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Surface physico‐chemical state of CO‐prereduced Phillips CrO x /SiO 2 catalyst and unique polymerization behavior in the presence of Al‐alkyl cocatalyst
Author(s) -
Liu Boping,
Fang Yuwei,
Nakatani Hisayuki,
Terano Minoru
Publication year - 2004
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.200450905
Subject(s) - catalysis , x ray photoelectron spectroscopy , desorption , chromate conversion coating , polymerization , alkyl , adsorption , ethylene , calcination , chemistry , materials science , inorganic chemistry , chemical engineering , organic chemistry , chromium , polymer , engineering
Abstract In this work, a CO‐prereduced Phillips CrO x /SiO 2 catalyst (PC600/CO) was characterized by X‐ray photoelectron spectroscopy (XPS) and temperature programmed desorption with mass spectrometer (TPD‐MS) in comparison with a calcined catalyst (PC600). It was found that surface chromate Cr(VI) species had not been completely reduced into Cr(II) species, meanwhile, CO and CO 2 still strongly adsorbed on the PC600/CO catalyst. Subsequently, the unique real‐time profiles of ethylene polymerization rate using PC600/CO in the presence of TEA indicated the existence of two types of active sites: the first type derived from the desorption of CO or CO 2 from Cr(II) species by alkyl‐Al and featured with fast activation, higher activity and fast decay; the second type generated from the further reduction of residual chromate Cr(VI) species by alkyl‐Al and featured with slow activation, lower activity and slow decay.