Monitoring of Electrochemical Processes in Catalysts by Microwave Methods

  • Gerhard Fischerauer
  • Andreas Gollwitzer
  • Alexander Nerowski
  • Matthias Spörl
  • Sebastian Reiß
  • Ralf Moos


Many electrochemical reactions occur at high temperatures and inside bulk materials. Because of the difficulties associated with a direct observation of the reaction, one often resorts to indirect measurement strategies. An example is the three-way catalyst (TWC) in the exhaust pipe of a gasoline engine which stores oxygen when it is abundant in the exhaust gas and releases it later to oxidize noxious gas components such as CO in oxygen-deficient (“lean”) exhaust gases. Currently, the oxygen loading of the TWC is derived indirectly from the output signals of two lambda probes, one upstream and the other downstream of the catalyst, which monitor the air-to-fuel ratio λ in the exhaust gas. We have investigated a microwave cavity perturbation approach towards the direct measurement of the catalyst state. It will be shown that the uptake or release of oxygen in the catalyst is observable in situ via the S-parameters of a cavity resonator.


Cavity Resonator Exhaust Pipe Perfect Electric Conductor Transverse Magnetic Mode Transverse Electric Mode 
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This work was supported by the German Research Foundation (DFG), grants number Fi 956/3–1 and Mo 1060/6–1. The authors are indebted to Drs. Ulrich Göbel, Jürgen Gieshoff, and Martin Rösch from Umicore, Hanau, Germany who provided TWC samples.


  1. 1.
    C. Zimmermann, Neuartiger Sensor zur Bestimmung des Zustandes eines NOx-Speicherkatalysators (Ph.D. thesis, in German). Shaker, Aachen 2007Google Scholar
  2. 2.
    HM. Altschuler Dielectric constant. in Handbook of Microwave Measurements, vol. II, 3rd edn ed. by M. Sucher, J. Fox (Polytech. Inst. Brooklyn, Brooklyn 1963), pp. 495–548Google Scholar
  3. 3.
    SH. Chao, Measurements of microwave conductivity and dielectric constant by the cavity perturbation method and their errors IEEE Trans. MTT 33, 519–526 (1985)Google Scholar
  4. 4.
    R. Moos, M. Spörl, G. Hagen, A. Gollwitzer, M. Wedemann, G. Fischerauer, TWC: lambda control and OBD without lambda probe – an initial approach. SAE Technical Paper Series No. 2008–01–0916 (2008)Google Scholar
  5. 5.
    G. Fischerauer, M. Spörl, A. Gollwitzer, M. Wedemann, R. Moos, Catalyst state observation via the perturbation of a microwave cavity resonator. Frequenz 62, 180–184 (2008)CrossRefGoogle Scholar
  6. 6.
    G. Fischerauer, A. Gollwitzer, A. Nerowski, M. Spörl, R. Moos, On the inverse problem associated with the observation of electrochemical processes by the RF cavity perturbation method. in Proceedings of SSD’09, Djerba (2009)Google Scholar
  7. 7.
    P.S. Neelakanta, Handbook of Electromagetic Materials (CRC Press, Boca Raton, 1995)Google Scholar
  8. 8.
    G. Roussy, J.M. Thiebaut, F. Ename-Obiang, E. Marchal, Microwave broadband permittivity measurement with a multimode helical resonator for studying catalysts. Meas. Sci. Technol. 12, 542–547 (2001)CrossRefGoogle Scholar
  9. 9.
    H.L. Tuller , A.S. Nowick, Defect structure and electrical properties of nonstoichiometric CeO2 single crystals. J. Electrochem. Soc. 126, 209–217 (1979)CrossRefGoogle Scholar
  10. 10.
    P. Jasinski, T. Suzuki, H.U. Anderson, Nanocrystalline undoped ceria oxygen sensor. Sens Actuators B bf 95, 73–77 (2003)CrossRefGoogle Scholar
  11. 11.
    R.F. Harrington, Time-Harmonic Electromagetic Fields (McGraw-Hill, New York, 1961)Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  • Gerhard Fischerauer
    • 1
  • Andreas Gollwitzer
    • 2
  • Alexander Nerowski
    • 3
  • Matthias Spörl
    • 4
  • Sebastian Reiß
  • Ralf Moos
  1. 1.Bayreuth Engine Research Center (BERC), Faculty of Engineering ScienceUniversity of BayreuthBayreuthGermany
  2. 2.University of Applied Sciences FurtwangenFurtwangen im SchwarzwaldGermany
  3. 3.Technical University of DresdenFurtwangen im SchwarzwaldGermany
  4. 4.BayreuthGermany

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