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N. М. Gul’tsevа, Т. М. Ushakova, V. G. Krashennikov, I. N. Meshkova, F. S. D’yachkovskii


Character of active centres in supported vanadium catalysts for ethylene polymerization


Polimery 1989, No 6-7, 247


DOI: dx.doi.org/10.14314/polimery.1989.247


Summary

To investigate the possibility of enhancing, the activity of supported vanadium catalysts, the reactions of their components [VOCl3, VCl4, VO(OEt)3] as well as of the organoaluminium compounds, al-R, with the inorganic and organometallic [R2Al(OAlR)mOAlR2] oxide-type supports have been studied. The process of active centres formation has been investigated and the effect of the type of suport on the catalytic characteristics of vanadium-containing systems determined. In the reaction with a vanadium compound and with al-R take part functional groups of the support and water adsorbed physically on its surface, whereas water incorporated in the support structure romains inactive. During deposition of VOCl3 on oxide-type supports various surface vanadium compounds are formed (see formulas I—III in the text) in dependence on the concentration, distribution and type of hydroxyl groups and on the reaction temperature. The results of elementary analysis and IR-spectroscopy have revealed that the reaction of al-R with functional groups and water of the support in a medium of hydrocarbon and electrondonating solvents leads to the formation of alkylaluminoxanes which take part in the formation of active centres of polymerization (in the reactions of alkylation and reduction of vanadium compounds). The studies of ethylene polymerization with the systems of support/VOCl3 — al-R and support/al-R — VOCl3 have demonstrated that this second system has the highest catalytic activity; in this second system being present both active centres bound with the support and free active centres. In contradiction to this system, both the activity and the stability of the first-system catalyst (support/VOCl3 — al-R) depend on the chemical character of the support.


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