Abstract
Ziegler–Natta heterogeneous catalytic systems are extensively used to polymerize ethylene and propylene. Some industrial catalysts consist of TiCl4 chemisorbed on activated MgCl2 and subsequently reduced and alkylated by reaction with an aluminum alkyl (generally AlEt3). Lewis bases are added to the catalytic systems to control the enantio-selectivity for the production of isotactic polypropylene. Our aim is to clarify the chemical composition of the active centers by modern surface science methods. Model catalysts are prepared in the form of ultra-thin films by gas-phase deposition on a gold foil in ultrahigh vacuum. Under these conditions, MgCl2 films grow to controlled thickness via a layer-by-layer mechanism, as revealed by AES and XPS. TiCl4 can be deposited on these films near room temperature by both electron irradiation-induced and metallic magnesium-induced chemical vapor deposition. Angle-resolved XPS studies indicate that these films consist of a few layers of TiCl2 with one monolayer of TiCl4 chemisorbed on its surface. The exposure of these titanium chloride films to the co-catalyst AlEt3 produces an active model Ziegler–Natta catalyst. XPS analysis reveals the presence of TiCl2Et on the catalyst surface: this is believed to be the active site. Prolonged reaction with the co-catalyst reduces the titanium sites to TiClEtn (n = 1 and/or 2). High molecular weight polyethylene and polypropylene are synthesized on these catalysts, as shown by Raman spectroscopy. Highly isotactic polypropylene is produced without need for stereo-regulating Lewis bases.
Similar content being viewed by others
REFERENCES
J. Boor Jr., Ziegler-Natta Catalysis and Polymerization (Academic Press, New York, 1979).
S. van der Ven, Polypropylene and Other Polyolefins: Polymeriza-tion and Characterization (Elsevier, Amsterdam, 1990).
E. Albizzati, U. Giannini, G. Collina, L. Noristi and L. Resconi, in: Polypropylene Handbook, ed. E.P. Moore Jr. (Carl Hanser, Munich, 1996) ch. 2.
J.J.A. Dusseault and C.C. Hsu, J. Macromol. Sci., Rev. Macromol. Chem. Phys. C 33 (1993) 103.
G. Fink, R. M¨ulhaupt and H.H. Brintziger, eds., Ziegler Catalysis (Springer, Heidelberg, 1994).
P.C. Barb`e, G. Cecchin and L. Noristi, Adv. Polym. Sci. 81 (1986) 1.
Y.V. Kissin, Isospecific Polymerization of Olefins with Heteroge-neous Ziegler-Natta Catalysts (Springer, New York, 1985).
P. Corradini, V. Barone, R. Fusco and G. Guerra, Eur. Polym. J. 15 (1979) 133.
P. Corradini, V. Barone, R. Fusco and G. Guerra, J. Catal. 77 (1982) 32.
P. Corradini, V. Barone and G. Guerra, Macromolecules 15 (1982) 1242.
P. Corradini, V. Barone and G. Guerra, Eur. Polym. J. 20 (1984) 1177.
V. Venditto, G. Guerra, P. Corradini and R. Fusco, Eur. Polym. J. 27 (1991) 45.
P. Corradini and G. Guerra, Prog. Polym. Sci. 16 (1991) 239.
E. Magni and G.A. Somorjai, Appl. Surf. Sci. 89 (1995) 187.
E. Magni and G.A. Somorjai, Surf. Sci. 341 (1995) L1078.
E. Magni and G.A. Somorjai, Surf. Sci. 345 (1996) 1.
E. Magni and G.A. Somorjai, J. Phys. Chem. 100 (1996) 14786.
E. Magni and G.A. Somorjai, J. Phys. Chem., in press.
E. Magni and G.A. Somorjai, Surf. Sci. 377 (1997) 824.
E. Magni and G.A. Somorjai, Catal. Lett. 35 (1995) 205.
G.A. Somorjai, Introduction to Surface Chemistry and Catalysis (Wiley, New York, 1994).
D.P. Woodruff and T.A. Delchar, Modern Techniques of Surface Science (Cambridge University Press, Cambridge, 1994).
D. Briggs and M.P. Seah, Practical Surface Analysis, Vol. 1 (Wiley, Baffins Lane, Chichester, 1990).
J.L. K¨onig, Spectroscopy of Polymers (American Chemical Society, Washington, DC, 1992) (Series title: ACS professional reference book).
D.L. Bower and W.F. Maddams, The Vibrational Spectroscopy of Polymers (Cambridge University Press, New York, 1988).
D.O. Hummel, in: Polymer Spectroscopy, ed. D.O. Hummel (Chemie, Weinheim, 1974).
E. Schr¨oder, G. M¨uller and K.-F. Arndt, Polymer Characterization (Carl Hanser, M¨unchen, 1989).
P.J. Hendra and J.K. Agbenyega, The Raman Spectra of Polymers (Wiley, New York, 1993).
J.L. K¨onig, Spectrochim. Acta 22 (1966) 1223.
J.L. K¨onig, L.E. Wolfram and J.G. Grasselli, Spectrochim. Acta 22 (1966) 1233.
C.D. Bain, J. Chem. Soc. Faraday Trans. 91 (1995) 1281.
Y.R. Shen, Nature 337 (1989) 519.
Y.R. Shen, Ann. Rev. Phys. Chem. 40 (1989) 327.
P. Guyot-Sionnest and Y.R. Shen, Phys. Rev. B 35 (1987) 4420.
P. Guyot-Sionnest, J.H. Hunt and Y.R. Shen, Phys. Rev. Lett. 59 (1987) 1597.
D. Zhang, Y.R. Shen and G.A. Somorjai, Chem. Phys. Lett. 281 (1997) 394.
D.H. Fairbrother, J.G. Roberts, S. Rizzi and G.A. Somorjai, Lang-muir 13 (1997) 2090.
D.H. Fairbrother, J.G. Roberts and G.A. Somorjai, Surf. Sci. 399 (1998) 109.
J.G. Roberts, M. Gierer, D.H. Fairbrother, M.A. Van Hove and G.A. Somorjai, Surf. Sci. 399 (1998) 123.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Korányi, T.I., Magni, E. & Somorjai, G.A. Surface science approach to the preparation and characterization of model Ziegler–Natta heterogeneous polymerization catalysts. Topics in Catalysis 7, 179–185 (1999). https://doi.org/10.1023/A:1019159616214
Issue Date:
DOI: https://doi.org/10.1023/A:1019159616214