The Phillips catalyst, which contains chromium dispersed on silica, accounts for 40 � 50 % of global high density polyethylene (PE) production. The active catalytic sites of the Phillips catalyst remains unknown, though X-ray Absorption Spectroscopy shows that Cr(II) species are formed, inferring that they are responsible for catalysis. We grafted [Cr(OSi(OtBu)3)2]2 and thermally removed the organic ligands to generate well-defined silica supported dimeric Cr(II) species, which are converted into Cr(III) silicates by treatment with N2O according to XAS and model molecular studies. While the Cr(II) species is hardly active in ethylene polymerization, the Cr(III) species exhibits activities exceeding those of the Phillips catalyst, though the PE produced by these two materials is very similar in terms of molecular weight and dispersity indicating similar active sites.  The mononuclear Cr(III) analogues can be prepared from [Cr(OSi(OtBu)3)3] via the same approach, and it also displays high activity in the polymerization of ethylene.  These results lay the foundation to design new supported Cr(III) ethylene polymerization catalysts

Well-defined chromium silicates as efficient ethylene polymerization catalysts in the absence of co-catalyst: A clue in the Phillips catalyst

247th National Meeting (2014)

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