ISSN:
0749-1581
Keywords:
tert-Butyl alcohol
;
Dehydration
;
H-ZSM-5 zeolite
;
2H NMR
;
Molecular mobility
;
Diffusion
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The molecular mobility and dehydration reaction of tert-butyl alcohol, selectively deuteriated in the methyl groups (t-BuOH[2 - 2H9], dTBA), absorbed on H-ZSM-5 zeolite was studied using 2H NMR spectroscopy. At 173-298 K two modes of fast anisotropic motion were observed for the adsorbed alcohol: rotation of CD3 groups around the C—C bonds and rotation of the entire (CD3)3C fragment around the C—O bond. The influence of the walls of the H-ZSM-5 channels on the geometry of adsorbed dTBA is small, the increase in the CD3—C—O 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 2H NMR lineshape and two types of butene oligomers: less mobile species with the lineshape typical of solid-state 2H NMR and more mobile species with a liquid-like lineshape. The number of more mobile species increases with increase in temperature. In addition, 2H 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 m2 s-1 at 373 K, whereas for oligomers with a solid-like lineshape D ≪ 5 × 10-14 m2 s-1 at 173-373 K. The diffusion coefficient for the t-BuOH molecule was estimated as D ≪ 2 × 10-14 m2 s-1 within the temperature range 173-296 K.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260320105
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