An FTIR spectroscopic view of the initiation of ethylene polymerization on Cr/SiO2 catalyst
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Cited by (32)
Active sites formation and their transformations during ethylene polymerization by the Phillips CrO<inf>x</inf>/SiO<inf>2</inf> catalyst
2017, Journal of CatalysisCitation Excerpt :Another possible proton transfer reaction can generate Cr(IV) vinyl hydride site 3A10 (Fig. 3). Such a structure was proposed in the literature as an active intermediate [33,37]. Geometry analysis suggests that the carbon atoms in 3A1 have sp3 hybridization rather than sp2, in contrast to the π-complex 5A1.
A Review of the Phillips Supported Chromium Catalyst and Its Commercial Use for Ethylene Polymerization
2010, Advances in CatalysisInfrared Spectroscopy of Transient Surface Species
2007, Advances in CatalysisCitation Excerpt :After the creation of Y2 groups, the mechanism proceeds via insertion of ethene, with formation of the intermediate represented in square brackets. This model explains well the experimentally observed first-order behavior of the polymerization reaction with respect to the monomer partial pressure (218–224). The aim of this Section is to discuss the experimental methods, problems, and recent improvements in the determination of the exact nature of the precursor species Y1, Y2, Y3, etc. (i.e., the determination of the initiation mechanism for the ethene polymerization).
In situ FTIR spectroscopy of key intermediates in the first stages of ethylene polymerization on the Cr/SiO<inf>2</inf> Phillips catalyst: Solving the puzzle of the initiation mechanism?
2006, Journal of CatalysisCitation Excerpt :Several spectroscopic techniques have been adopted to highlight the coordination environment of the surface Cr species. From UV–vis DRS [5–9], FTIR spectroscopy of adsorbed probe molecules (CO, NO, CO2, N2O, pyridine, and, more recently, H2 and N2) [5,10–24], Raman spectroscopy [5,9,25,26], resonant or preresonant Raman spectroscopy [27,28], XAS [5,8,29], and XPS [5,30,31], an extremely complex and heterogeneous scenario has emerged, reflecting the high heterogeneity of the silica support [5]. Recently, we demonstrated a precise relationship between the structure of the precursors of the Cr active sites, the polymerization activity, and the properties of the resulting polymers [32].
In situ, Cr K-edge XAS study on the Phillips catalyst: Activation and ethylene polymerization
2005, Journal of CatalysisCitation Excerpt :The structure of Cr(II) and, to a lesser extent, the average valence state of the reduced chromium on the silica surface have been widely investigated in the past with several spectroscopic and chemical techniques. Using XPS, UV–Vis, and IR spectroscopies, several authors [3,5,7,12,13,18–27] found that the average oxidation state of Cr in the model catalyst is just above 2; here the catalyst comprises mainly anchored Cr(II) and a variable amount of pseudo-octahedral Cr(III) species (presumably in the form of α-Cr2O3). From this brief introduction, it is clear that the problem of the structure of chromium on the Phillips catalyst is still an open question.
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On leave from Technical University of Lodz, Poland.