A theoretical investigation of the binding of TiCln to MgCl2

The structure of the (0 0 0 1) surface of the alpha -MgCl2 crystal has been investigated using DFT-GGA periodic calculations. The calculated surface r elaxation is in agreement with LEED measurements. Motivated for the use of MgCl2 as support for the Ziegler-Natta reaction, we have studied the adsorp tion of the catalyst (titanium chlorides as monomers or dimers) on the (1 0 0) and (1 1 0) MgCl2 surfaces. The structures of adsorbed species are clos e to those previously found on cluster models: bridging chlorine atoms conn ect the Ti to the Mg atoms and the systems remain in high spin states. The (0 0 0 1) surface is the most stable face of the alpha -MgCl2 crystal; howe ver it is Cl-terminated and henceforth poorly reactive; it had been suggest ed to deposit metallic Mg in order to improve its reactivity. Our modelling explains the failure of this tentative; the interaction between the deposi ted metal and the surface is repulsive and uncharged Mg atom does not bind. (C) 2001 Elsevier Science B.V. All rights reserved.