Abstract
Ziegler–Natta polymerization catalysts were characterized by a complex of surface- and bulk-sensitive methods (DRIFTS, XPS, ESR, and XAS = XANES + EXAFS). A diffuse-reflectance Fourier-transform IR spectroscopy (DRIFTS) study showed the presence of strong Lewis acid sites in different concentrations and absence of strong basic sites in the polymerization catalysts. X-ray photoelectron spectroscopy (XPS), electron-spin resonance (ESR), and (X-ray absorption near-edge structure (XANES) analysis revealed the presence of Ti4+, Ti3+, Ti2+, and Ti1+ species in the surface layers and in the bulk of catalysts. The samples under study differ drastically in terms of the number of ESR-visible paramagnetic sites. The EXAFS study shows the presence of a Cl atom as a nearest neighbor of the absorbing Ti atom.
Highlights
Solid olefin polymerization catalysts represent a very important class of materials
The authors investigated the interaction between the Ethyl benzoate (EB)/TiCl4 /MgCl2 catalyst and an AlR3 co-catalyst with the goal of finding a relationship between the degree of titanium reduction and the activity in the olefin polymerization reaction
Somewhat weaker Lewis acid sites are present in the B and C catalysts, with the corresponding shifts being equal to 49–50 cm−1
Summary
Solid olefin polymerization catalysts represent a very important class of materials. Information about the nature of active sites and spectroscopic information about the Ziegler–Natta polymerization catalysts are scarce. A model Ziegler–Natta catalyst on a Pd(111) substrate coated with the MgCl2 (001) layer was prepared in an ultra-high vacuum and studied using the electron-spin resonance (ESR) technique from the point of view of the formation of radical species during the ethylene polymerization process [4]. The use of high-resolution electron microscopy in the investigation of the ethylene polymerization catalysts allowed the authors to discriminate the α-TiCl3 phase, which was destroyed rapidly after exposure to ambient air It should be noted, in view of our further discussion, that such a phase would not reveal any Ti3+ paramagnetic centers visible in ESR. The authors investigated the interaction between the EB/TiCl4 /MgCl2 catalyst and an AlR3 co-catalyst with the goal of finding a relationship between the degree of titanium reduction and the activity in the olefin polymerization reaction. This paper, wewe present details of of characterization of the Ziegler–Natta polymerization catalysts by a complex of surfaceand characterization of the Ziegler–Natta polymerization catalysts by a complex of surface- and bulkbulk-sensitive methods (DRIFTS, XPS, XAS)
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