Abstract
Abstract The IR spectra of the modified chromocene/Co/silica gel catalyst show a band at 3118 cm" 1 of the cyclopentadienyl ligand, which is shifted by -1-20 cm' 1 compared to the unmodified chromocene/silica gel catalyst. The comparably slow CO adsorption yields two bands at low Cr concentration (-0.1% Cr) at 2065 and 2022 cm" 1 and two more at higher Cr concentration (-1% Cr) at 2028 and 1961 cm -1 . Both band pairs are significantly different from that observed with the "normal" chromocene/silica gel catalyst at 2046 and 1974 cm -1 . No CO IR bands at low wavenumbers were observed with the modified catalyst. Polymerisation measurements showed a slightly lower concentration of catalytically active sites (35% of Cr) for the modified catalyst compared to the unmodified one (50%), while the poly-merisation activity decreased by a factor of four (Cr concentration: 0.083%). It was concluded that the surrounding of the dimeric surface site is changed by Co on the silica gel surface of the chromocen catalyst and that this change is important for the CO adsorption and the polymerisation activity.
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