We have examined the ability of chromyl chloride to react with silica to yield the desired surface chromate esters that are widely believed to be the initiation site of the Phillips catalyst. CrO₂Cl₂ vapor reacts at 25 °C under reduced pressure with silica pretreated at 200, 450, and 800 °C.  Grafting proceeds by reaction with the surface silanols, as confirmed by infrared spectroscopy and formation of HCl.  The primary product of this reaction is ≡SiOCrO₂Cl, as confirmed by XAS.

The ≡SiOCrO₂Cl site does not initiate ethylene polymerization without heat treatment.  However, EXAFS shows that conversion to the dichromate ester occurs spontaneously upon thermal treatment in vacuo, both by condensation with neighboring silanol groups and co-condensation of adjacent ≡SiOCrO₂Cl sites.

Differences observed in the XAS spectra of the CrO₂Cl₂-treated silicas pretreated at different temperatures provide insight into the dependence of polymerization activity on the thermal history of the catalyst.