Journal
JOURNAL OF CATALYSIS
Volume 293, Issue -, Pages 1-12Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcat.2012.05.014
Keywords
Polymerization; Phillips catalyst; Chromyl chloride; Silica; X-ray absorption spectroscopy; ONIOM
Categories
Funding
- National Science Foundation [CBET08-54425]
- China Scholarship Council (CSC)
Ask authors/readers for more resources
Compositionally and structurally uniform chromate sites grafted onto silica via the ambient temperature reaction of CrO2Cl2 with silica pretreated at either 500 or 800 degrees C, followed by mild heating at 300 degrees C, were reduced by CO to the corresponding Cr(II) sites. The resulting structures were investigated by IR spectroscopy of adsorbed CO as well as X-ray absorption spectroscopy and compared with model structures predicted by ONIOM calculations (B3PW91*/BS1: B3PW91*/STO-3G). The IR spectra suggest that there are two distinct and non-interconverting Cr(11) sites whose relative amounts differ on the two types of pretreated silica. The calculated upsilon(CO) frequencies for two model structures, ( SiO)(2)Cr(CO)(2) and ( SiO)(2)( Si2O)Cr(CO), agree well with experimental data, although these structures do not necessarily reflect the coordination of Cr(II) in the absence of CO. The X-ray absorption spectra reveal that the CO-free Cr(II) sites are coordinated by additional siloxane ligands, which may influence their ability to initiate ethylene polymerization. (C) 2012 Elsevier Inc. All rights reserved.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available