Oxidation behavior of ferrous cations during ion exchange into zeolites under atmospheric conditions

• Published in: Microporous and mesoporous materials Vol. 84; no. 1; pp. 302 - 317
• Main Authors: Weidenthaler, Claudia, Zibrowius, Bodo, Schimanke, Julia, Mao, Yachun, Mienert, Bernd, Bill, Eckhard, Schmidt, Wolfgang
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 15-09-2005; Elsevier
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Ion exchange; MAS NMR; Mössbauer spectroscopy; Porous materials; Surface physical chemistry; XPS; XRD; Zeolite A, X, Y; Zeolites: preparations and properties; Zeolite A, X, Y; XPS; XRD; Ion exchange; MAS NMR; Mössbauer spectroscopy; Cation exchange; Atmospheric condition; X ray; Moessbauer spectrometry; NMR spectrometry; Zeolite; X ray diffraction; Molecular sieve; Ion exchange; Zeolite A; Y; MAS NMR; Mössbauer spectroscopy; XPS; XRD; X; Photoelectron spectrometry; Oxidation
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2005.04.022

During ion exchange under atmospheric conditions, zeolites A, X, and Y facilitate the oxidation of Fe
2+ to Fe
3+ to very different extents, ranging from complete oxidation of the ferrous cations to ferric species to almost complete preservation of the ferrous state. Drying the exchanged zeolites at elevated temperature favors the oxidation reaction. The chemical environments of the low-silica zeolites A and X seem to promote the oxidation reaction more strongly than that of the more siliceous zeolite Y. Iron-rich surface layers are formed on the external surface of the zeolite particles, resulting in an apparent over-exchange especially for the low-silica zeolites. The structural integrity of the zeolite samples is differently affected by the exchange in the weakly acidic exchange solutions. The observed structural damage ranges from an almost unaffected framework, as observed for zeolite Y after one exchange, to structural collapse, as observed for zeolite X after repeated exchanges.