Inelastic Neutron Scattering Investigation of MgCl₂Nanoparticle-Based Ziegler-Natta Catalysts for Olefin Polymerization

The effect of nanosize and structural disorder on the MgCl2 support of Ziegler-Natta catalysts has been investigated in terms of induced changes to their vibrational spectroscopic fingerprint. In particular, the inelastic neutron scattering (INS) technique was used, which allowed sampling of the whole lattice dynamics of the support. The experimental INS spectra of several ball-milled, polycrystalline, samples of MgCl2 were collected for the first time and were compared to simulated spectra from quantum-mechanical density functional theory calculations. Theoretical calculations were performed on a variety of MgCl2 structural models: (i) ordered and disordered bulk (3D); (ii) low-dimensional structures such as surfaces (2D) and nanorods (1D); and nanoclusters (0D). This allowed us to link specific features of the spectra to specific changes in the atomic structure and dynamics of the catalyst support. In particular, the effect of translational symmetry breaking and rotational disorder is discussed. Furthermore, the present data suggest that the ball-milling process mostly leads to the formation of bulk-like crystallites rather than nanoparticles. This work ultimately highlights the combined use of INS measurements and quantum-mechanical simulations as an effective approach for the atomistic characterization of defective (nano)materials.