MgCl₂‐supported Ziegler‐Natta catalysts: A DFT‐D ‘flexible‐cluster’ approach. TiCl₄ and probe donor adducts

Abstract

In this paper we introduce a DFT‐D ‘flexible‐cluster’ approach to the computational modeling of MgCl2‐supported Ziegler‐Natta catalysts. The adsorption of TiCl4 and probe donor molecules on plain and defective lateral terminations of monolayered MgCl2 clusters was studied allowing for full structure relaxation by means of modern DFT methods including dispersion corrections. The approach offers a good compromise between speed and accuracy, and has great potential for realistic simulations of the catalytic species in industrially relevant formulations. In particular, compared with periodic DFT‐D descriptions, it is better able to capture the features of real nano‐sized and highly disordered primary catalyst particles with complex adsorbate compositions.

Probing Interactions between Electron Donors and the Support in MgCl2-Supported Ziegler–Natta Catalysts

“…The presented periodic calculations have some conceptual problems, as the small MgCl 2 nanoparticles lack long-range crystalline order. In ref ( 56 ), an alternative cluster description has been presented that should be better suited to describe such disordered systems. On the basis of this cluster approach, we proposed some high-coverage models 34 that were indeed found to better describe the MgCl 2 –DMDOMe adducts as far as 13 C chemical shifts of the donor are concerned.…”

“…At lower loadings, the resulting Mg sites will be pentacoordinated. Alternatively, TiCl 4 molecules might coordinate on steps or holes 9 , 56 with structures locally resembling the structural motive, as shown in Figure 6 , so that for at least one of the two magnesium sites octahedral coordination is restored. C Q for the octahedral magnesium sites comes down to approximately 2 MHz, which is very close to the bulk value.…”

Structural Characterization of Electron Donors in Ziegler–Natta Catalysts

“…The structural models behind the latter calculations have been presented independently elsewhere. 38 , 39…”

Disclosing the Interaction between Carbon Monoxide and Alkylated Ti3+ Species: a Direct Insight into Ziegler–Natta Catalysis

“…This was taken as an indication that the strongly acidic Mg 2+ sites are no more available for CO adsorption because they are selectively occupied by chemisorbed TiCl x species, 17 in agreement with recent theoretical calculations. 37 − 41 …”