Structural Characterization of the EtOH–TiCl₄–MgCl₂ Ziegler–Natta Precatalyst

The Ziegler–Natta polymerization is one major example of application of catalysis in industry. Since the first discovery of Ziegler and Natta, several modifications of the catalyst have been developed, in order to improve its performance. Nowadays, a typical Ziegler–Natta catalyst for polyethylene synthesis consists of a precatalyst, composed of TiCl₄ supported on MgCl₂ in the presence of a Lewis base, activated by organoaluminum. The atomic-scale characterization of the Ziegler–Natta catalyst is crucial for further improvement of the catalyst. Here, the precatalyst TiCl₄–MgCl₂ with EtOH as internal Lewis base is characterized combining solid-state NMR spectroscopy and periodic density functional theory calculations. From total energy and NMR spectra, eight surface species were proposed showing EtO^– ligands on the Ti and EtOH/EtO^– on the surface Mg species. These species lead to a complete interpretation of the NMR two-dimensional spectra. Hence a detailed molecular scale description of the precatalyst was obtained