دانلود رایگان مقاله لاتین پلیمریزاسیون اتیلن توسط کروم از سایت الزویر
عنوان فارسی مقاله:
پلیمریزاسیون اتیلن توسط کروم (III) نمک در حامل های اسیدی
عنوان انگلیسی مقاله:
Ethylene polymerization by Cr(III) salts on acidic carriers
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
One of the most important ways of studying polymerization catalysts is to examine the polymer that they produce. This is because the active site population is usually only a small fraction of the total metal loading. Thus the only certain way of selectively probing the active sites is by examining the catalyst activity, and the character of the polymer produced. Acidic, high-porosity oxide carriers have been found to activate a wide variety of transition metal compounds to generate olefin polymerization catalysts. This includes Phillips hexavalent Cr/silica catalysts, in which the addition of titania, alumina or other metal oxides increase the surface acidity. Consequently the polymerization rate and some polymer characteristics are significantly enhanced [1,2]. In other examples, the addition fluoride, phosphate or sulfate to Cr(VI)/alumina, which also enhances surface acidity, produced a similar boost in activity [3–6]. Indeed, many lower-valent Cr alkyl or arene compounds do not polymerize ethylene unless deposited onto an acidic oxide support[1,7–10]. Other examples include nickel compounds which were enhanced by acidic aluminophosphate carriers [11,12], and vanadium (II) andtitanium (II) alkyls [13]. Even metallocenes [14–17] and single-site coordination compounds [18–22] can be activated by deposition onto a wide variety of such solid acid supports. In each of these catalytic systems the acidic support is thought to withdraw electron density from the transition metal, thus rendering it more reactive with the olefinic pi-orbitals. In this paper we report that chromium (III) 2,4-pentanedionate, i.e. Cr(AcAc)3, can also be activated by these acidic carriers [23]. This compound has long been used as a source of Cr in the production of Phillips Cr(VI)/silica catalysts [24–29]. However, in this capacity it is calcined in air at >500 ◦C, which burns off the 2,4- pentanedionate ligands, leaving a typical Cr(VI) oxide (Phillips) catalyst. In contrast, we report here that Cr(AcAc)3 can itself initiate ethylene polymerization at high rates in the absence of calcination, if it is supported on an acidic carrier. Unlike the Cr alkyl and arene compounds described above, which already contain a potential Cr-alkyl initiation site, Cr(AcAc)3 requires an aluminum alkyl cocatalyst in order to generate polymerization activity. Possibly one of the 2,4-pentanedionate ligands is replaced by an alkyl group as the initiating species. In this report we describe some of the unusual characteristics of this catalyst system, and the polyethylene it produces. These observations suggest that the choice of acidic support has a much stronger influence on the catalyst than the initial organic ligands.
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کلمات کلیدی:
Comparison of ethylene polymerization catalyzed over Cr (VI)/silica ... link.springer.com/article/10.1007/BF00558058 by CS Kim - 1992 - Cited by 10 - Related articles Summary. Ethylene polymerization and the morphology of produced high density polyethylene (HDPE) catalyzed over. Cr(VI)/silica and Cr(II)/silica were studied. Phillips Cr/Silica Catalyst for Ethylene Polymerization - Springer link.springer.com/chapter/10.1007%2F12_2013_222 by R Cheng - 2013 - Cited by 17 - Related articles Jul 7, 2013 - Ethylene polymerization mechanisms Heterogeneous model catalysts Homogeneous model catalysts Molecular modeling Phillips Cr/silica ... Identification of Cr oxidation state active in ethylene polymerization on ... link.springer.com/article/10.1007/BF00765035 by PA Zielinski - 1992 - Cited by 15 - Related articles Abstract. High temperature treatment under vacuum or in a pure N2 atmosphere can be used instead of a reduction step to activate Cr/SiO2 catalysts used for ... Ethylene-polymerization by surface supported Cr(IV) species: possible ... www.nrcresearchpress.com/doi/abs/10.1139/v99-242 by R Schmid - 2000 - Cited by 37 - Related articles Possible reaction mechanisms of olefin polymerization catalyzed by surface supported Cr(IV) species have been investigated by first principles density ... Effect of F-modification over Phillips Cr/SiO2 catalyst for ethylene ... onlinelibrary.wiley.com/doi/10.1002/cctc.201700375/abstract by QQ Sun - 2017 Apr 25, 2017 - ... over Phillips Cr/SiO2 catalyst for ethylene polymerization ... of the polyethylene produced by the fluoride modified Phillips Cr/F-SiO2 catalyst. [PDF]The Active Site of the Phillip's Ethylene Polymerization Catalyst www.nacatsoc.org/21nam/data/papers/Paper1509.pdf The Phillips ethylene polymerization catalyst has been a primary route to the ... conditions of ethylene polymerization, the so-generated Cr(II) was titrated with ... Searches related to Ethylene polymerization by Cr cr2+ name cu2+ electron configuration
