Ethylene polymerization over transition‐metal supported catalysts. II. Cr on zeolite, silica, and charcoal: Characterization and activity studies

Abstract

Cr catalysts supported on silica, zeolite NaY, and charcoal were prepared with two different methods. They were characterized and examined in the polymerization of ethene. Cyclic voltammetry, electron spin resonance, X‐ray photoelectron spectroscopy and silicon‐29 magic‐angle spinning nuclear magnetic resonance spectroscopy were used to characterize them, demonstrating that Cr is not in a single oxidation state, that the distribution among the various oxidation states depends on the history of the sample, and that even for a single oxidation state a variety of different environments can occur. In the polymerization of ethene, the supported Cr catalysts exhibited activity values varying from 103 to 105 gPE · molCr−1 · [M]−1 · h−1, depending on the choice of the support and on the method by which the Cr is placed on it. Silica seemed to be the most efficient support for Cr for this reaction. However, the zeolite‐supported catalysts also showed reasonable activity values (Ap ≅ 104 units) and presented the advantage of having a strong interaction between the Cr and the support, which may prevent leaching of the cation into the surrounding environment. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3768–3780, 2003

Kinetic modeling studies of ethylene polymerization reactions using supported chromium catalysts

“…The chromium/charcoal sample, prepared by the incipient wetness method with a chromium concentration of 4%, was also studied with XPS. The experimental details and a more extensive discussion of the characterization results were presented previously 1…”

“…Details on the preparation and characterization of the catalysts were reported in the second part of this set of articles 1…”

“…In the second article of this series,1 the characterization of a set of supported chromium catalysts was reported, as well as their activity in the polymerization of ethylene under various experimental conditions. In this article, studies on the kinetics of the polymerization reaction with these catalysts are reported.…”

Review of the Phillips Chromium Catalyst for Ethylene Polymerization

“…Recent FTIR evidence suggests that coordination to silanols is possible [279]. For example, catalysts can be made from amorphous aluminophosphates, γ -alumina, stoichiometric AlPO 4 and zeolites [124,218,[305][306][307]. This was attributed to a change in the Si − O − Cr − O − Si bond angle or distance, perhaps analogous to tight bridging in metallocenes.…”

“…For silicas, fragility generally requires high pore volume and most commercial silicas sold as adsorbents or zeolites or supports for other catalytic applications cannot be used for polymerization because their pore volume is too low [41,124,218,306,307,373]. For other supports this principle may or may not apply depending on its structure and inherent strength.…”