Dynamics of benzene, cyclohexane and n-hexane in KL zeolite studied by 2H NMR

(Note: The full text of this document is currently only available in the PDF Version )

Takayuki Sato, Kimio Kunimori and Shigenobu Hayashi


Abstract

Molecular motions of benzene-d6, cyclohexane-d12 and n-hexane-d14 sorbed at loading levels of 1 molecule per channel lobe in KL zeolite have been studied by 2H NMR. The spectra were recorded in the temperature range from 124 to 373 K, and they were successfully simulated. At low temperatures, benzene molecules rotate fast around the C6 axis, and cyclohexane molecules rotate fast around the C3 axis of the chair form, where the directions of the rotation axis are fixed. With increase in temperature, benzene, cyclohexane, and n-hexane molecules start jumping among the six equivalent sites on K+ ions. Further increases in temperature results in the increase in the fraction of molecules located at the central space of the micropore which undergo isotropic motions and exchange with the molecules on the K+ ions. The mean residence time on the K+ ion is in the following order: benzene-d6>cyclohexane-d12>n-hexane-d14. The apparent activation energies derived from the mean residence times are 28.0±1.6 kJ mol-1 (220 K⩽T⩽373 K) for benzene-d6, 9.6±1.2 kJ mol-1 (160 K⩽T⩽260 K) and 44.3±3.6 kJ mol-1 (280 K⩽T⩽373 K) for cyclohexane-d12, and about 10 kJ mol-1 for n-hexane-d14. The large activation energy at the high temperatures in cyclohexane-d12 might be caused by the conformation inversion of the cyclohexane ring. The ratios of the numbers of molecules in the central space to those on the K+ ions are in the order of benzene-d6<cyclohexane-d12<n-hexane-d14. In conclusion, the interaction between the guest molecules and KL zeolite is in the following decreasing order: benzene-d6>cyclohexane-d12>n-hexane-d14.


References

  1. J. R. Bernard, in Proceedings of the Fifth International Conference on Zeolites, ed. L. V. C. Rees, Heydon, London, 1980, p. 686 Search PubMed.
  2. R. M. Barrer and H. Villiger, Z. Kristallogr., 1969, 128, 352 CAS.
  3. R. Eckman and A. J. Vega, J. Am. Chem. Soc., 1983, 105, 4841 CrossRef CAS.
  4. B. Zibrowius, J. Caro and H. Pfeifer, J. Chem. Soc., Faraday Trans. 1, 1988, 84, 2347 RSC.
  5. B. Boddenberg and R. Burmeister, Zeolites, 1988, 8, 488 CAS.
  6. I. Kustanovich, H. M. Vieth, Z. Luz and S. Vega, J. Phys. Chem., 1989, 93, 7427 CrossRef CAS.
  7. L. M. Bull, N. J. Henson, A. K. Cheetham, J. M. Newsam and S. J. Heyes, J. Phys. Chem., 1993, 97, 11776 CrossRef CAS.
  8. R. L. Portsmouth, M. J. Duer and L. F. Gladden, J. Chem. Soc., Faraday Trans., 1995, 91, 559 RSC.
  9. G. Vitale, L. M. Bull, R. E. Morris, A. K. Cheetham, B. H. Toby, C. G. Coe and J. E. MacDougall, J. Phys. Chem., 1995, 99, 16087 CrossRef CAS.
  10. L. M. Bull, A. K. Cheetham, B. M. Powell, J. A. Ripmeester and C. I. Ratcliffe, J. Am. Chem. Soc., 1995, 117, 4328 CrossRef CAS.
  11. J. A. S. Goncalves, R. L. Portsmouth, P. Alexander and L. F. Gladden, J. Phys. Chem., 1995, 99, 3317 CrossRef.
  12. S. M. Auerbach, L. M. Bull, N. J. Henson, H. I. Metiu and A. K. Cheetham, J. Phys. Chem., 1996, 100, 5923 CrossRef CAS.
  13. B. G. Silbernagel, A. R. Garcia, J. M. Newsam and R. Hulme, J. Phys. Chem., 1989, 93, 6506 CrossRef CAS.
  14. S. Hayashi, K. Hayamizu, S. Mashima, A. Suzuki, P. J. McElheny and A. Matsuda, Jpn. J. Appl. Phys., Part 1, 1991, 30, 1909 Search PubMed.
  15. M. S. Greenfield, A. D. Ronemus, R. L. Vold, R. R. Vold, P. D. Ellis and T. E. Raidy, J. Magn. Reson., 1987, 72, 89.
  16. J. C. Powell, W. D. Phillips, L. R. Melby and M. Panar, J. Chem. Phys., 1965, 43, 3442 CrossRef.
  17. N. Boden, S. M. Hanlon, Y. K. Levine and M. Mortimer, Mol. Phys., 1978, 36, 519 CAS.
  18. S. Hayashi, Clays Clay Miner., 1997, 45, 724 CrossRef CAS.
  19. S. C. Wofsy, J. S. Muenter and W. Klemperer, J. Chem. Phys., 1970, 53, 4005 CAS.
Click here to see how this site uses Cookies. View our privacy policy here.