Effect of a Lewis Acid additive on active sites formation in zirconocene catalyst systems: A DFT study

BELELLI, PATRICIA GABRIELA; DANIEL EDUARDO, DAMIANI; CASTELLANI, NORBERTO JORGE

JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL

Elsevier

Año: 2004 vol. 208 p. 147 - 158

1381-1169

Comparative theoretical analysis of optimized geometries and electronic structures of Cp2ZrCl2/methylaluminoxane (MAO) system and its interactions with a third component was performed. The additive studied was a Lewis acid compound: AlCl3. Density functional theory (DFT), that included exchange and correlation effects, was employed with Gaussian basis sets. Additive enhances the cocatalyst Lewis acid character and, indirectly, it modifies the electrophilicity of Zr atom. By comparing the geometrical structure and charge distribution of the site with and without AlCl3 it is possible to understand the reasons of polymerization performance improvement. Previous experimental results for these systems have showed a notable increase in ethylene and propylene polymerization activity.2ZrCl2/methylaluminoxane (MAO) system and its interactions with a third component was performed. The additive studied was a Lewis acid compound: AlCl3. Density functional theory (DFT), that included exchange and correlation effects, was employed with Gaussian basis sets. Additive enhances the cocatalyst Lewis acid character and, indirectly, it modifies the electrophilicity of Zr atom. By comparing the geometrical structure and charge distribution of the site with and without AlCl3 it is possible to understand the reasons of polymerization performance improvement. Previous experimental results for these systems have showed a notable increase in ethylene and propylene polymerization activity.