Abstract
The Phillips Cr/silica polymerization catalyst has been examined by means of X-ray photoelectron spectroscopy and chemical methods, and the results have been compared to activity measurements from a high-pressure autoclave. Only Cr(VI) was found after O 2 at 600–800 °C, but CO at 350 °C cleanly reduced this to Cr(II). On contact with ethylene, which increased the binding energy slightly, the divalent material became an active polymerization catalyst. Reducing Cr(VI) with ethylene produced similar results. This indicates Cr(II) as the active precursor and that its electron density is decreased by the ethylene.
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