The Catalytic System Ti-Complex/MgCl2

Barbè, Pier Camillo; Cecchin, G.; Noristi, Luciano

doi:10.1007/978-3-662-15187-7_1

Cited by 24 publications

(24 citation statements)

References 90 publications

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“…The polymerization activity of the model catalyst calculated for a 1-cm 2 surface area would correspond to Ϸ75 g polypropylene per g catalyst per hr⅐atm and Ϸ1,400 g polyethylene per g catalyst per hr⅐atm for catalysts with a surface area of 50 m 2 ͞g. Industrial catalysts produce Ϸ100-500 g polypropylene per g catalyst per hr⅐atm and Ϸ2,000-10,000 g polyethylene per g catalyst per hr⅐atm (9). The fact that the model catalysts exhibit activities similar to the industrial catalysts suggests that the surface properties of the model catalysts prepared in UHV are relevant to those of industrial catalysts (25,26).…”

Section: Resultsmentioning

confidence: 99%

“…1b). For these compounds, the thermodynamically most stable surface is the (001) basal plane of the rhombohedral crystal structure (9,11). This surface is terminated with a close-packed chloride layer and the metal ion is shielded beneath this chloride layer (12)(13)(14).…”

Section: Strategy For Preparation Of Single-site Heterogeneous Zieglementioning

confidence: 99%

“…The current generation of Ziegler-Natta catalysts is composed of TiCl 4 species supported on high-surface-area magnesium chloride or magnesium ethoxide. This is the most productive form of the catalyst, evolved after several generations of formulations (7)(8)(9)(10). The monomer molecule adsorbs on the catalyst and reacts at the active catalyst site, preformed by reaction with Et 3 Al.…”

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confidence: 99%

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Surface science of single-site heterogeneous olefin polymerization catalysts

Kim

Somorjai

2006

Proc. Natl. Acad. Sci. U.S.A.

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This article reviews the surface science of the heterogeneous olefin polymerization catalysts. The specific focus is on how to prepare and characterize stereochemically specific heterogeneous model catalysts for the Ziegler-Natta polymerization. Under clean, ultrahigh vacuum conditions, low-energy electron irradiation during the chemical vapor deposition of model Ziegler-Natta catalysts can be used to create a ''single-site'' catalyst film with a surface structure that produces only isotactic polypropylene. The polymerization activities of the ultra-high vacuum-prepared model heterogeneous catalysts compare well with those of conventional Ziegler-Natta catalysts. X-ray photoelectron spectroscopic analyses identify the oxidation states of the Ti ions at the active sites. Temperature-programmed desorption distinguishes the binding strength of a probe molecule to the active sites that produce polypropylenes having different tacticities. These findings demonstrate that a surface science approach to the preparation and characterization of model heterogeneous catalysts can improve the catalyst design and provide fundamental understanding of the single-site olefin polymerization process.Ziegler-Natta C atalysts can function by being dispersed on solid surfaces (heterogeneous catalysis) or dissolved in reaction media (homogeneous catalysis). Heterogeneous catalysts are widely used in the chemical industry because they are in general easy to handle, separate, and recycle. Homogeneous catalysts are used in synthesis of specialty chemicals, offering precise control of molecular structure and reactivity. Combining the merits of these two different catalyst systems is of great interest for production of next-generation catalysts (1). In this article, we review the surface science of the heterogeneous olefin polymerization.In the polymerization of small olefins such as ethylene and propylene, both heterogeneous and homogeneous catalytic systems are operational (Fig. 1). Heterogeneous olefin polymerization catalysts (so-called Ziegler-Natta catalysts) are used for production of more than two-thirds of the commodity polyolefins consumed in the world (2, 3). Recently, a large number of specialty polyolefins have been produced with homogeneous metallocene catalysts (4). Whereas most industrial heterogeneous catalysts producing polyethylene and polypropylene are titanium chloride-based catalysts, the homogeneous metallocene catalysts are organometallic compounds of Ti, Zn, and Hf metals in organic solvents. In both types of catalysts, the catalytic species are activated with alkyl aluminum cocatalysts to create the active sites for carbon-carbon bond formation. Triethyl aluminum (AlEt 3 ) is widely used for heterogeneous ZieglerNatta catalysts, whereas methylaluminoxane is typically used for homogeneous metallocene catalysts.The polymers produced with these catalysts can have a wide range of mechanical properties depending on how many monomers are connected (molecular weight) and how they are connected (microstructure). The mechan...

