47,49Ti solid-state NMR and DFT study of Ziegler-Natta catalyst: Adsorption of TiCl4 molecule onto the surface of MgCl2
Abstract
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.
- Publication:
-
Journal of Physics and Chemistry of Solids
- Pub Date:
- December 2019
- DOI:
- 10.1016/j.jpcs.2019.109088
- Bibcode:
- 2019JPCS..13509088I
- Keywords:
-
- ZNC;
- SSNMR;
- Titanium;
- DFT;
- Quadrupole;
- Czjzek