Surface Characterization of the TiClx/MgCl2 Model Ziegler−Natta Polymerization Catalysts:  Adsorption Site Studies Using Mesitylene Thermal Desorption

Kim, Seong Han; Tewell, Craig R.; Somorjai, Gábor A.

doi:10.1021/la000194w

Cited by 24 publications

(42 citation statements)

References 41 publications

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“…Fig. 7 displays the mesitylene TPD results for a well characterized MgCl 2 support film produced by thermal evaporation of MgCl 2 on Au (20). From structural information on the MgCl 2 film (12)(13)(14), the Ϸ200-K desorption site is attributed to the (001) basal plane structure where the chloride ions at the outermost layer are close-packed and the metal ions under the chloride layer are coordinated to six chloride ions.…”

Section: Resultsmentioning

confidence: 99%

“…Because of their high cross-sections in interactions with the condensed phase, these charged particles interact mostly with surface species. In the case of electrons, the surface chloride ions are removed by electron-induced desorption (20).…”

Section: Synthesis Of Heterogeneous Ziegler-natta Model Catalysts Undmentioning

confidence: 99%

“…The oxidation states of the titanium species have a distribution of 4ϩ, 3ϩ, and 2ϩ. When these films are irradiated with low-energy electrons and ions, some fraction of surface chlorine ions are desorbed into vacuum, leaving undercoordinated metal ions at the surface (17,20). However, these defective surfaces are readily converted to the stable structure by diffusion of chloride ions from the underlayers (20).…”

Section: Synthesis Of Heterogeneous Ziegler-natta Model Catalysts Undmentioning

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: Synthesis Of Heterogeneous Ziegler-natta Model Catalysts Undmentioning

confidence: 99%

Section: Synthesis Of Heterogeneous Ziegler-natta Model Catalysts Undmentioning

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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“…12 The TiCl y /MgCl 2 film grown at 300 K had the Ti oxidation state distribution similar to that of TiCl y /Au grown at 300 K. Angle-resolved XPS analysis indicated that both TiCl y films consist of a monolayer of Ti The adsorption site distribution on the model Ziegler-Natta catalyst surfaces was detected with TPD as a weakly bound probe molecule that leaves the catalyst surface chemically undisturbed. 15,20 Mesitylene was the best among the probe molecules tested in our laboratory. 15 Although this method could not distinguish the metal composition and oxidation state due to chlorine termination of the catalyst surface, it could differentiate the different adsorption sites depending on the heat of adsorption, which in turn depended on the surface chlorine structure.…”

Section: The Ticl Y Multilayer Film As a Model System For The Ticl 3 mentioning

confidence: 94%

“…In TPD of the mesitylenecovered catalyst surface, the heat of mesitylene desorption provided information about the surface structure of the model catalyst film. 15,20,21 The polymerization rate on the model catalyst was measured with LRI. This technique is based on the refractive index difference between the polymer and the catalyst.…”

Section: Surface Science Approachesmentioning

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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Ziegler‐Natta Catalysts

Fisch

2019

Kirk-Othmer Encyclopedia of Chemical Technology

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The development of polymers has made daily activities more pleasant. Polyolefins, mainly polyethylene and polypropylene, are used in large scale by society thanks to its wide properties and affordable costs. This remarkable achievement initiated by the research work conducted by professors Ziegler and Natta, by which both were awarded with the Nobel Prize due to the discovery of a catalytic route for producing polyethylene and polypropylene of outstanding properties. Owing to the social importance of this discovery, the catalyst is known as Ziegler‐Natta by society. The modern versions of the Ziegler‐Natta catalyst are typically composed by a transition metal (Ti or V), aluminum alkyl (AlEt 3 ), and Lewis base (diesters; electron donor) all immobilized on a support (MgCl 2 ).

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Surface Characterization of the TiCl_x/MgCl₂ Model Ziegler−Natta Polymerization Catalysts: Adsorption Site Studies Using Mesitylene Thermal Desorption

Cited by 24 publications

References 41 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

Ziegler‐Natta Catalysts

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