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Section: Resultsmentioning

confidence: 99%

Section: Strategy For Preparation Of Single-site Heterogeneous Zieglementioning

confidence: 99%

mentioning

confidence: 99%

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Surface science of single-site heterogeneous olefin polymerization catalysts

Kim

Somorjai

2006

Proc. Natl. Acad. Sci. U.S.A.

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“…Based on these ESR studies and other kinetic studies, it has long been suggested and believed that only the Ti 3C species formed by AlEt 3 activation can polymerize propylene. 5 However, it should be noted that the Ti 2C and Ti 4C ions are not ESR active and >80% of total Ti 3C ions in the Ziegler-Natta catalysts are ESR silent due to interactions with the adjacent Ti 3C ions. 52,53 In situ measurements of both XPS and ESR for the same catalyst sample would provide the answer to this discrepancy.…”

Section: Titanium Oxidation States Of the Polymerization Sitesmentioning

confidence: 99%

Characterization of the Ziegler‐Natta olefin polymerization system: surface science studies on model catalysts

Kim

Somorjai

2001

Surface & Interface Analysis

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Modern surface science techniques have been applied to the heterogeneous Ziegler-Natta catalysis system, polymerizing a-olefins to produce polyolefins, and revealed the correlation between the catalyst surface structure and polymer properties. Two types of thin films -TiCl x /MgCl 2 and TiCl y /Au -were fabricated on an inert gold substrate, using chemical vapor deposition methods, to mimic the high-yield catalysts of MgCl 2 -supported TiCl 4 and TiCl 3 -based catalysts, respectively. Once activated with triethylaluminum (AlEt 3 ) vapor, both catalysts were active for polymerization of ethylene and propylene in the absence of excess AlEt 3 . The model catalyst films were as active as the high-surface-area industrial catalysts. Both catalysts were terminated with chlorine at the surface but had different surface structures. The TiCl x /MgCl 2 film had a distribution of two structures: the dominant sites had the (001) basal plane of these halide crystallites and the minority sites had a non-basal plane structure. The surface of the TiCl y /Au film assumed only the non-basal plane structure. These structural differences resulted in different tacticity of the polypropylene produced with these catalysts. The TiCl x /MgCl 2 catalyst produced both atactic and isotactic polypropylene, whereas the TiCl y catalyst without the MgCl 2 support produced exclusively isotactic polypropylene. The titanium oxidation states did not appear to be an important factor in determining the tacticity of the polypropylene.

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“…These polymers are suitable for an unlimited number of applications since they can now be tailored for one determined specification. In spite of the significant technical challenge in the development of the products and processes of polymerization, the catalyst is always the key factor, and the industrial success of a polymerization process depends greatly on the development of a proper catalyst system [1,2].…”

Section: Introductionmentioning

confidence: 99%

Role of Electron Donor in Polymer Catalyst Synthesis: An XPS Study

et al. 2007

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X-ray photoelectron spectroscopy (XPS) has been applied to the study pertaining to preparation and characterization of catalysts used in propylene polymerization. The analysis has indicated support/donor interaction in active support (adduct) and active support/TiCl 4 interaction during catalyst preparation process. A systematic study has been made to identify suitable adduct from a set of three adducts for catalyst synthesis. Precise binding energy of Titanium species on catalyst surface has been measured and its dispersion on support has been evaluated to correlate catalyst performance with the surface spectroscopic parameters.

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The Catalytic System Ti-Complex/MgCl2

Cited by 24 publications

References 90 publications

Surface science of single-site heterogeneous olefin polymerization catalysts

Surface science of single-site heterogeneous olefin polymerization catalysts

Characterization of the Ziegler‐Natta olefin polymerization system: surface science studies on model catalysts

Role of Electron Donor in Polymer Catalyst Synthesis: An XPS Study

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