Roles for Cyclopentenyl Cations in the Synthesis of Hydrocarbons from Methanol on Zeolite Catalyst HZSM-5
| Autor: | James F. Haw, Catherine S. Heneghan, John B. Nicholas, Zhike Wang, Weiguo Song, Feng Deng, and Teng Xu |
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| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | Journal of the American Chemical Society. 122:4763-4775 |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/ja994103x |
| Popis: | In situ 13C NMR measurements on samples prepared using a pulse-quench catalytic reactor show that the 1,3-dimethylcyclopentenyl carbenium ion (1) is an intermediate in the synthesis of toluene from ethylene on zeolite catalyst HZSM-5. Cation 1 forms in less than 0.5 s when ethylene is pulsed onto the catalyst bed at 623 K, and its presence obviates the kinetic induction period for conversion of a subsequent pulse of dimethyl ether, or methanol, into olefins (MTO chemistry). The kinetic induction period returns when the interval between pulses is many times the half-life of 1 in the catalyst bed. Density functional theory calculations (B3LYP/ 6-311G**) on a cluster model of the zeolite confirm that 1 is stable in the zeolite as a free cation and suggest why the alternative framework alkoxy is not observed. A π complex of the neutral cyclic diene is only 2.2 kcal/mol higher in energy than that of the ion pair. Theoretical (GIAO-MP2/tzp) 13C isotropic shifts of isolated 1 are in good agreement with the exper... |
| Databáze: | OpenAIRE |
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