Theoretical investigation of (MgCl₂)_xpolynuclear species formed during preparation of MgCl₂-supported Ziegler–Natta catalysts from solid solvates

Abstract

A novel approach for the study of the nature of the active species in Ziegler-Natta catalysis is described. This approach is based on the study of reliable structural models for disordered (MgCl 2 ) x polynuclear species which develop during the preparation of MgCl 2 -supported catalysts starting from MgCl 2 -Lewis-base adducts, and the calculation of X-ray diffraction patterns of these models. A method for the calculation of the X-ray powder diffraction patterns of the model structures is devised. This diffraction modelling method may be useful for the correct interpretation of the nature of some diffraction features in the X-ray diffraction patterns recorded during the structural evolution of MgCl 2 -Lewis-base adducts, which occurs in the preparation of the catalyst systems used for Ziegler-Natta polymerization of olefins.Both forms are characterized by typical diffraction peaks in the X-ray diffraction profiles at 2 (Cu K) ' 15 (d = 5.90 Å , 003 or 001 reflections for and forms, respectively), at 2 ' Figure 1Model of the Cl-Mg-Cl structural layer in MgCl 2 layer compounds showing the (100) and (110) cuts. The hexagonal unit-cell parameters a = b = 3.64 Å (Dorrepaal, 1984) are also indicated.research papers

Genesis of MgCl2‐based Ziegler‐Natta Catalysts as Probed with Operando Spectroscopy

“…In this sense, the structure of the solid MgCl 2 -6MeOH adduct can be considered as an arrangement of discrete octahedra with Mg 2 + ions in the centers and MeOH molecules in the corners, and with the chloride ions excluded from the Mg 2 + coordination sphere as counterions. [62,82] The final XRPD pattern (pattern 7) is that 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 of a layered d-MgCl 2 phase characterized by an extensive structural disorder, in agreement with the literature findings, [83,84] although the sporadic alternation of only partially converted MgCl(OMe) layers cannot be excluded. In particular, the disappearance of the two peaks at 198 and 218 (triangles in Figure 2a) and the appearance of a very weak peak at 12.58 in pattern 4 (star in Figure 2a) are associated with the transition from predominantly solvated ionic structures to covalent MgCl 2 long chains, featuring chlorine bridges connecting the Mg atoms.…”

The Influence of Alcohols in Driving the Morphology of Magnesium Chloride Nanocrystals

“…In contrast, the MgCl 2 ⋅ 6 MeOH adduct loses five out of the six ligands at 150 °C, which is in agreement with the fact that the volatility of methanol is higher than that of ethanol. In both cases, a layered MgCl 2 phase characterized by extensive structural disorder is obtained, as demonstrated by the X‐ray powder diffraction (XRPD) patterns shown in Figure b and in agreement with the literature . The two diffraction patterns are very similar, irrespective of the starting precursor.…”

“…In both cases, al ayered MgCl 2 phase characterized by extensive structural disorder is obtained, as demonstrated by the X-ray powderd iffraction (XRPD) patterns shown in Figure 1b and in agreement with the literature. [55,[57][58][59][60] The two diffraction patterns are very similar,i rrespectiveoft he starting precursor.This is ac lear limit of the XRPD technique, which is unable to reveal subtle structural differences for nanosizeda nd disordered materials.…”

Crystal Structures of Ziegler–Natta Catalyst Supports

“…In fact, until now, all the computer simulations have been based on the oversimplification of assuming the insertion of TiCl 4 species and donors over selected plain‐cut surfaces of crystalline α‐MgCl 2 4. 6m, 11 Precise knowledge of the building units and isomer configuration occurring in the structure of precursors will lead to a new approach for the modeling and design of Ziegler–Natta catalysts.…”