High resolution transmission electron microscope observation of industrial high performance Ziegler catalysts

Abstract

High resolution transmission electron microscopy (HRTEM) was used to directly observe the distribution of crystalline regions in Ziegler catalysts prepared by mechanical plus chemical routes (internal donor; Cat‐A: ethylbenzoate, Cat‐B: dibutylphthalate, Cat‐C: none) and by an entirely chemical route (internal donor; Cat‐D: dibutylphthalate). A comparison of Cat‐A, Cat‐B, and their precursors (ground products of an original MgCl2 with a donor) indicates that MgCl2 crystals are significantly destroyed by the co‐grinding procedure regardless of the kinds of internal donor, and further destruction preferentially occurs in Cat‐B compared with that in Cat‐A. The crystalline lattice of the original MgCl2 is destroyed from the surface into the interior region in the catalysts prepared by the former method. The destruction of the crystals is found to be severe in the following order: Cat‐C ≥ Cat‐B > Cat‐A in the surface area, Cat‐C > Cat‐B > Cat‐A in the central area. On the other hand, Cat‐D shows the different distribution of crystalline regions, which are predominantly present in the near‐surface area, but absent in the central area. These results suggest that the distribution of MgCl2 crystalline regions exhibit a strong correlation with the catalyst preparation procedures and, hence, the catalyst performance.

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

“…Therefore, an accurate manipulation of the initial MgCl 2 Á nLB adducts, of suitable initial stoichiometry, plays a research papers key role in the formation of nanoporous -MgCl 2 crystals, through the formation of intermediate chain-like (MgCl 2 ) x amorphous species with a three-dimensional network structure in equilibrium with the active form of MgCl 2 . The presence of these nanopores explains the experimental observation that the apparent size and shape of -MgCl 2 crystals seems to be scarcely affected by the peculiar processing conditions used for the preparation of the catalysts active in Ziegler-Natta polymerization of stereoregular olefins starting from Lewis base adducts (Mori et al, 2000). The most important microscopic parameter which is affected by the processing conditions is the concentration of magnesium sites available for the coordination of active species, which, in turn, depends on the size, concentration and distribution of nanopores (Albizzati et al, 2005).…”

“…The formation of these disordered species has a strong influence on the morphology of -MgCl 2 in terms of degree of porosity and pore size distribution. The fine control of pore size distribution and degree of porosity of the catalyst precursor, in turn, plays a key role in the industrial process of olefin polymerization with controlled morphology (Moore, 1998;Albizzati et al, 2005;Mori et al, 2000;Knoke et al, 2003;Jang et al, 2005;Ferrari et al, 2006, Fink, 2004Galli & Vecellio, 2004).…”

Discovering Hidden Material Properties of MgCl2 at Atomic Resolution with Structured Temporal Electron Illumination of Picosecond Time Resolution

“…Of note, Ziegler–Natta catalysts, which are composed of titanium active sites supported on magnesium chloride, produce a significant fraction of the world's polyethylene . Due to the acute sensitivity of the MgCl 2 to both ambient conditions and electron irradiation, electron microscopy has not fully characterized the pristine atomic and defect structure of Ziegler–Natta catalyst supports . Moreover, previous works have paid little respect to the impact of electron dose on the observed atomic structure of MgCl 2 , despite the fact that the beam‐sensitivity of MgCl 2 has been known.…”

“…Moreover, previous works have paid little respect to the impact of electron dose on the observed atomic structure of MgCl 2 , despite the fact that the beam‐sensitivity of MgCl 2 has been known. In some publications, α‐MgCl 2 is reported, while in others β‐MgCl 2 is observed . Established methods to minimize radiation damage are to restrict the accumulated electron dose below ≈20 eÅ −2 as practiced in cryomicroscopy or to use a high accelerating voltage .…”

Theoretical investigation on the model active site for isotactic polypropylene in heterogeneous Ziegler–Natta catalyst: A density functional study

“…In preparation of MgCl 2 -supported ZN catalytic system, the milling process produces different lateral surfaces of MgCl 2 on which TiCl 4 can coordinate in several ways, resulting in the formation of various active sites which differ in stereoselectivity [3][4][5]. A number of experimental studies have been performed to investigate the nature of the active sites for improving stereoselectivity of this catalyst .…”