IR Characterization of Homogeneously Mixed Silica–Alumina Samples and Dealuminated Y Zeolites by Using Pyridine, CO, and Propene Probe Molecules

Homogeneously mixed silica–alumina samples with various Si/Al ratios (Si/Al = 9/1, 7/3, 5/5, 3/7, and 1/9) were prepared and characterized by infrared spectroscopy. Pyridine, propene, and CO were used as probe molecules to detect Brønsted and Lewis acid sites. The homogeneity of Si and Al in mixed o...

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Veröffentlicht in:Journal of physical chemistry. C 2013-07, Vol.117 (27), p.14043-14050
Hauptverfasser: Matsunaga, Yuichi, Yamazaki, Hiroshi, Yokoi, Toshiyuki, Tatsumi, Takashi, Kondo, Junko N
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Sprache:eng
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Zusammenfassung:Homogeneously mixed silica–alumina samples with various Si/Al ratios (Si/Al = 9/1, 7/3, 5/5, 3/7, and 1/9) were prepared and characterized by infrared spectroscopy. Pyridine, propene, and CO were used as probe molecules to detect Brønsted and Lewis acid sites. The homogeneity of Si and Al in mixed oxides was confirmed by comparison with a physical mixture of pure silica and alumina. The continuous change of spectral appeared by increasing or decreasing the Si/Al ratio in silica–alumina samples. The frequency of the broad band due to surface OH groups hydrogen-bonded to CO was found to be a measure of the Si/Al ratio in silica–alumina samples roughly. This information was used to characterize steam-treated HY and NH4Y zeolites. Dealumination from the framework structure and generation of extra-framework silica–alumina were apparent for both steam-treated zeolites, which were not identified by X-ray diffraction patterns and microscope images. The Si/Al ratios of the formed silica–alumina on steam-treated YH and NH4Y zeolites were roughly estimated to be 5/5 and 7/3, respectively, by the peak position of hydrogen-bonded OH bands when CO was adsorbed. The acid strength of both steam-treated samples was weakened, and it was more apparent for HY than NH4Y zeolite.
ISSN:1932-7447
1932-7455
DOI:10.1021/jp403242n