Supported metallocenes using inorganic–organic hybrid xerogels

Abstract

Four metallocene catalysts were prepared using two indenyl-containing aerogels as supports, treated under different conditions (triethylaluminum (TEA), methylaluminoxane (MAO) and butyllithium). The catalysts were characterized by complementary spectroscopic techniques: ultraviolet–visible spectroscopy (UV–Vis), X-ray photoelectronic spectroscopy (XPS), matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The highest metal content (1.32 mmol Zr/g-cat.) was achieved in the case of xerogel treated with TEA prior to metallocene synthesis. After MAO leaching, such content is reduced to 0.82 mmol-Zr/g-cat., exhibiting the highest activity in ethylene polymerization among the four developed catalysts. A relationship between catalyst activity and binding energy of Zr 3d 5/2 core level could be evidenced. The most active catalyst system showed a better Zr distribution, being the catalyst grain covered by aluminum cocatalyst. Depth profile monitoring by XPS measurements showed that, in fact, MAO leaches the zirconocene low binding energy species, being deposited in the uttermost surface of the grains.