DRIFTS study of the interaction of the AlEt3 cocatalyst with the internal donor ethyl benzoate in supported Ziegler–Natta catalysts

The interaction of AlEt3 cocatalyst with the internal donor (ethyl benzoate–EB) in the supported Ziegler–Natta (TiCl4/EB/MgCl2) catalysts and the EB/MgCl2 support was studied by DRIFT spectroscopy. For EB/MgCl2 samples, it was shown that AlEt3 firstly removed the more weak surface complexes of EB from the MgCl2 surface and competed with EB at adsorbtion for releasing sites of the MgCl2 surface. EB, as the external donor, keeps constant the initial content and distribution of surface complexes of EB at the interaction of the AlEt3/EB mixture with the EB/MgCl2 support. At the interaction of AlEt3 with the TiCl4/EB/MgCl2 catalysts one type of surface complexes of EB is mainly removed. A part of removed EB adsorbs again on the catalyst surface in the form of complexes with aluminum-containing compounds. At the interaction of the catalyst with the AlEt3/EB mixture the EB content in the catalyst changes slightly, but the distribution of different surface complexes of EB in the catalyst changes noticeably compared to that in the initial catalyst. EB, as the external donor, adsorbs both on surface MgCl2 sites released at the removal of the internal donor and on aluminum-containing compounds adsorbed on the catalyst surface.

The internal donors in supported Ziegler–Natta catalysts form several types of complexes on surface of MgCl2 support. A part of the internal donors is removed from the catalysts at interaction of the catalysts with AlEt3 cocatalyst. IR spectroscopy of diffuse reflection (DRIFTS) was used to study the interaction of the support EB/MgCl2 and the catalysts TiCl4/EB/MgCl2 (where EB—ethyl benzoate) with AlEt3 cocatalyst. Figure optionsDownload as PowerPoint slideDRIFT spectra of the EB adsorbed on the surface of MgCl2 support (before (A) and after (B) interaction with AlEt3) demonstrating effect of AlEt3 on the distribution of EB complexes on MgCl2 surface.