Saturation of Magnesium Dichloride Crystallites by Titanium Tetrachloride
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CitationZorve, Peter. Linnolahti, Mikko. (2020). Saturation of Magnesium Dichloride Crystallites by Titanium Tetrachloride. Surface science, 699, 121627. 10.1016/j.susc.2020.121627.
Magnesium dichloride and titanium tetrachloride are key components of Ziegler–Natta polymerization catalysts. We report a systematic computational study at M06-2X/def-TZVP level, thus accounting for dispersion, on saturation of magnesium dichloride crystallites by titanium tetrachloride. The crystallites are represented by (MgCl2)n clusters of various sizes and shapes, with n = 4–94, and they show preference for (104)-type edges with five-coordinate Mg atoms. Preferred adsorption modes of TiCl4 upon full saturation of crystallite edges are identified, alongside with adsorption strengths and relative stabilities of the (MgCl2)n-(TiCl4)m products. Consistent with previous literature, both Ti and Mg have tendency of favoring octahedral six-coordination, which can be achieved at all surface sites, including corners, serving as representatives of defect sites on the MgCl2 surfaces. The adsorption strengths of TiCl4 are the strongest for crystallites having (110)-type edges with four-coordinate Mg atoms. The much higher reactivity of (110)-type edges compared to (104)-type edges leads to reversal of the stability order of the crystallites upon TiCl4 adsorption. Saturated (MgCl2)n-(TiCl4)m crystallites thus favor shapes rich in (110)-type edges.