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Chemische Prozesse und Phasenübergänge Poster: Mi., 14:00–16:30 M-P171
2D-Mapping of the catalyst structure inside a fixed-bed reactor: Partial
oxidation of methane over a Rh/Al2O3-catalyst
Jan-Dierk Grunwaldt 1 , Stefan Hannemann 1 , Pit Boye 2 , Christian G.
Schroer 2 , Alfons Baiker 1
1 Institute for Chemical and Bioengineering, Department of Chemistry and Applied
Biosciences, ETH Zurich, Hoenggerberg, HCI, CH-8093 Zurich – 2 Department of Structural
Physics, TU Dresden, D-01062 Dresden
In situ X-ray absorption spectroscopy is a well-suited technique to gain information
on the structure of heterogeneous catalysts. In certain cases a variation of the catalyst
structure can occur inside a catalytic reactor as a result of temperature or concentration
gradients. This requires spatially resolved molecular information on a microscale.
Here, we have used a position sensitive X-ray camera to record XANES spectra from
inside the catalytic reactor with a spatial resolution on the scale of a few micrometers
[1]. The catalytic performance was determined simultaneously using mass spectrometric
analysis. Partial oxidation of methane over Rh/Al2O3 catalyst is used as
an example. For recording locally resolved the absorption of the sample inside the
catalytic microreactor, a CCD camera was installed behind the in situ cell and X-ray
absorption images were recorded around the Rh K-edge (23220 eV) as shown in the
Figure. In total, 170 absorption images were taken that allowed the reconstruction
of the full Rh K-edge XANES spectra at each pixel (a corresponding movie can be
downloaded at [2]). The measurements uncovered tremendous changes of the structure
of the Rh particles along the catalyst bed within less than 100 micrometer. The shape
and position of the gradient strongly depended on temperature and flow [3].
[1] J.-D. Grunwaldt et al., J. Phys. Chem. B 110 (2006) 8674.
[2] http://www.baiker.ethz.ch/people/Scistaff/Grunwaldt/ESI
[3] J.-D. Grunwaldt et al., in preparation.
Fig. 1: X-ray absorption
of Rh/Al2O3 inside the microreactor
at different energies
during the partial oxidation
of methane (cf. refs.
[1,2])