Issue 15, 2000
From the journal:

Physical Chemistry Chemical Physics

Surface acidity modifications induced by thermal treatments and acid leaching on microcrystalline H-BEA zeolite. A FTIR, XRD and MAS-NMR study

Marcella Trombetta,a   Guido Busca,*a   Loretta Storaro,b   Maurizio Lenarda,b   Manuela Casagrandeb  and  Alfonso Zambonc  

* Corresponding authors

a Dipartimento di Ingegneria Chimica e di Processo “G. Bonino”, Uniersità, P.le J.F. Kennedy, Genoa, Italy
E-mail: icibusca@csita.unige.it;
Fax: 0039-010-3536028
Tel: 0039-010-3536024

b Dipartimento di Chimica, Uniersità di Venezia Ca' Foscari, Dorsoduro, Venezia, Italy

c Dipartimento di Scienze Ambientali, Uniersità di Venezia Ca' Foscari, Dorsoduro, Venezia, Italy

Abstract

Samples of beta-zeolite thermally treated at different 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-methoxy-naphthalene. It has been shown that the as prepared sample presents two types of extraframework species. These are identified 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 effect. The Brønsted acid sites present in the sinusoidal channels (νOH=3608 cm−1) can be distinguished from those located in the larger ones (νOH=3620–3612 cm−1), due to the inability of the bulky probe molecule pivalonitrile to enter the former. However, internal terminal silanols (νOH=3735 cm−1) also apparently display a significant Brønsted acidity, definitely higher than the acidity of those absorbing at 3747 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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Article information

DOI
https://doi.org/10.1039/B001916J
Article type
Paper
Submitted
09 Mar 2000
Accepted
05 Jun 2000
First published
11 Jul 2000

Phys. Chem. Chem. Phys., 2000,2, 3529-3537

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Surface acidity modifications induced by thermal treatments and acid leaching on microcrystalline H-BEA zeolite. A FTIR, XRD and MAS-NMR study

M. Trombetta, G. Busca, L. Storaro, M. Lenarda, M. Casagrande and A. Zambon, Phys. Chem. Chem. Phys., 2000, 2, 3529 DOI: 10.1039/B001916J

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