Indenyl-silica xerogels: new materials for supporting metallocene catalysts

Inorganic–organic hybrid xerogels bearing indenyl groups on their surfaces have been synthesised by the sol–gel method. The hybrid xerogels were obtained by hydrolysis and polycondensation of bisindenyldiethoxysilane (Ind₂Si(OEt)₂) and tetraethoxysilane, TEOS (Si(OEt)₄) under two different conditions. Chemical structure was investigated by ultraviolet spectroscopy (UV–VIS), transmittance (FT-IR) and diffuse-reflectance (DRIFTS) infrared spectroscopy, magic angle spin nuclear magnetic resonance (MAS-NMR) and X-ray photoelectron spectroscopy (XPS). Xerogel texture and structure were analysed by nitrogen sorption based on the Brunauer–Emmett–Teller (BET) method, X-ray diffraction spectroscopy (XRD), and natural scanning electron microscopy (N-SEM). Under our experimental conditions, in alkaline milieu and 1:3 indenyl/TEOS ratio, a xerogel with higher indenyl content, but nonporous and showing agglomerate patterns was produced (xerogel I). Spherical particles of diameter about 6–8 μm where obtained in the absence of catalyst, using 1:5 indenyl/TEOS ratio, higher temperature and shorter reaction time (xerogel II). Xerogel II was used as support for heterogeneous metallocene catalyst synthesis. The resulting catalyst presented high Zr content (0.68 mmol Zr g_cat⁻¹) and high catalyst activity (40×10³ kg PE mol⁻¹ Zr h⁻¹) in ethylene polymerisation.