MCM-41 heterogenised titanium silsesquioxane epoxidation catalysts: a spectroscopic investigation of the adsorption characteristics

Abstract

This paper describes a spectroscopic study of the heterogenisation of a novel liquid-phase epoxidation catalyst, a titanium(IV) silsesquioxane complex. Its immobilisation is performed exclusively via a straightforward adsorption of the homogeneous catalyst, i.e. the metal complex, in the pores of an MCM-41 host material. Applying all-silica MCM-41 hosts, stable and heterogeneous liquid-phase epoxidation catalysts are obtained. These highly active catalytic materials were extensively characterised using diffuse reflectance UV-Vis, XPS and Raman spectroscopy. With these techniques the strong adsorption of the intact catalytic complex within an all-silica MCM-41 host is demonstrated. A spectroscopic investigation on the ancillary cyclohexyl ligands of the silsesquioxane complex reveals strong interactions upon adsorption inside the MCM-41 pore. The interaction of these cyclohexyl ligands with the MCM-41 pore wall, as shown by Raman spectroscopy, reveals a constrained configuration of these ligands. Moreover, a hardly affected cyclopentadienyl ligand on the titanium site upon adsorption suggests a preferable orientation in which the catalytic active titanium site is pointing inside the MCM-41 pore. As such, the accessibility of the titanium site for substrate and oxidant in heterogeneous epoxidation catalysis is guaranteed, in agreement with the high catalytic activity found for these heterogeneous catalysts.

References

1. (a) T. Maschmeyer, F. Rey, G. Sankar and J. M. Thomas, Nature, 1995, 378, 159; (b) A. Corma, A. Fuerte, M. Iglesias and F. Sánchez, J. Mol. Catal. A, 1996, 107, 225; (c) J. F. Díaz, K. J. Balkus, F. Bedioui, V. Kurshev and L. Kevan, Chem. Mater., 1997, 9, 61.
2. (a) D. Avnir, Acc. Chem. Res., 1995, 28, 328; (b) Y. Shvo, Y. Becker and M. Gal, J. Chem. Soc., Chem. Commun., 1994, 2719; (c) D. Avnir, S. Braun, O. Lev and M. Ottolenghi, Chem. Mater., 1994, 6, 1605.
3. (a) P. E. F. Neys, I. F. J. Vankelecom, R. F. Parton, W. Dehean, G. L'Abbé and P. A. Jacobs, J. Mol. Catal. A, 1997, 126, L9; (b) R. F. Parton, I. F. J. Vankelcom, D. Tas, K. M. B. Janssen, P. P. Knops-Gerrits and P. A. Jacobs, J. Mol. Catal. A, 1996, 113, 283.
4. (a) K. J. Balkus, Jr., A. K. Khanmamedova, K. M. Dixon and F. Bedioui, Appl. Catal. A, 1996, 143, 159; (b) D. E. de Vos, F. Thibault-Starzyk, P. P. Knops-Gerrits, R. F. Parton and P. A. Jacobs, Macromol. Symp., 1994, 80, 157.
5. (a) J. P. Arhancet, M. E. Davis, J. S. Merola and B. E. Hanson, Nature, 1989, 339, 454; (b) J. Arhancet, M. E. Davis, J. S. Merola and B. E. Hanson, J. Catal., 1990, 121, 327; (c) K. T. Wan and M. E. Davis, Nature, 1994, 370, 449; (d) M. J. Naughton and R. S. Drago, J. Catal., 1995, 155, 383.
6. (a) T. Maschmeyer, M. C. Klunduk, C. M. Martin, D. S. Sherpard, J. M. Thomas and B. F. G. Johnson, Chem. Commun., 1997, 1874; (b) M. Crocker, R. H. Herold and A. G. Orpen, Chem. Commun., 1997, 241; (c) K. Wada, M. Nakashitoa, A. Yamamoto and T. Mitsudo, Chem. Commun., 1998, 133; (d) for a recent review see: H. C. L. Abbenhuis, Chem. Eur. J., in the press.
7. (a) F. J. Feher, T. A. Budzichowski, K. Rahimian and J. W. Ziller, J. Am. Chem. Soc., 1992, 114, 3859; (b) I. E. Buys, T. W. Hambley, D. J. Houlton, T. Maschmeyer, A. F. Masters and A. K. Smith, J. Mol. Catal., 1994, 86, 309.
8. S. Krijnen, H. C. L. Abbenhuis, R. W. J. M. Hanssen, J. H. C. van Hooff and R. A. van Santen, Angew. Chem. Int. Ed. Engl., 1997, 37, 356.
9. H. C. L. Abbenhuis, S. Krijnen and R. A. Van Santen, J. Chem. Soc., Chem. Commun., 1997, 331.
10. 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. Higgens and J. L. Schlenker, J. Am. Chem. Soc., 1992, 114, 10834.
11. M. Busio, J. Jänchen and J. H. C. Van Hooff, Microporous Mater., 1995, 5, 211.
12. J. H. Scofield, J. Electron Spectrosc. Relat. Phenom., 1976, 8, 129.
13. S. Krijnen, H. C. L. Abbenhuis, R. W. J. M. Hanssen, J. H. C. van Hoof and R. A. van Santen, Proc. Mater. Research Soc., in the press.
14. H. C. L. Abbenhuis, M. L. W. Vorstenbosch and A. L. Spek, unpublished results.
15. J. Kärger, M. Petzold, H. Pfeifer, S. Ernst and J. Weitkamp, J. Catal., 1992, 136, 283.
16. L. Frunza, H. Kosslick, H. Landmesser, E. Höft and R. Fricke, J. Mol. Catal. A, Chem., 1997, 123, 179.
17. C. L. Angell, J. Phys. Chem., 1973, 77, 222.
18. C. Brémard, J. Laureyns and J. Patarin, J. Raman Spectrosc., 1996, 27, 439.
19. A. Davidson, S. J. Weigel, L. M. Bull and A. K. Cheetham, J. Phys. Chem. B, 1997, 101, 3065.
20. P. K. Dutta, B. Del Barco and D. C. Shieh, Chem. Phys. Lett., 1986, 127, 200.