On the crystal structure and cation valence of Mn in Mn-substituted Ba-{beta}-Al{sub 2}O{sub 3}
- Politecnico di Milano, Milan (Italy)
- Univ. di Milano, Milan (Italy). Dipt. di Scienza della Terra
BaMn{sub x}Al{sub 12{minus}x}O{sub 19{minus}{alpha}} combustion catalysts with x = 0.5, 1.0, 2.0, 3.0 have been investigated. The crystal structure and, specifically, the partitioning and the dominant oxidation state of Mn in the different crystallographic sites has been clarified by means of X-ray absorption spectroscopy and X-ray powder diffraction structure refinements of multiple diffraction powder data sets collected with both synchrotron and Cu-K{alpha} radiation at different wave lengths in proximity and far from the Mn K adsorption edge. The results show that at low loading (up to x = 1) Mn preferentially enters tetrahedral Al(2) sites of Ba-{beta}{sub I}-Al{sub 2}O{sub 3} as divalent cation. The occupancy of Ba sites in the mirror planes acts as a charge compensation mechanism to balance substitution of Al{sup 3+} with Mn{sup 2+}. At high Mn loading (x {ge} 1) the occupation of Ba sites reaches unity and Mn preferentially enters octahedral Al(1) sites as Mn{sup 3+}. Surface area measurements and catalytic activity tests in CH{sub 4} combustion have also been performed. The results indicate that the incorporation of Mn in the octahedral Al(1) sites causes reduction of surface area and has no beneficial effect on catalytic activity.
- OSTI ID:
- 289429
- Journal Information:
- Journal of Catalysis, Vol. 179, Issue 2; Other Information: DN: Paper presented at the 3. international world conference on catalytic combustion, September 23--25, 1996, Amsterdam (NL); PBD: 25 Oct 1998
- Country of Publication:
- United States
- Language:
- English
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