Silica-magnesium-titanium Ziegler-Natta catalysts. Part 1: Structure of the pre-catalyst at a molecular level

Silica-Magnesium-Titanium Ziegler-Natta Catalysts. Part Ii. Properties of the Active Sites and Fragmentation Behaviour

“…The ZN precatalyst material was provided by SABIC and synthetized according to the procedure described in patent by Pullukat and Hoff [5], and summarized in Part 1 of this work [8]. The precatalyst was activated prior each measurement according to the following procedure: inside the glovebox a weighted amount of powder was first impregnated with anhydrous hexane (to completely fill the pores), and then with diluted aluminium alkyl, attaining the desired Al/Ti stoichiometry.…”

“…The catalyst, activated with different amounts of TEAl in the glovebox was diluted in dehydrated boron nitride (BN) and pressed in the form of a pellet, sealed inside a low-density polyethylene (LDPE) envelope under vacuum, and finally transferred in the measurement chamber at the beamline without exposure to air. Details on the settings of the beamline, data acquisition and related data processing have been reported in Part 1 of this work [8].…”

“…For investigating ethylene polymerization, small ethylene pulses were added to the He flow, as already described in our previous work [23]. Further details about the settings of the beamline, data acquisition and related data processing have been reported in Part 1 of this work [8].…”

“…The present paper focuses on a particular type of silicasupported ZN catalyst, obtained by reacting together a chemically dehydroxylated silica with a solution of an organomagnesium compounds and TiCl 4 in the presence of 1-butanol as modifier [5]. In Part 1 of this work [8], by synergistically coupling a series of advanced physicochemical methods, we have been able to disclose the molecular structure of the precatalyst. In particular, we found that two Ti phases co-exist: a Ti(III) phase with electronic properties similar to those of the b-TiCl 3 polymorph, but highly dispersed, and monomeric 6-fold coordinated Ti(IV) sites, mostly surrounded by chlorine ligands, but possibly also by some butoxide moieties.…”

Well-Defined Ti Surface Sites in Ziegler–Natta Pre-Catalysts from 47/49Ti Solid-State Nuclear Magnetic Resonance Spectroscopy

“…Thus, structural investigations based on XRD or other techniques that rely on long-range order are limited. While optical spectroscopy (IR, UV–vis, and Raman), XAS techniques and various multinuclear NMR ( 1 H, 13 C, 25 Mg, and 35 Cl) − methods have been used to address the structure of Ti sites on MgCl 2 , the results have been difficult to interpret and lead to rather poor molecular-level understanding. Furthermore, previous studies have also shown that the internal donors such as THF or ethanol, which are known to help the activation of MgCl 2 , are non-innocent and react with TiCl 4 , thus forming surface Ti alkoxo species, , that can explain the broad range of reactivity of surface sites.…”