47,49Ti solid-state NMR and DFT study of Ziegler-Natta catalyst: Adsorption of TiCl4 molecule onto the surface of MgCl2

• Published in: The Journal of physics and chemistry of solids 2019-12, Vol.135, p.109088, Article 109088
• Main Authors: Iijima, Takahiro, Shimizu, Tadashi, Goto, Atsushi, Deguchi, Kenzo, Nakai, Toshihito, Ohashi, Ryutaro, Saito, Masayoshi
• Format: Article
• Language: English
• Subjects: Czjzek; DFT; Quadrupole; SSNMR; Titanium; ZNC
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/j.jpcs.2019.109088

In Ti-based Ziegler-Natta catalysts (ZNCs), disagreements exist concerning which lateral surface of the MgCl2 support adsorbs Ti species so as to be an active site for the catalysis of polymerization. In the present paper, we investigated the local structure of TiCl4 adsorbed onto the surface of MgCl2 by 47,49Ti solid-state nuclear magnetic resonance (NMR) spectra at 21.8 T along with density functional theory (DFT) calculations. The magic-angle-spinning NMR spectrum of the TiCl4/MgCl2 adduct sample prepared by 20 h of milling, which exhibited broadened and shifted peaks compared to that of the sample without milling, was simulated by a Czjzek model considering the distribution of quadrupole interaction parameters. The electric field gradient and chemical shielding tensors of 49Ti were obtained via DFT calculations for model molecules of TiCl4, 2TiCl4, and Ti2Cl8 adsorbed onto the (110), (104), and (104)-step defect surfaces of MgCl2. By comparing the obtained NMR parameters, the 47,49Ti NMR spectrum of the milled sample was assigned to TiCl4 adsorbed onto the (104) surface of MgCl2, which may not be a principal component of adsorption. [Display omitted] •47,49Ti solid state NMR spectra of Ziegler-Natta catalysts.•Spectral simulation using a Czjzek distribution model.•DFT calculations of EFG and CSA tensors for some model molecules.•Assignment of 47,49Ti peaks to TiCl4 adsorbed onto (104) of MgCl2.