular sample holder design and the laser heating system it is possible to study a wide variety of samples (e.g. singly crystals, thin films, foils, industrial catalysts). A load lock enables fast sample transfer into and out of the system. Furthermore, the sample stage is exchangeable, giving us the opportunity for constant developments to meet the needs of new projects.
© AG Rameshan
1. C. Rameshan, W. Stadlmayr, C. Weilach, S. Penner, H. Lorenz, M. Hävecker, R. Blume, T. Rocha, D. Teschner, A. Knop-Gericke, R. Schlögl, N. Memmel, D. Zemlyanow, G. Rupprechter, B. Klötzer
"Subsurface-controlled CO2-selectivity of PdZn near surface alloys in H2 generation by methanol steam reforming"
Angewandte Chemie International Edition 94 (2010), 3224.
2. Christoph Rameshan, Werner Stadlmayr, Simon Penner, Harald Lorenz, Norbert Memmel, Michael Hävecker, Raoul Blume, Detre Teschner, Tulio Rocha, Dmitry Zemlyanov, Axel Knop-Gericke, Robert Schlögl, Bernhard Klötzer
"Hydrogen Production by Methanol Steam Reforming on Copper Boosted by Zinc-Assisted Water Activation"
Angewandte Chemie International Edition 41 (2012), 3002 - 3006.
3. H. Li, J. Choi, W. Mayr-Schmölzer, C Weilach, C. Rameshan, F. Mittendorfer, J. Redinger, M. Schmid, G. Rupprechter:
"The growth of an ultrathin zirconia film on Pt3Zr examined by-HR-XPS, TPD, STM and DFT";
Journal of Physical Chemistry C, 119 (2015), S. 2462 - 2470.
4. C. Rameshan, M. Ling Ng, A. Shavorskiy, J. Newberg, H. Bluhm:
"Water adsorption on polycrystalline vanadium from ultra-high vacuum to ambient relative humidity";
Surface Science, 641 (2015), S. 141 - 147.
Lorenz Lindenthal BSc
Janko Popovic BSc
Thomas Haunold BSc Ph.D. Student
Harald Summerer BSc Ph.D. Student
Raffael Rameshan MSc Forscher
Thomas Ruh MSc Forscher
Xia Li, Ph.D.
Verena Pramhaas Ph.D.
Former group members
Dr. Abhijit Bera
Dr. Andrey V. Bukhtiyarov
Motin Md. Abdul Ph.D
Dr. Harald Helmuth Holzapfel
Dr. Hao Li
Dr. Kresimir Anic
Dr. Matteo Roiaz
Prof. Konstantin Neyman, opens an external URL in a new window, Departament de Química Física & Institut de Química Teòrica i Computacional (IQTC-UB), Universitat de Barcelona, Spain
Prof. Andreas Stierle, opens an external URL in a new window, DESY Nanolab and University of Hamburg, Germany
Assoz. Prof. Bernhard Klötzer, opens an external URL in a new window, Institut für Physikalische Chemie, Universität Innsbruck, Austria
Dr. Erik Vesselli, opens an external URL in a new window, Dipartimento di Fisica, Università degli Studi di Trieste / IOM-CNR Laboratorio TASC
Dr. Hendrik Bluhm, Advanced Light Source, Lawrence BerkeleyNational Laboratory, Berkeley, USA
Prof. Ulrike Diebold, opens an external URL in a new window, Dr. Gareth Parkinson, opens an external URL in a new window, Institut für Angewandte Physik, TU Wien
Prof. Jörg Libuda, opens an external URL in a new window, Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
Jürgen Fleig / Alex Opitz, Institute of Chemical Technologies and Analytics, Electrochemistry Devision, Technische Universität Wien, Austria
Andrey V. Bukhtiyarov, Boreskov Institute of Catalysis SB RAS, opens an external URL in a new window, Novosibirsk, Russia
© Christoph Rameshan
Head of Research Group
Mag.rer.nat. Dr.rer.nat. Christoph Rameshan