Structure of Monolayer and Multilayer Magnesium Chloride Films Grown on Pd(111)

Fairbrother, D. Howard; Roberts, Joel G.; Rizzi, and Simone; Somorjai, Gábor A.

doi:10.1021/la960680c

Cited by 39 publications

(50 citation statements)

References 14 publications

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“…2͑b͒. This structure has been reported before by Fairbrother et al 18,22 as an epitaxial monolayer, where according to the lattice constants of Pd͑111͒ and MgCl 2 (001), three unit cells of MgCl 2 (001) fit onto four Pd͑111͒ cells. A schematic representation of this situation is shown in Fig.…”

Section: Resultssupporting

confidence: 73%

Characterization of a model Ziegler–Natta catalyst for ethylene polymerization

Schmidt

Risse

Hamann

et al. 2002

The Journal of Chemical Physics

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Section: Resultssupporting

confidence: 73%

Characterization of a model Ziegler–Natta catalyst for ethylene polymerization

Schmidt

Risse

Hamann

et al. 2002

The Journal of Chemical Physics

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“…This method has been applied successfully in the surface structural investigations of other large band gap materials [5][6][7][8]. More specifically, it was used in the surface structure determination of NaCl(100), whose LEED determined structure is analogous to the LiF(100) surface structure [7], see Table 2.…”

Section: Introductionmentioning

confidence: 99%

Surface structural analysis of LiF() thin films grown on Pt()

Roberts¹,

Hove²,

Somorjai³

2002

Surface Science

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The surface structure of a multilayer LiF(100) thin film grown on Pt(111) from the vapor has been determined by the automated tensor low energy electron diffraction (LEED) method. The final structure, which refined to a Pendry Rfactor (R P ) of 0.24, had a surface corrugation (∆ 1 ) of 0.24±0.04 Å due to the Li + being displaced towards the bulk, leaving the initially coplanar F -unshifted. A similar intralayer corrugation due to the movement of the Li + was also observed in the layer immediately under the surface layer, although to a lesser degree:

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“…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. The high-temperature desorption peak can be attributed to the nonbasal planes or defects in the ionic lattice of the basal plane where the surface chloride ions are not close-packed and the metal ions beneath the chloride layer are undercoordinated.…”

Section: Resultsmentioning

confidence: 99%

“…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). Because of this structure, the (001) surface has a very low reactivity and is difficult to activate for polymerization (15,16).…”

Section: Strategy For Preparation Of Single-site Heterogeneous Zieglementioning

confidence: 99%

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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Structure of Monolayer and Multilayer Magnesium Chloride Films Grown on Pd(111)

Cited by 39 publications

References 14 publications

Characterization of a model Ziegler–Natta catalyst for ethylene polymerization

Characterization of a model Ziegler–Natta catalyst for ethylene polymerization

Surface structural analysis of LiF() thin films grown on Pt()

Surface science of single-site heterogeneous olefin polymerization catalysts

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