Deuterium solid-state NMR study of the molecular mobility and dehydration of tert-butyl alcohol on zeolite H-ZSM-5
✍ Scribed by Alexander G. Stepanov; Alexander G. Maryasov; Vyacheslav N. Romannikov; Kirill I. Zamaraev
- Publisher
- John Wiley and Sons
- Year
- 1994
- Tongue
- English
- Weight
- 721 KB
- Volume
- 32
- Category
- Article
- ISSN
- 0749-1581
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
The molecular mobility and dehydration reaction of tert‐butyl alcohol, selectively deuteriated in the methyl groups (t‐BuOH[2 – ^2^H~9~], dTBA), absorbed on H‐ZSM‐5 zeolite was studied using ^2^H NMR spectroscopy. At 173–298 K two modes of fast anisotropic motion were observed for the adsorbed alcohol: rotation of CD~3~ groups around the CC bonds and rotation of the entire (CD~3~)~3~C fragment around the CO bond. The influence of the walls of the H‐ZSM‐5 channels on the geometry of adsorbed dTBA is small, the increase in the CD~3~CO angle not exceeding 2.7 ± 1.2° compared with the same angle in solid dTBA. This is explained by location of the alcohol molecules at channel intersections of the zeolite, whose dimensions exceed those of the dTBA molecule. The lifetime of the dTBA molecule at these adsorption sites exceeds 1 × 10^−5^ s. The observed reaction products are deuteriated water with an unusual ^2^H NMR lineshape and two types of butene oligomers: less mobile species with the lineshape typical of solid‐state ^2^H NMR and more mobile species with a liquid‐like lineshape. The number of more mobile species increases with increase in temperature. In addition, ^2^H NMR indicates the presence of tert‐butyl groups in the reaction products. For oligomers with a liquid‐like lineshape, the diffusion coefficient D is 3 × 10^−13^ m^2^ s^−1^ at 373 K, whereas for oligomers with a solid‐like lineshape D ≪ 5 × 10^−14^ m^2^ s^−1^ at 173‐373 K. The diffusion coefficient for the t‐BuOH molecule was estimated as D ≪ 2 × 10^−14^ m^2^ s^−1^ within the temperature range 173–296 K.