Preparation, characterization and testing of Cr/AlSBA-15 ethylene polymerization catalysts
Ethylene polymerization catalysts have been prepared by grafting chromium (III) acetylacetonate onto SBA-15 (Si/Al = ¿, 156, 86 and 30) mesoporous materials. Aluminium incorporation favoured chromium anchorage onto SBA-15 surface as chromate and dichromate. The reduction temperature, determined by hydrogen TPR, decreased with the Si/Al ratio. Attachment of Cr species onto AlSBA-15 surface resulted from the interaction of hydroxyl groups with the acetylacetonate ligands through H-bonds, while a ligand exchange reaction may occur over siliceous SBA-15. The polymerization catalyst corresponding to AlSBA-15 (Si/Al = 30) support is almost four times more active than a conventional Cr/SiO2 Phillips catalyst. However, very poor polymerization activity was obtained with chromium supported on aluminium free SBA-15 material. Polymers obtained with all catalysts showed melting temperatures, bulk densities and high load melt indexes indicating the formation of linear high-density polyethylene.
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