| Autor: |
Song, W., Nicholas, J. B., Haw, J. F. |
| Zdroj: |
The Journal of Physical Chemistry - Part B; May 2001, Vol. 105 Issue: 19 p4317-4323, 7p |
| Abstrakt: |
In situ 13C NMR with both CAVERN and pulse−quench methods was used to understand the chemistry of acetone on the silico-aluminophosphate catalyst HSAPO-34. The isotropic shift of [2-13C]acetone shows that most of the acid sites on this catalyst are weaker than those on aluminosilicate zeolites, but a minority site was resolved with a shift higher than that on zeolite HZSM-5. At elevated temperatures, acetone dimerized to diacetone alcohol and dehydrated to mesityl oxide. Mesityl oxide cracked in the presence of water to acetic acid and isobutylene. Trimerization of butenes formed a significant amount of a persistent carbenium ion with unusual spectroscopic properties, and this is proposed to be the heptamethylcyclopentenyl cation, the first observation of a persistent carbenium ion on a SAPO catalyst. Chemical shift calculations at the GIAO-MP2 level revealed a discrepancy for one signal of the proposed cation but ruled out an alternative assignment. Methylaromatic formation coincided with cyclopentenyl cation synthesis, supporting a mechanistic proposal for aromatic synthesis on zeolites. Conventional flow reactor studies revealed a high selectivity for C4 olefins and rapid deactivation with acetone as feed. The results of this investigation are interpreted in the context of methanol-to-olefin (MTO) chemistry on HSAPO-34. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
|
