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Heterogenisation of zirconocene catalysts for ethylene polymerisation

Heterogenisation of zirconocene catalysts for ethylene polymerisation
Heterogenisation of zirconocene catalysts for ethylene polymerisation

A study of amorphous silica gel supported showed a decrease in the silanols content from 5.7 to 2.4 molecules per nm2 for an increase in the calcination temperature from 200 to 800oC. Infrared spectroscopy characterised different silanols types: at 200oC, isolated and H-bonded silanols were present on the surface while at 800oC only isolated silanols remained.

Supported Cp2ZrCl2 and Cp2ZrMe2 have given identical Zr K-edge EXAFS models where the zirconium centre was supported via two oxygens at 2.1 Å. The carbons of the Cp ligands remained present at 2.5 Å. Direct Si-Me bondings were present with a resonance at δ-0.1 in 1H MAS NMR. Gas titration following the deposition of Cp2ZrMe2 showed that 2 methane molecules were evolved per zirconium. No gas was evolved for Cp2ZrCl2. EDE and in situ mass spectroscopy indicated that Cp ligands desorption under N2 arose at 300oC for Cp2ZrCl2 and 450oC for Cp2ZrMe2 but carbon residues remained on silica. The difference in decomposition temperatures was suggested to be due to HCl presence in the supported Cp2ZrCl2. The decomposed samples gave an orthorhombic ZrO2Zr K-edge EXAFS model.

According to gas titration, the GaMe3 and AlMe3 were supported via evolution of 2, 1 and 0.33 of methane molecules respectively for ratios of 1/3, 1 and 3 Ga/Al per silanol available. The gas production was independent of the silica calcination temperature. Direct Si-Me, Si-OMe interactions were also observed by CP-MAS 13C NMR with resonances at δ-1 and δ 50 and Ga K-edge EXAFS indicated a 4 co-ordinated Ga centre by light scatterers, oxygen or carbon. A 1:1 ratio in silica calcined at 800oC produced monocoverage of the silica surface by GaMe3 and AlMe3. Their decomposition under N2 showed a two-stage process: a first evolution of methane corresponded to the loss of gallium co-ordinated methyls while the slower second stage represented the decomposition of adsorbed hydrocarbonaceous species. In the decomposed samples, some carbon residues remained for both Al and Ga derivatives. The gallium centre was oxygen co-ordinated gallium aggregation on the surface. For 3:1 ratios, the aggregation observed was larger (Ga co-ordination of 1.5).

Finally, Cp2ZrCl2 and GaMe3/AlMe3 were supported. Models derived from Ga and Zr K-edge EXAFS, production of methane, HCl presence, Si-Me and Si-OMe bondings were all similar to previous results. Decompositions under nitrogen were not clean and proceeded via a two-stage process for methane evolution and 1 broad process for Cp ligand decomposition. Differences were observed as 2 types of Cp ligands were characterised by 13C CP-MAS NMR in the supported samples: 1 corresponding to the Cp2ZrCl2 supported via 2 oxygens and the other representing the presence of Zr-Me interaction witnessed by 13C CP-MAS NMR with a resonance at δ 32. This model was predominant for supported Cp2ZrCl2/AlMe3 samples and its Zr K-edge EXAFS indicated no oxygen shell at 2.1 Å.

University of Southampton
Turin, Sandra
6691348e-e3e2-4afb-8384-131a363a07d0
Turin, Sandra
6691348e-e3e2-4afb-8384-131a363a07d0

Turin, Sandra (2001) Heterogenisation of zirconocene catalysts for ethylene polymerisation. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

A study of amorphous silica gel supported showed a decrease in the silanols content from 5.7 to 2.4 molecules per nm2 for an increase in the calcination temperature from 200 to 800oC. Infrared spectroscopy characterised different silanols types: at 200oC, isolated and H-bonded silanols were present on the surface while at 800oC only isolated silanols remained.

Supported Cp2ZrCl2 and Cp2ZrMe2 have given identical Zr K-edge EXAFS models where the zirconium centre was supported via two oxygens at 2.1 Å. The carbons of the Cp ligands remained present at 2.5 Å. Direct Si-Me bondings were present with a resonance at δ-0.1 in 1H MAS NMR. Gas titration following the deposition of Cp2ZrMe2 showed that 2 methane molecules were evolved per zirconium. No gas was evolved for Cp2ZrCl2. EDE and in situ mass spectroscopy indicated that Cp ligands desorption under N2 arose at 300oC for Cp2ZrCl2 and 450oC for Cp2ZrMe2 but carbon residues remained on silica. The difference in decomposition temperatures was suggested to be due to HCl presence in the supported Cp2ZrCl2. The decomposed samples gave an orthorhombic ZrO2Zr K-edge EXAFS model.

According to gas titration, the GaMe3 and AlMe3 were supported via evolution of 2, 1 and 0.33 of methane molecules respectively for ratios of 1/3, 1 and 3 Ga/Al per silanol available. The gas production was independent of the silica calcination temperature. Direct Si-Me, Si-OMe interactions were also observed by CP-MAS 13C NMR with resonances at δ-1 and δ 50 and Ga K-edge EXAFS indicated a 4 co-ordinated Ga centre by light scatterers, oxygen or carbon. A 1:1 ratio in silica calcined at 800oC produced monocoverage of the silica surface by GaMe3 and AlMe3. Their decomposition under N2 showed a two-stage process: a first evolution of methane corresponded to the loss of gallium co-ordinated methyls while the slower second stage represented the decomposition of adsorbed hydrocarbonaceous species. In the decomposed samples, some carbon residues remained for both Al and Ga derivatives. The gallium centre was oxygen co-ordinated gallium aggregation on the surface. For 3:1 ratios, the aggregation observed was larger (Ga co-ordination of 1.5).

Finally, Cp2ZrCl2 and GaMe3/AlMe3 were supported. Models derived from Ga and Zr K-edge EXAFS, production of methane, HCl presence, Si-Me and Si-OMe bondings were all similar to previous results. Decompositions under nitrogen were not clean and proceeded via a two-stage process for methane evolution and 1 broad process for Cp ligand decomposition. Differences were observed as 2 types of Cp ligands were characterised by 13C CP-MAS NMR in the supported samples: 1 corresponding to the Cp2ZrCl2 supported via 2 oxygens and the other representing the presence of Zr-Me interaction witnessed by 13C CP-MAS NMR with a resonance at δ 32. This model was predominant for supported Cp2ZrCl2/AlMe3 samples and its Zr K-edge EXAFS indicated no oxygen shell at 2.1 Å.

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Published date: 2001

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Local EPrints ID: 464691
URI: http://eprints.soton.ac.uk/id/eprint/464691
PURE UUID: 15335e6e-88fe-4973-998f-c9088cc26d00

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Date deposited: 04 Jul 2022 23:57
Last modified: 16 Mar 2024 19:42

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Author: Sandra Turin

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