Structure and reducibility of a Fe/Al sub(2)O sub(3) catalyst for selective catalytic reduction studied by Fe K-edge XAFS spectroscopy

• Published in: Journal of physics. Conference series 2013-01, Vol.430, p.1-4
• Main Authors: Boubnov, A, Lichtenberg, H, Mangold, S, Grunwaldt, J-D
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Ammonia; Catalysts; Clusters; Distortion; Electronics; Selective catalytic reduction; Zeolites
• ISSN: 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/430/1/012054

EXAFS and pre-edge information from the Fe K-edge absorption spectra is used in this study to characterise the local environment and geometry of Fe-centres in a 1% Fe/Al sub(2)O sub(3) model catalyst. The EXAFS results reveal clusters of 2-3 Fe oxo-moieties dispersed on the Al sub(2)O sub(3)-support. The Fe super(3+) centres are coordinated by 6 O-atoms in a strongly distorted octahedral geometry. This is supported by the pre-edge peak, which is far more intense than in [alpha]-Fe sub(2)O sub(3) absorption data acquired for comparison. For preliminary investigations, catalytic tests for selective catalytic reduction (SCR) of NO sub(x) by ammonia and in situ XANES studies of Fe/Al sub(2)O sub(3) are compared with previously published data for Fe/zeolite systems. The low SCR activity of Fe/Al sub(2)O sub(3) (compared to Fe/zeolite catalysts) in which the Fe super(3+) species do not change their electronic state under SCR-relevant conditions (reference temperature 250[degrees]C in our case) correlates well to the significantly higher temperatures required to reduce these species to Fe super(2+). The difference in reducibility (and consequently in the SCR-activity) between the two systems probably results from differences in the structure and the electronic interaction of the Fe oxomoieties and the particular catalyst support.