Samples of beta-zeolite thermally treated at di†erent temperatures and acid leached with diluted hydrochloric acid solution have been investigated by XRD, 27Al MAS-NMR spectroscopy and FTIR spectroscopy. The results have been used to interpret the behaviour of the samples as catalysts for the acylation of 2-methoxynaphthalene. It has been shown that the as prepared sample presents two types of extraframework species. These are identiÐed as Al hydroxo-ions highly dispersed in the internal zeolite channels and Al oxide nanoparticles. Calcination causes dealumination of the framework and progressive conversion of the Al hydroxo-ions into Al oxide nanoparticles that reduce the zeolite channels practicability, modifying the shape selectivity e†ect. The acid sites present in the sinusoidal channels cm BrÔnsted (l ~1) can be OH \ 3608 distinguished from those located in the larger ones cm (l ~1), due to the inability of the bulky OH \ 3620È3612 probe molecule pivalonitrile to enter the former. However, internal terminal silanols cm (l ~1) also OH \ 3735 apparently display a signiÐcant acidity, deÐnitely higher than the acidity of those absorbing at 3747 BrÔnsted cm~1, thought to be located at the external crystal surface. The strongest Lewis acidity is displayed by the aluminum hydroxo-ions, while that of alumina nanoparticles is a little weaker. Acid-leached beta-zeolite also displays a medium strength Lewis acidity, likely due to framework Al cations. Thus a partial reinterpretation of the real structure of beta-zeolite and a partial reassignment of the bands due to the surface hydroxy groups are proposed.
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|Data di pubblicazione:||2000|
|Titolo:||Surface acidity modifications induced by thermal treatments and acid leaching on microcrystalline H-BEA zeolite. A FTIR, XRD and MAS-NMR study|
|Autori:||Trombetta, M. and Busca; and Storaro, G.; and Lenarda, L.; and Casagrande, M.; and Zambon, A.|
|Digital Object Identifier (DOI):||10.1039/B001916J|
|Appare nelle tipologie:||Articolo su rivista|
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