| Autor: |
Josef Dadok, Gordon J. Kennedy, R. S. Ozubko, A.S. Chesnick, J.D. Graham, G. C. Gobbi, W. J. Murphy, Aksel A. Bothner-By, Colin A. Fyfe |
| Rok vydání: |
1985 |
| Předmět: |
|
| Zdroj: |
Zeolites. 5:179-183 |
| ISSN: |
0144-2449 |
| DOI: |
10.1016/0144-2449(85)90027-2 |
| Popis: |
The 29Si MAS n.m.r. spectra of highly dealuminated zeolites are shown to exhibit separate Si(OAl) resonances due to crystallographically inequivalent lattice sites. The chemical shift dispersion due to crystallographic inequivalence is of the same order of magnitude as that from the presence of aluminium atoms in the first coordination sphere and can result in the overlapping of resonances. Thus, the interpretation of the 29Si MAS n.m.r. spectra of zeolites of low Si Al ratios can be ambiguous. The correct peak assignments are presented for the zeolites offretite and omega and the problems involved in obtaining quantitatively reliable Si Al ratios from the spectra discussed. In the case of offretite it is not possible to completely describe the distribution of silicon and aluminium over its two non-equivalent crystallographic sites, although the Si Al ratios for a number of samples are shown to agree with a random distribution. For zeolite omega it is possible to completely describe the non random Si distribution and to predict the aluminium distribution, which is in excellent agreement with that obtained independently from the high field (14.1T) 27Al MAS n.m.r. spectrum. All data indicate that Si and Al distributions in omega are not random in nature. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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