Research
Prof. Dr. Jörg Libuda
Physical Chemistry, University Erlangen-Nürnberg, Germany
Introduction:
Chemical reactions and physical processes at complex surfaces play a pivotal role in many areas of today’s technology including heterogeneous catalysis, energy technology, and environmental chemistry. Progress in these fields is of exceptional importance for the sustainability of development and, consequently, for the future development of society.In view this importance, it may appear surprising that, at the molecular level, today’s understanding of interface-related chemical processes in real systems is still poor.
The reason is that most real processes take place in enormously complex environments, both from a chemical and from a structural point of view. Often the reactive interfaces expose complex structures with characteristic length scales from few to hundreds of atoms, i.e. in the range of nanometers. The chemical properties of such "nanostructured" surfaces, can be quite different from their simple and extended counterparts. Numerous phenomena may arise, which may, for example, complete change the kinetics of a chemical reaction. In heterogeneous catalysis, but also in other fields, such phenomena are empirically utilized in order to maximize the selectivity or activity. At the molecular level, however, the origins of these changes are poorly understood. Some possible groups of effects are summarized in the figure for the specific example of a supported catalyst: The reactivity may change as a result of the influence of the support, due to changes in the electronic structure of small particles or due to the presence of specific reactive sites on small particles. Moreover, there are contributions due to coupling via surface diffusion, due to the confinement of adsorbates or due to restructuring and phase transformations of small particles (including oxidation processes).
The aim of the group is to provide an understanding of reaction kinetic and dynamics on complex and nanostructured surfaces at the microscopic level, including the development of concepts and models, which allow a quantitative and physically meaningful description of the underlying phenomena:
- Kinetics dynamics of chemical reactions at complex and nanostructured surfaces and in complex environments
- Time-resolved "in-situ" and "operando" spectroscopy at complex and nanostructured surfaces and materials
- Model studies and model development in heterogeneous catalysis, environmental, and energy technology
Embedded in numerous cooperations, both with academic groups and partners from industry, we aim at bridging the gaps between fundamental research and applied research.
Experiments:
The experimental strategy is based on the combination of well-defined model systems for complex surfaces and well-controlled kinetic experiments: The application of model surfaces, for example supported model catalysts in the field of heterogeneous catalysis, allows us to introduce specific aspects of real surfaces, without having to deal with their full complexity. Quantitative and well-controlled kinetic experiments, for example including molecular beam techniques, time-resolved in-situ surface vibrational spectroscopy and reactor experiments, provide us with the possibility to correlate the structural and chemical properties of the model surface with the corresponding chemical kinetics. We are also setting up reactor facilities combined with operando spectroscopies. As a result, detailed and quantitative insight can be obtained into structure-dependent microkinetics of a reaction, which finally can be utilized to develop microscopically well-founded kinetic models.
Some model systems and preparation methods:
- Compelex, but well-defined oxide films (growth in ultrahigh vacuum, UHV)
- Metal nanoparticles on oxide films (Physical Vapour Deposition, PVD)
- Bimetallic metal particles on oxide films (PVD)
- Lithographically prepared samples (cooperation with B. Kasemo)
- Nanoporous oxide films such as TiO2-Nanotube-Arrays (cooperation with P. Schmuki)
- Model systems for ionic liquid thin films (Model SILP, cooperation with P. Wasserscheid)
Experimental Systems:
"MOBY II"
A world-wide unique molecular beam / spectroscopy / reactor experiments been designed and set up, which allows us to perform most complex kinetic experiments in a quantitative, reproducible and fully remote-controlled fashion. The system is fully operational at the University of Erlangen-Nuremberg since 2007. Among other facilities, the system includes:
- One pulsed / chopped supersonic molecular beam source
- Four modulated effusive beam sources
- Vacuum-FT-IR-spectrometer for time resolved surface IR spectroscopy (TR-IRAS)
- Fast ion-counting quadrupole mass spectrometer (QMS) w. multichannel scaling
- Fast TR-IRAS-compatible pressure gap reactor
- High-pressure cell for polarization-dependent TR-IRAS
- Various preparation and characterization techniques for model surfaces (TPD, LEED, AES, etc.)
- Vacuum sample transfer system
"CIRCAT"
Currently, a new reactor / “operando”-spectroscopy system is under development within our activities in the Excellence Cluster “Engineering of Advanced Materials”. This system will bring together approaches to the preparation of catalytically active meterials from different projects within the Excellence Cluster, including single-crystal based model catalysts, porous materials and films, powders, ionic liquid films, heterogenized homogeneous catalysts and others.
The key features of the system will include:
- IRAS (IR Reflection Absorption Spectroscopy)
- TR-IRAS (Time Resolved IR Spectroscopy, including Step Scan FTIR and Rapid Scan FTIR)
- PM-IRAS (Polarization Modulation IRAS)
- TIRS (Transmission IR Spectroscopy)
- DRIFTS (Diffuse Reflection IR FT Spectroscopy)
- SFG (Sum Frequency Generation, w. Group of W. Peukert)
- Transient and Stationary Experiments (Pulse Gas Dosing and Laser Heating)
- Real-Time Mass Spectrometry
- Online High Sensitivity Gas Chromatography
- Vacuum Transfer of UHV-Prepared Model Catalysts
Research Highlights:
Current Projects:
Model NSR Storage Catalysts
Cooperation:
- Umicore AG & Co. KG, B. Kasemo, H. Grönbeck, M. Skoglundh, KCK (Göteborg, Sweden),
- A. Baraldi, Synchrotrone Elettra (Trieste, Italy),
- H.-J. Freund, Fritz-Haber-Institut der MPG (Berlin),
- F. Vines, A. Görling (Theoretical Chemistry, FAU Erlangen-Nuremberg)
- K. Neyman, Univ. Barcelona (Spain)
Model SOx Traps and Sulfur Poisoning
Cooperation:
- H. Grönbeck, M. Skoglundh, B. Kasemo, KCK (Göteborg, Sweden)
- F. Vines, A. Görling (Theoretical Chemistry, FAU Erlangen-Nuremberg)
CO2 and CH4 Activation: Controlling Selectivity via Nanostructuring
Cooperation:
- H.-P. Steinrück (FAU Erlangen)
- F. Illas (Univ. Barcelona)
Ceria Based Model Catalysts
Cooperation:
- V. Matolin, Chales University Prague (Czech Republic)
- A. M. Schneider, L. Hammer (Solid State Physics, FAU Erlangen-Nuremberg)
- K. Neyman, Univ. Barcelona (Spain)
Model SILP / SCILL Catalysts (Excellence Cluster 'Engineering of Advanced Materials')
Cooperation:
- P. Wasserscheid (FAU Erlangen)
- F. Maier, H.-P. Steinrück (FAU Erlangen)
- SÜD-CHEMIE AG
In-Situ / Operando Vibrational Spectroscopy (Excellence Cluster 'Engineering of Advanced Materials')
Cooperation:
- W. Peukert (Particle Technology, FAU Erlangen-Nuremberg)
- H.-P. Steinrück (Physical Chemistry, FAU Erlangen)
- W. Schwieger (Chemical Reaction Engineering)
Metal Loaded Titania Nanotube Arrays
Cooperation:
- P. Schmuki (Materials Science, FAU Erlangen-Nuremberg)
References:
The following review and introductory articles provide a good introduction to the experimental approach. For details concerning specific systems, we refer to the primary publications (full publication list):
