Abstract
Zeolites are highly important heterogeneous catalysts. Besides BrOnsted
SiOHAl acid sites, also framework Al-FR Lewis acid sites are often found
in their H-forms. The formation of Al-FR Lewis sites in zeolites is a
key issue regarding their selectivity in acid-catalyzed reactions. The
local structures of Al-FR Lewis sites in dehydrated zeolites and their
precursorsperturbed Al-FR atoms in hydrated zeoliteswere studied by
high-resolution MAS NMR and FTIR spectroscopy and DFT/MM calculations.
Perturbed framework Al atoms correspond to (SiO)(3)AlOH groups and are
characterized by a broad Al-27 NMR resonance ((i)=59-62ppm, C-Q=5MHz,
and =0.3-0.4) with a shoulder at 40ppm in the (27)AlMASNMR spectrum.
Dehydroxylation of (SiO)(3)AlOH occurs at mild temperatures and leads to
the formation of Al-FR Lewis sites tricoordinated to the zeolite
framework. Al atoms of these (SiO)(3)Al Lewis sites exhibit an extremely
broad (AlNMR)-Al-27 resonance ((i)approximate to 67ppm, C-Q approximate
to 20MHz, and approximate to 0.1).
Original language | English |
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Pages (from-to) | 541-545 |
Number of pages | 5 |
Journal | Angewandte Chemie (International Edition) |
Volume | 54 |
Issue number | 2 |
DOIs | |
Publication status | Published - 07 Jan 2015 |
Fields of science
- 104 Chemistry
- 104021 Structural chemistry
- 104015 Organic chemistry
- 104017 Physical chemistry
- 106041 Structural biology
- 301305 Medical chemistry
- 302043 Magnetic resonance imaging (MRI)
JKU Focus areas
- Nano-, Bio- and Polymer-Systems: From Structure to Function
- Engineering and Natural Sciences (in general)