Controlling the channel diameter of the mesoporous molecular sieve MCM-41

Abstract

We describe a simple method of controlling the channel diameter of the mesoporous molecular sieve MCM-41 in the 26.1–36.5 Å range and the wall thickness in the 13.4–26.8 Å range while using the same gel mixture. This is achieved by varying the synthesis temperature in the 70–200°C range and/or reaction times in the 0.5–96 h range. The unit cell parameter, channel diameter, thickness of the channel wall, surface area, degree of polymerization and grain morphology were monitored by X-ray diffraction, N₂ adsorption, ²⁹Si magic-angle-spinning NMR and transmission electron microscopy. MCM-41 with wider and thicker-walled channels and higher degree of polymerization is prepared at higher temperatures and at longer reaction times. Thick-wall MCM-41 has higher thermal stability but lower surface area. The material with the thickest channel wall ever reported (26.8 Å) can withstand calcination at nearly 1000°C with little structural damage. We suggest a mechanism for the increase of wall thickness and channel diameter. Fascinating morphological features involving sealed silicate ‘tubes’ and ‘vesicles’ up to 1200 Å in diameter are observed.

References

1. D. W. Breck, Zeolite Molecular Sieves: Structure, Chemistry and Use, Wiley, London, 1974.
2. C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature (London), 1992, 359, 710.
3. J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. T.-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc., 1992, 114, 10834.
4. E. F. Vansant, Pore Size Engineering in Zeolites, Wiley, Chichester, 1990.
5. D. Khushalani, A. Kuperman, G. A. Ozin, K. Tanaka, J. Garces, M. M. Olken and N. Coombs, Adv. Mater., 1995, 7, 842.
6. N. Coustel, F. D. Renzo and F. Fajula, J. Chem. Soc., Chem. Commun., 1994, 967.
7. P. T. Tanev and L. T. Vlaev, J. Colloid Interface Sci., 1993, 160, 100.
8. G. Engelhardt and D. Michel, High-resolution Solid-State NMR of Silicates and Zeolites, Wiley, Chichester, 1987.
9. C.-F. Cheng, H. He, W. Zhou and J. Klinowski, Chem. Phys. Lett., 1995, 244, 117.
10. B. P. Feuston and J. B. Higgins, J. Phys. Chem., 1994, 98, 4459.
11. N. A. Mazer, G. B. Benedek and M. C. Carey, J. Phys. Chem., 1976, 80, 1075.
12. J. N. Israelachvili, Intermolecular and Surface Forces, Academic Press, London, 2nd edn., 1985.
13. H. Wenneström and F. Evans, The Colloidal Domain, VCH, New York, 1994.
14. O. Regev, S. Ezrahi, A. Azerin, E. Wachtel, N. Garti, E. W. Kaler, A. Khan and Y. Talmon, Langmuir, 1996, 12, 668.
15. B. Lindman, N. Kamenka, B. Brun and P. G. Nilsson, in Microemulsion, ed. I. D. Robb, Plenum, New York, 1982.