Correlation of oxidation states of surface chromium species with ethylene polymerization activity for Phillips CrOx/SiO2 catalysts modified by Al-alkyl cocatalyst

Correlation of oxidation states of surface Cr species on TEA-modified Phillips catalysts with their ethylene polymerization activity in terms of catalyst calcination temperature and Al/Cr molar ratio suggested that the real active Cr precursor might be a Cr2+·2Cr6+ cluster (Scheme 1). Based on this plausible cluster model, the active sites concentration is estimated to be around 14.4-24.9 (mol% Cr) for the TEA-modified Phillips catalysts.