| Abstract
| - Tremendous changes of the structure of Rh particles occurred during partial methane oxidation to hydrogenand carbon monoxide over a 2.5 wt % Rh/Al2O3 catalyst upon ignition of the catalytic reaction. Furthermore,near the ignition temperature a variation in the Rh-valence state along the catalyst bed was observed. Bycombining hard X-ray absorption spectroscopy (X-ray absorption near edge structure, XANES) with a chargedcoupled device (CCD) camera and using a suitable spectroscopic cell with gas supply and on-line massspectrometry, we demonstrate that 2D-mapping of the Rh-oxidation state in a catalyst bed can be achievedduring the catalytic reaction. For this purpose, X-ray images were recorded with the CCD camera at eachenergy around the Rh K-edge with and without the spectroscopic cell. This resulted effectively in the transmittedand incident intensity at each energy and at each pixel of the spectroscopic cell. Reconstruction of the full RhK-edge XANES spectra at each pixel revealed the local distribution of oxidized and metallic Rh-species inthe catalyst bed. Along the catalyst bed, structural changes were found with a steep gradient within less than100 μm. Furthermore, a characteristic cone toward the inlet of the spectroscopic cell was observed.
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