MgCl2 crystallites

Examining milled and unmilled materials, Sergeev41 found effects due to an increase of the EB concentration on pure MgCl2 crystallites (decreasing size) and on the new compound (increasing size) (Fig. 16). When EB/MgQ2 = 1.0 (molar ratio), no free MgCl2 was observable. 

An analysis of the calculated unit cell dimensions during desorption shows the lattice contracts as ammonia is removed. Since the macroscopic shape is retained, this is possible only if voids or a porosity develops simultaneously. In a macroscopic system, the salt is polycrystalline and the desorption process can be followed using, e.g. small-angle X-ray scattering (SAXS), which reveals the gradual formation of a skeletal structure (Fig. 19.9b) and the ultimate creation of an intrinsic nano-scale porosity in the MgCl2 crystallites... 

Commercially available anhydrous MgCl2 and ball-milled (with ethyl benzoate) MgCl2 crystallites are shown in Fig. 7. 

FIG. 9 (a) Surface structure and sites of hexagonal MgCl2 crystallites (two-dimensional). (Permission from Harwood Academic Publishers.) (From Ref 2.). (b) Schematic drawings of the unitary subcells and structural layers of violet TiCls and MgCl2. The bonds of the metal atoms belonging to the lateral cuts are also drawn to point out the different coordination numbers, (c) Carbonyl regions in the infrared absorption spectra of catalyst treated with ethyl benzoate. (From Harwood Academic Publishers.) (From Ref. 2.)... 

Oxidative catalysis over metal oxides yields mainly HC1 and C02. Catalysts such as V203 and Cr203 have been used with some success.49 50 In recent years, nanoscale MgO and CaO prepared by a modified aerogel/hypercritical drying procedure (abbreviated as AP-CaO) and AP-MgO, were found to be superior to conventionally prepared (henceforth denoted as CP) CP-CaO, CP-MgO, and commercial CaO/MgO catalysts for the dehydrochlorination of several toxic chlorinated substances.51 52 The interaction of 1-chlorobutane with nanocrystalline MgO at 200 to 350°C results in both stoichiometric and catalytic dehydrochlorination of 1-chlorobutane to isomers of butene and simultaneous topochemical conversion of MgO to MgCl2.53-55 The crystallite sizes in these nanoscale materials are of the order of nanometers ( 4 nm). These oxides are efficient due to the presence of high concentration of low coordinated sites, structural defects on their surface, and high-specific-surface area. 

The interest in the dimers is double. Dimerisation is a first model for the surface of the solids, increasing the coordination of the atoms without changing the oxidation states. Dimers placed on support (epitactically on the lateral surfaces of MgCl2 crystals or on the comers or edges of crystallites) have also supposed to be the reactive sites for the Ziegler-Natta reaction [40, 41]. 

Fig. 16. Dependence of the crystallite size of MgClj (curves 1, 3) and of the new compound (curves 2, 4) on the mole ratio EB/MgCl2 (1, 2) unmilled samples (3, 4) milled samples 4,). By permission of Hiithig Wepf Verlag...

The function of the internal donor in MgCl2-supported catalysts is twofold. One function is to stabilize small primary crystallites of magnesium chloride the other is to control the amount and distribution of TiCU in the final catalyst. Activated magnesium chloride has a disordered structure comprising very small lamellae. Giannini (32) has indicated that, on preferential lateral cleavage surfaces, the magnesium atoms are coordinated with four or five chlorine atoms, as... 

The commercial catalysts are heterogeneous in the sense that the active centers are on crystallites of TiCb supported on MgCl2. 

WAXD WAXD measurement was carried out with a Shimadzu X-ray diffractometer VD-2 using a scintillation counter and a pulse height analyzer. Ni-flltered CuKa radiation was used. The crystallite size of MgCl2 was calculated from the line breadth of the diffraction peaks, (003) at 2 -15.0 and (110) at 50.1 lines. 

Due to discovery of these, the onerous step of polymer deashing is no longer necessary. These compounds have to be used in combination with a triether aluminum. They have large surface area, small crystallite size, and disordered crystal structure. Due to this many Mg ions, coordinatively unsaturated, become available. On these sites TiCU can be easily adsorbed and interact. MgCl2 and TiCU undergo solid solution due to a similarity of their layer lattice structure and ionic radii. This greatly increases catalytic activity electron donation by Mg to active Ti species promotes the polymerization propagation rate constant. 

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