文献类型：期刊文献

英文题名：Spectroscopic and structural characterization of Cr(II)/SiO2 active site precursors in model Phillips polymerization catalysts

作者：Zhong, Lei[1,2]; Lee, Ming-Yung[2]; Liu, Zhen[1]; Wanglee, Ying-Jen[3]; Liu, Boping[1]; Scott, Susannah L.[2,3]

机构：[1] State Key Laboratory of Chemical Engineering, East China University of Science and Technology, 130 Meilong Road, 200237 Shanghai, China; [2] Department of Chemical Engineering, University of California, Santa Barbara, CA 93106-5080, United States; [3] Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-9510, United States

年份：2012

卷号：293

起止页码：1

外文期刊名：Journal of Catalysis

收录：EI(收录号：20123315346403)

语种：英文

外文关键词：Ethylene - Model structures - Catalyst activity - Chlorine compounds - Chromates - X ray absorption spectroscopy - Polymerization

摘要：Compositionally and structurally uniform chromate sites grafted onto silica via the ambient temperature reaction of CrO2Cl2 with silica pretreated at either 500 or 800 °C, followed by mild heating at 300 °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(II) sites whose relative amounts differ on the two types of pretreated silica. The calculated υCO frequencies for two model structures, (SiO)2Cr(CO)2 and (SiO)2(Si 2O)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. ? 2012 Elsevier Inc. All rights reserved.