EXAFS study of supported TiCl₄/MgCl₂ catalyst

Abstract

Extended X-ray absorption fine structure analysis (EXAFS) has been used to study supported TiCl,/MgCI, catalysts containing 1.8 wt.-% Ti. Adsorbed TiCI, was found to exist on the MgC12 surface as a dimeric complex. The possible structures of dimeric TiC14 complexes on the (100) face of MgCl, are discussed.

Coadsorption model for first-principle description of roles of donors in heterogeneous Ziegler–Natta propylene polymerization

“…Though tetravalent species also has a high activity for propylene polymerization as in group IV metallocene catalysts, TiCl 4 , which is usually situated in an octahedral symmetry on MgCl 2 [31][32][33]64], might be difficult to offer a vacant site for monomer coordination. Here, isobutyl (iBu) or methyl (Me) was employed as the alkyl group, that is, as the growing chain.…”

“…In analogous to the first-and second-generation TiCl 3 catalysts [29,30], the mononuclear species on the (1 1 0) surface and the dinuclear species on the (1 0 0) surface were respectively assigned as aspecific and isospecific active sites [25]. Although the nuclearity of surface TiCl 4 species has not been experimentally concluded yet [31][32][33], most of DFT studies have agreed on the energetic preference of the TiCl 4 mononuclear species on the (1 1 0) surface [34][35][36][37][38][39].…”

Propylene Polymerization Performance of Isolated and Aggregated Ti Species Studied Using a Well‐Designed TiCl3/MgCl2 Ziegler‐Natta Model Catalyst

“…TiCl 4 adsorbs on the MgCl 2 (110) surface only as saturated mononuclear species, while it can dimerize on the (100) surface. [4][5][6][7] Busico et al proposed that such dinuclear species was highly isospecific and mononuclear species was aspecific. [8] iii) Time-dependent change of active sites during polymerization.…”

Reductive Formation of Isospecific Ti Dinuclear Species on a MgCl2 (110) Surface in Heterogeneous Ziegler‐Natta Catalysts

“…An extended X-ray adsorption fine structure (EXAFS) analysis for a TiCl 4 /MgCl 2 precatalyst indicated the dinuclear species on the (100) surface, [6] while a recent Raman spectroscopic study on a co-milled TiCl 4 /MgCl 2 pre-catalyst suggested the mononuclear species on the (110) surface. [7] First-principle calculations showed a consistent trend, i.e.. preference of the TiCl 4 mononuclear species on the (110) surface, and that of the TiCl 4 dinuclear species on the (100) surface, which was as stable as the mononuclear species on the same surface, but absolutely less stable than the mononuclear species on the (110) surface.…”