Inelastic Neutron Scattering Investigation of MgCl₂ Nanoparticle-Based Ziegler–Natta Catalysts for Olefin Polymerization

Abstract

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.

Spectroscopic Fingerprints of MgCl2/TiCl4 Nanoclusters Determined by Machine Learning and DFT

“…More recently, different nanostructures were obtained in terms of disorder and morphology, which in turn influence the overall catalytic performance. The investigation was further extended by looking at the lattice dynamics of MgCl 2 systems by means of inelastic neutron scattering (INS) spectroscopy, which is a valuable method to probe the motion of atoms within a material and hence understand the structural disorder of nanosized systems. In recent years, some of the authors have sharpened the use of FT-IR spectroscopy of adsorbed carbon monoxide as a technique to get information on the MgCl 2 exposed surfaces and their relative extent. , The method, which was attempted for the very first time by Zakharov and co-workers, was demonstrated to be particularly powerful, especially when the MgCl 2 surfaces are not fully occupied by the other components and/or by side residues of the synthesis.…”

Supported Metal Nanoparticles‐Based Catalysts and their Interactions with H2: Insights from Inelastic Neutron Scattering Spectroscopy

“…One example is chlorine (total neutron scattering cross section = 16.8 barn) in the MgCl 2 support employed in the Ziegler-Natta catalysts, for which it was possible to detect the effect of the decrease in particles dimension and of the increase of disorder as a function of the ball-milling time. [9] On the other hand, INS is also extremely powerful to investigate the species formed under in situ conditions in the presence of a H-donor, among all H 2 . This is particularly valuable when investigating hydrogenation catalysts, as the methodology provides a unique perspective over the hydrogenous species active for the hydrogenation process.…”

“…Interestingly, in the last few years it was also demonstrated that the modern instrumental resolution is sufficient to investigate also non‐hydrogenous materials and to focus on other elements with a sufficiently high neutron scattering cross section. One example is chlorine (total neutron scattering cross section=16.8 barn) in the MgCl 2 support employed in the Ziegler‐Natta catalysts, for which it was possible to detect the effect of the decrease in particles dimension and of the increase of disorder as a function of the ball‐milling time [9] . On the other hand, INS is also extremely powerful to investigate the species formed under in situ conditions in the presence of a H‐donor, among all H 2 .…”

Structure–property relationship in film and blow molding type high‐density polyethylene polymers from a slurry‐process industrial plant

“…4,5 In addition, polymer characteristics such as bulk density, melt flow behavior, as well as molecular weight, and comonomer composition distribution (CCD) can significantly influence the performances of polyolefin materials. 6 However, the correlation between Ziegler-Natta catalyst structure and properties of the resulted polymers remains a great challenge. [7][8][9] Recently, the studies into the relationship between HDPE particle size/distribution and its characteristics have attracted a lot of attention.…”

“…The particle size distribution (PSD) of the used catalyst determines the products' PSD 4,5 . In addition, polymer characteristics such as bulk density, melt flow behavior, as well as molecular weight, and comonomer composition distribution (CCD) can significantly influence the performances of polyolefin materials 6 . However, the correlation between Ziegler‐Natta catalyst structure and properties of the resulted polymers remains a great challenge 7–9 …”