Microporous and mesoporous supports and their effect on the performance of supported metallocene catalysts

详细信息    查看全文

• 作者：Fern ; o Silveira ; Maria do Carmo Martins Alves ; Fern ; a C. Stedile ; Sibele B. Pergher ; Joã ; o Henrique Zimnoch dos Santos
• 关键词：Supported metallocene ; Polyethylene ; Microporous supports ; Mesoporous supports ; EXAFS
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2010
• 出版时间：15 January 2010
• 年：2010
• 卷：315
• 期：2
• 页码：213-220
• 全文大小：1053 K

文摘

A series of hybrid-supported catalysts was prepared by sequentially grafting Cp₂ZrCl₂ and (nBuCp)₂ZrCl₂ (1:3 ratio) onto synthesized silica–zirconia xerogel, alumino-silicates, alumina, chrysotile and commercial MAO (methylaluminoxane)-modified silica. Supported catalysts were characterized by Rutherford backscattering spectrometry, atomic force microscopy, extended X-ray absorption fine structure spectroscopy, X-ray diffraction and nitrogen adsorption. The grafted metal content was between 0.21 and 1.00 wt. % Zr/SiO₂ or Zr/Al₂O₃. All of the systems were shown to be active in ethylene polymerization with methylaluminoxane as the cocatalyst. The catalyst activity and polymer molecular weight depended on the effects of the textural characteristics of the supports on the structure of the generated supported catalyst species. The highest activity in ethylene polymerization (ca. 6560 kgPE molZr⁻¹ h⁻¹) was reached with the supported catalyst using commercial MAO-modified silica and also presented the lowest surface roughness. Correlation between EXAFS data and polymer characteristics was extracted: the production of polyethylenes with higher molecular weight was associated with the reduction in the interatomic Zr–O distance of the supported catalysts, which was shown to be dependent on the nature of the support.