EUROISMAR 2019

In Ti-based Ziegler-Natta catalysts (ZNCs), disagreements exist concerning which lateral surface of the MgCl$_2$ 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 TiCl$_4$ adsorbed onto the surface of MgCl$_2$ by $^{47,49}$Ti 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 TiCl$_4$/MgCl$_2$ 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 $^{49}$Ti were obtained via DFT calculations for model molecules of TiCl$_4$, 2TiCl$_4$, and Ti$_2$Cl$_8$ adsorbed onto the (110), (104), and (104)-step defect surfaces of MgCl$_2$. By comparing the obtained NMR parameters, the $^{47,49}$Ti NMR spectrum of the milled sample was assigned to TiCl$_4$ adsorbed onto the (104) surface of MgCl$_2$, which may not be a principal component of adsorption.