Reduction of Cr(VI) polymerization catalysts by non-olefinic hydrocarbons

The Phillips Cr(VI)/silica catalyst, which is widely used for commercial ethylene polymerization, is usually considered to be reduced to a lower-valent active Cr species in the reactor upon contact with ethylene or other α-olefin monomers. In this paper, however, the case is presented that Cr(VI) is actually quite reactive with other hydrocarbons to which it is also often exposed, including alkanes and aromatics. Redox products from these reactions are identified, and the effect on catalyst polymerization activity and polymer character is described.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (217 K)Download as PowerPoint slideHighlights► Normally Cr(VI)/silica catalysts are reduced by alkenes to form the lower-valent active species. ► Cr(VI) catalysts can also be reduced by alkanes during storage, to produce ketones and alcohols. ► Reduction of Cr(VI)/silica by alkanes lowers the activity and melt index.