A surface science model for the Phillips ethylene polymerization catalyst: thermal activation and polymerization activity

Kimmenade, E.M.E. van; Kuiper, A. E. T.; Tamminga, Y.; Thüne, Peter C.; Niemantsverdriet, J.W.

doi:10.1016/j.jcat.2003.12.019

Cited by 60 publications

(34 citation statements)

References 28 publications

(38 reference statements)

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“…Elemental density analysis was determined from XPS based on the method described in a previous report. [7] In that reference, one could quantify the coverage of Chromium (less than a monolayer) on a flat Silica surface according to the intensity of the XPS spectra, in combination with Rutherford Backscattering Spectrometry (RBS). Coverage of other elements was calculated using the photoionization cross section.…”

Section: General Information and Materialsmentioning

confidence: 99%

“…[5][6][7] Such models are based on silicon (100) single crystals covered with a thin layer of silica (20 nm) with a surface roughness below 1 nm. Later on, this model was also applied to silica-supported single-site catalysts.…”

Section: Introductionmentioning

confidence: 99%

“…The similar binding energies and features of the Fe 2p spectra of complex 6 and 2, see Figure 1(a), suggests a very close chemical environment for iron in both precursors. Apart from determining the presence and chemical state of different elements, after combining the results from the method previously reported [7] and the photoionzation cross section, [11] one can readily estimate the elemental densities on the flat silica surface from the XPS peak intensities. On surface 5, a nitrogen density of 1.7 N Á nm À2 is detected by XPS, which indicates a ligand density of 0.6 nm À2 (spectrum not shown here).…”

Section: Introductionmentioning

confidence: 99%

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Introducing a Flat Model of the Silica‐Supported Bis(imino)pyridyl Iron(II) Polyolefin Catalyst

Han

Müller

Vogt

et al. 2006

Macromol. Rapid Commun.

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Summary: A well‐defined flat model of a supported homogeneous polyolefin catalyst is prepared on the basis of an immobilized bis(imino)pyridyl iron complex on a super flat silica surface. The amount of supported catalyst precursor is quantified using XPS. This model catalyst remains active over extended periods, i.e., an average activity of 0.25 × 103 kg PE · (molCat · h · bar)−1 is obtained for 24 h of ethylene polymerization. The morphology of the nascent polyethylene film is investigated by SEM.A side‐view SEM image of the PE produced from the supported bis(imino)pyridyl Fe catalyst.magnified imageA side‐view SEM image of the PE produced from the supported bis(imino)pyridyl Fe catalyst.

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Section: General Information and Materialsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Introducing a Flat Model of the Silica‐Supported Bis(imino)pyridyl Iron(II) Polyolefin Catalyst

Han

Müller

Vogt

et al. 2006

Macromol. Rapid Commun.

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“…In the past several years we have developed a flat model catalyst based on a silicon wafer covered with about 20 nm of thermal silicon oxide [17][18][19][20][21][22][23]. With this model we eventually aim to arrive at creating a complete molecular level picture of the Cr/silica ethylene polymerization catalyst by correlating catalyst preparation, characterization of the active surface and polymerization activity.…”

Section: Introductionmentioning

confidence: 99%

Visualization of local ethylene polymerization activity on a flat CrO x /SiO2/Si(100) model catalyst

et al. 2007

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Flat model catalysts give access to fundamental aspects of olefin polymerization over heterogeneous catalysts. They are especially suited for the investigation on the early stages of polymer film growth employing scanning probe and electron microscopy. The polymerization centers are confined to a well defined two dimensional plane that remains constant during the polymerization. Using the Phillips (CrO x /SiO 2 ) catalyst as an example we demonstrate how this approach can be used do visualize the lateral distribution of polymerization activity in the initial stages of polymer growth.

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“…[14,[17][18][19] It is worth mentioning that the system that results from the impregnation of the silica fibers with H 2 CrO 4 (Scheme 1b) can be considered as a model version of the Phillips catalyst because the crystalline nature of the fibers and their low surface area should, in principle, allow the grafting of well-isolated and homogeneous Cr species. [20][21][22] The presence of a PE coating and the morphology of the resulting material were investigated by means of microRaman spectroscopy and SEM, respectively. SEM images of the silica microfibers before (Scheme 1a) and after 5 h of in situ C 2 H 4 polymerization (Scheme 1d) are reported in Figure 1a and b, respectively.…”

mentioning

confidence: 99%

Polyethylene Microtubes from Silica Fiber‐based Polyethylene Composites Synthesized by an In Situ Catalytic Method

et al. 2006

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Most composite materials that consist of a thermoplastic matrix and a particulate filler are prepared by mechanical mixing of the components above the melting temperature of the polymer. Both organic (e.g., poly-p-(phenylene terephthalamide): PpPTA, polyethylene: PE) and inorganic (carbon, glass) fibers are extensively used as fillers for polymer-based composite materials; in particular, silica fibers combine the advantages of high tensile and compressive strengths with low cost, when compared to other competing fibers. [1,2] PE is one of the polymers most often used as a matrix because of its chemical resistance to solvents, low friction coefficient, hydrophobicity, and biocompatibility.[3]However, the mechanical mixing of components does not allow a fine and homogeneous dispersion of the filler, [4,5] and the resulting material is usually characterized by poor mechanical properties. In order to improve the properties of the resulting composite, a direct connection of the polymer with the surface of the filler is highly desirable. The polymerization filling technique (PFT) has proved very efficient in this regard. This method, initially investigated in Ziegler-Natta polymerization [6][7][8] and more recently developed for metallocene catalysis applied to a broad range of microfillers (e.g., kaolin, silica, carbon nanotubes, and graphite), [9][10][11] consists of anchoring a polymerization catalyst directly onto the filler surface, followed by its activation with a cocatalyst. The polymer chains grow directly from the catalytic species upon in situ addition of the monomer, and for this reason the polymer is formed in very close contact with the filler surface. Such a technique leads to a much more uniform filler distribution and a considerably enhanced interfacial adhesion, even at high filler content, compared to conventional mechanical techniques. In this work we present an original method to realize silicamicrofiber-based PE composites, which relies upon the in situ polymerization of ethylene from the gas phase, catalyzed by active Cr species anchored onto the surface of the silica microfibers. As a result, silica microfibers are homogeneously coated and interconnected by the PE chains grown in situ, forming a promising composite material without the need for post-synthesis processing. With respect to the PFT technique mentioned above, this "microprocessing" method is much cleaner because it does not require the use of cocatalysts and solvents. In particular, we demonstrate that by properly tuning the reaction conditions, it is possible to move from wellisolated to exclusively interconnected homogeneously PEcoated silica fibers, which finally constitute a real microcomposite material. The possibility of realizing a well-defined PE coating on silica microfibers can be used in an inverse way, i.e., by considering the silica microfibers as templates for the realization of PE microtubes. Here, we demonstrate that removal of the internal silica core from the composite material indeed results in the formation of PE ...

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A surface science model for the Phillips ethylene polymerization catalyst: thermal activation and polymerization activity

Cited by 60 publications

References 28 publications

Introducing a Flat Model of the Silica‐Supported Bis(imino)pyridyl Iron(II) Polyolefin Catalyst

Introducing a Flat Model of the Silica‐Supported Bis(imino)pyridyl Iron(II) Polyolefin Catalyst

Visualization of local ethylene polymerization activity on a flat CrO x /SiO2/Si(100) model catalyst

Polyethylene Microtubes from Silica Fiber‐based Polyethylene Composites Synthesized by an In Situ Catalytic Method

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