Access to Local Structures of HS-AlF3 and Its Precursor Determined by High-Resolution Solid-State NMR
| Autor: | E. Kemnitz, M. Bertmer, Gunther Brunklaus, R. König, Gudrun Scholz, C. Jäger, A. Pawlik |
|---|---|
| Rok vydání: | 2009 |
| Předmět: |
Magic angle
Chemical shift chemistry.chemical_element Surfaces Coatings and Films Electronic Optical and Magnetic Materials Amorphous solid NMR spectra database chemistry.chemical_compound Crystallography General Energy chemistry Solid-state nuclear magnetic resonance Octahedron Aluminium Physical and Theoretical Chemistry Fluoride |
| Zdroj: | The Journal of Physical Chemistry C. 113:16674-16680 |
| ISSN: | 1932-7455 1932-7447 |
| Popis: | High-surface aluminum fluoride (HS-AlF 3 ) is an interesting catalytic material and possesses high surface areas compared to crystalline aluminum fluorides and strong Lewis acidity. HS-AlF 3 and its precursor aluminum isopropoxide fluoride are X-ray amorphous, which makes precise structural elucidations very difficult, which is, in turn, the prerequisite for understanding its extraordinary properties. For this reason 27 Al NMR using magic angle sample spinning (MAS) and multiple quantum NMR (MQMAS) has been carried out at different magnetic field strengths up to 19.9 T in order to gain maximum information about the various AlF 6―x O x (x = 0, 1, 2, ...) octahedra present in the precursor and HS-AlF 3 structure. The 27 Al NMR spectra are almost featureless irrespective of the applied B o fields because of distributions of isotropic chemical shifts and second order quadrupolar effects. Nevertheless, it was possible to verify the presence of four different octahedra in the materials following the results of earlier investigations of the sol-gel of these HS-AlF 3 samples. Different oxygen-containing AlF 5 O and AlF 4 O 2 are found in the precursor structure, whereas AlF 6 sites determine the HS-AlF 3 structure besides residual AlF 5 O and AlF 4 O 2 octahedra after postfluorination of the precursor. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|