Institute of Materials Chemistry
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Head of researchgroup

Univ.Ass. Mag.rer.nat. Dr.rer.nat. Christoph Rameshan

Address:
Getreidemarkt 9/165
1060 Wien
Austria

Tel.: +43/1/58801-165115
Fax: +43/1/58801-165980

e-mail: christoph.rameshan@tuwien.ac.at

Publications

curriculum vitae

Research Interests

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

Instrumentation

XPS/PM-IRAS Setup

Its main purpose is model catalyst preparation and characterisation and to investigate their properties for heterogeneous catalysis. The setup is custom build, with a high pressure cell for Polarisation Modulation Infrared Reflectance Absorption Spectroscopy (PM-IRAS) measurements (pressure range 10-9 mbar – 1000 mbar) to bridge the prominent gap between UHV and ambient conditions (“pressure gap”). It includes a UHV preparation chamber for sample preparation and characterisation with LEED, XPS, AUGER and TPD. The system is also equipped with gas dosing units and PVD evaporators. After preparation samples can be transferred to the high pressure cell. The cell is designed as circulating batch reactor. At catalytic reactions conditions adsorbed species can be identified on the model catalyst surface. Due to a special sample holder and mounting design we can operate in the temperature range 77 – 1200 K.

Figure 2: XPS/HT-STM Setup

XPS/HT-STM Setup

The system is an extended STM setup from SPECS (Germany) with 3 chambers for STM, sample preparation and a load lock for fast sample transfer into and out of UHV. The preparation chamber is equipped with LEED, TPD, hemispherical analyser and instruments for XPS, AUGER and LEIS measurements. Furthermore the system is equipped with gas dosing units and PVD evaporators. The setup is dedicated to model catalyst preparation and characterisation in UHV.

Figure 3: SFG-Setup “DAISI” with laser optics and UHV + spectroscopic cell.

SFG-Setup

The setup is dedicated to model catalysts preparation and characterisation, from single crystals up to supported nanoparticles, and to study their interaction with reactive gases. The setup is comprised of three parts: a UHV preparation chamber, a load lock for fast sample transfer and a spectroscopic cell for investigations under realistic catalytic conditions. The preparation chamber is equipped with the standard tools of surface science: an ion gun, gas dosing, PVD evaporator, mass spectrometer (for TPD) and LEED + Auger optics. Samples can be transferred without breaking the vacuum to the spectroscopic cell which allows to perform SFG (sum frequency generation) spectroscopy under reaction conditions. The cell is designed as circulating batch reactor with the possibility of gas analysis via MS. SFG probes vibrationally the sample in the 1000-4500 cm-1 range and provides inherently surface specific information about the species adsorbed on the specimen. Therefore it can be applied from UHV to ambient pressure and bridges the well-known gap between the classical UHV studies and real catalysis.

Figure 4: Microreactor

Microreactor

In heterogeneous catalysis it is of high interest to investigate how single or polycrystalline model catalysts, whose surfaces have already been prepared and characterised, behave under reaction conditions (i.e. elevated pressure and temperature). This behaviour is reflected by kinetic parameters such as conversion, yield, catalytic productivity and selectivity. Commercially available systems feature reaction volumes which surpass the catalytically active surface area of model catalysts by orders of magnitude, thus lowering the detection sensitivity of reaction gases tremendously. To solve this problem a new system for both catalyst preparation under UHV and performance of reactions on the catalyst’s surface (up to 1 bar) within a dense, dismountable micro reactor was developed. The small cell volume (i.e. cell in cell design) of the continuous flow reactor allows excellent catalytic characterisation of model catalysts.

Selected Publications

1. Subsurface-controlled CO2-selectivity of PdZn near surface alloys in H2 generation by methanol steam reforming
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
Angewandte Chemie International Edition 94 (2010), 3224
DOI: 10.1002/anie.200905815

 

 

 

2. Hydrogen Production by Methanol Steam Reforming on Copper Boosted by Zinc-Assisted Water Activation
C. Rameshan, W. Stadlmayr, S. Penner, H. Lorenz, N. Memmel, M. Hävecker, R. Blume, D. Teschner, T. Rocha, D. Zemlyanov, A. Knop-Gericke, R. Schlögl, B. Klötzer
Angewandte Chemie International Edition 41 (2012), 3002
DOI: 10.1002/anie.201106591

3. The growth of an ultrathin zirconia film on Pt3Zr examined by-HR-XPS, TPD, STM and DFT
H. Li, J. Choi, W. Mayr-Schmölzer, C Weilach, C. Rameshan, F. Mittendorfer, J. Redinger, M. Schmid, G. Rupprechter:
Journal of Physical Chemistry C, 119 (2015), 2462
DOI: 10.1021/jp5100846

4. Enhancing Electrochemical Water-Splitting Kinetics by Polarization-Driven Formation of Near-Surface Iron(0): An In Situ XPS Study on Perovskite-Type Electrodes
A.K. Opitz, A. Nenning, Ch. Rameshan, R. Rameshan, R. Blume, M. Hävecker, A. Knop-Gericke, G. Rupprechter, J. Fleig, B. Klötzer
Angewandte Chemie - International Edition, 54 (2015), 2628
DOI: 10.1002/anie.201409527

5.) CO Adsorption on Reconstructed Ir(100) Surfaces from UHV to mbar Pressure: A LEED, TPD, and PM-IRAS Study
K. Anic, A. V. Bukhtiyarov, H. Li, C. Rameshan, G. Rupprechter
J. Phys. Chem. C, 2016, 120 (20), 10838
DOI: 10.1021/acs.jpcc.5b12494

Group Members

Aktuell:

Dipl Ing. Kresimir AnicPh.D. Student
Thomas Haunold BScstudent research assistant
Matteo Roiaz MSc.Ph.D. Student
Verena Pramhaas MSc.Ph.D. Student
Xia Li, Ph.D.Postdoc
Motin Md. Abdul Ph.DPostdoc
Bera Abhijit Ph.DPostdoc

 

Former Group Members

  • PhD Students
    • Dr. Harald Helmuth Holzapfel
    • Dr. Hao Li

  • Bachelor Students
    • Lorentz Lindenthal
    • Harald Summerer
    • Janko Popovic

Cooperation Partners

Prof. Günther Rupprechter, Institute of Materials Chemistry, TU Wien

Prof. Konstantin Neyman, Departament de Química Física & Institut de Química Teòrica i Computacional (IQTC-UB), Universitat de Barcelona, Spain

Prof. Andreas Stierle, DESY Nanolab and University of Hamburg, Germany

Assoz. Prof. Bernhard Klötzer, Institut für Physikalische Chemie, Universität Innsbruck, Austria

Dr. Erik Vesselli, 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, Dr. Gareth Parkinson, Institut für Angewandte Physik, TU Wien

Prof. Jörg Libuda, 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, Novosibirsk, Russia

SFB "Functional Oxide Surfaces and Interfaces (FOXSI)"