Phillips Trivalent

The Phillips Cr/silica polymerization catalyst is prepared by impregnating a chromium compound onto a wide pore silica and then calcining in oxygen to activate the catalyst. This leaves the chromium in the hexavalent state, monodispersed on the silica surface. Chromium trioxide (Cr03) has been impregnated mast commonly, but even a trivalent chromium salt can be used since oxidation to Cr(VI) occurs during calcining. 

Scheme 3 Plausible structures of surface-stabilized trivalent chromium species Cr(III)Ojj jurf on the silica surface of the Phillips Cr/silica catalyst...

Activation of the Phillips catalyst directly by ethylene monomer was further investigated by XPS and TPD-MS methods in order to shed some light on the reaction mechanisms during the induction period. Deconvolution of the XPS spectra for industrial Phillips Cr/silica catalysts treated in ethylene atmosphere at RT for 2 h revealed that surface chromium species presented in three oxidatimi states surface chromate Cr(Vl)0 c,surf species surface-stabilized trivalent Cr(III) species and surface-stabilized Cr(II) species. Compared to the original catalyst before ethylene treatment, about one-third of chromate Cr(VIX) c,surf species (i.e., ca. 22.6% of the whole surface Cr) was reduced to Cr species in lower oxidation states during the ethylene treatment, even under ambient conditions [67]. 

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