ESR studies of ethylene interaction with active sites of supported organometallic catalysts for ethylene polymerization

1984 ◽  
Vol 25 (1-2) ◽  
pp. 33-38 ◽  
Author(s):  
V. A. Poluboyarov ◽  
G. A. Nesterov ◽  
V. A. Zakharov ◽  
V. P. Anufrienko
Keyword(s):  
Ethylene Polymerization ◽  
Active Sites ◽  
Organometallic Catalysts

scholarly journals Computational Investigation of the Role of Active Site Heterogeneity for a Supported Organovanadium(III) Hydrogenation Catalyst

2021 ◽  
Author(s):  
Prajay Patel ◽  
Robert Wells ◽  
David Kaphan ◽  
Massimiliano Delferro ◽  
Rex T. Skodje ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Density Functional ◽  
Computational Models ◽  
Surface Heterogeneity ◽  
Reaction Pathways ◽  
Spectroscopic Techniques ◽  
Organometallic Catalysts ◽  
Heterolytic Cleavage ◽  
Styrene Hydrogenation

<div> <div> <p></p><p><a>A crucial consideration for supported heterogeneous catalysts is the non-uniformity of the active sites, particularly for Supported Organometallic Catalysts (SOMCs). Standard spectroscopic techniques, such as X-ray absorption spectroscopy (XAS), reflect the nature of the most populated sites, which are often intrinsically structurally distinct from the most catalytically active sites. With computational models, often only a few representative structures are used to depict catalytic active sites on a surface, even though there are numerous observable factors of surface heterogeneity that contribute to the kinetically favorable active species. A previously reported study on the mechanism of a surface organovanadium(III) catalyst [(SiO)V<sup>III</sup>(Mes)(THF)] for styrene hydrogenation yielded two possible mechanisms: heterolytic cleavage and redox cycling. These two mechanistic scenarios are challenging to differentiate experimentally based on the kinetic readouts of the catalyst are identical. To showcase the importance of modeling surface heterogeneity and its effect on catalytic activity, density functional theory (DFT) computational models of a series of potential active sites of [(SiO)V<sup>III</sup>(Mes)(THF)] for the reaction pathways are applied in combination with kinetic Monte Carlo (kMC) simulations. Computed results were t then compared to the previously reported experimental kinetic study</a><a>.: 1) DFT free energy reaction pathways indicated the likely active site and pathway for styrene hydrogenation; a heterolytic cleavage pathway requiring a bare tripodal vanadium site. 2) From the kMC simulations, a mixture of the different bond lengths from the support oxygen to the metal center was required to qualitatively describe the experimentally observed kinetic aspects of a supported organovanadium(III) catalyst for olefin hydrogenation. </a>This work underscores the importance of modeling surface heterogeneity in computational catalysis.</p><p></p></div></div>

Ethylene polymerization over homogeneous Bis(imino)pyridine vanadium catalysts: data on the number and reactivity of active sites

2012 ◽  
Vol 19 (11) ◽  
Author(s):  
Artem A. Barabanov ◽  
Nina V. Semikolenova ◽  
Gennady D. Bukatov ◽  
Mikhail A. Matsko ◽  
Vladimir A. Zakharov
Keyword(s):  
Ethylene Polymerization ◽  
Active Sites ◽  
Vanadium Catalysts

scholarly journals Computational Investigation of the Role of Active Site Heterogeneity for a Supported Organovanadium(III) Hydrogenation Catalyst

2021 ◽  
Author(s):  
Prajay Patel ◽  
Robert Wells ◽  
David Kaphan ◽  
Massimiliano Delferro ◽  
Rex T. Skodje ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Density Functional ◽  
Computational Models ◽  
Surface Heterogeneity ◽  
Reaction Pathways ◽  
Spectroscopic Techniques ◽  
Organometallic Catalysts ◽  
Heterolytic Cleavage ◽  
Styrene Hydrogenation

<div> <div> <p></p><p><a>A crucial consideration for supported heterogeneous catalysts is the non-uniformity of the active sites, particularly for Supported Organometallic Catalysts (SOMCs). Standard spectroscopic techniques, such as X-ray absorption spectroscopy (XAS), reflect the nature of the most populated sites, which are often intrinsically structurally distinct from the most catalytically active sites. With computational models, often only a few representative structures are used to depict catalytic active sites on a surface, even though there are numerous observable factors of surface heterogeneity that contribute to the kinetically favorable active species. A previously reported study on the mechanism of a surface organovanadium(III) catalyst [(SiO)V<sup>III</sup>(Mes)(THF)] for styrene hydrogenation yielded two possible mechanisms: heterolytic cleavage and redox cycling. These two mechanistic scenarios are challenging to differentiate experimentally based on the kinetic readouts of the catalyst are identical. To showcase the importance of modeling surface heterogeneity and its effect on catalytic activity, density functional theory (DFT) computational models of a series of potential active sites of [(SiO)V<sup>III</sup>(Mes)(THF)] for the reaction pathways are applied in combination with kinetic Monte Carlo (kMC) simulations. Computed results were t then compared to the previously reported experimental kinetic study</a><a>.: 1) DFT free energy reaction pathways indicated the likely active site and pathway for styrene hydrogenation; a heterolytic cleavage pathway requiring a bare tripodal vanadium site. 2) From the kMC simulations, a mixture of the different bond lengths from the support oxygen to the metal center was required to qualitatively describe the experimentally observed kinetic aspects of a supported organovanadium(III) catalyst for olefin hydrogenation. </a>This work underscores the importance of modeling surface heterogeneity in computational catalysis.</p><p></p></div></div>

Formation of isolated titanium(III) ions in superactive titanium–magnesium catalysts with a low titanium content as active sites in ethylene polymerization

2014 ◽  
Vol 48 ◽  
pp. 38-40 ◽  
Author(s):  
Evgeny I. Koshevoy ◽  
Tatiana B. Mikenas ◽  
Vladimir A. Zakharov ◽  
Alexander M. Volodin ◽  
Roman M. Kenzhin
Keyword(s):  
Ethylene Polymerization ◽  
Active Sites ◽  
Titanium Content

scholarly journals α-Diimine Ni-Catalyzed Ethylene Polymerizations: On the Role of Nickel(I) Intermediates

Catalysts ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1386
Author(s):  
Igor E. Soshnikov ◽  
Nina V. Semikolenova ◽  
Konstantin P. Bryliakov ◽  
Evgenii P. Talsi
Keyword(s):  
Ethylene Polymerization ◽  
Active Sites ◽  
Rational Design ◽  
Catalytic Properties ◽  
Broad Class ◽  
Polymerization Process ◽  
Diimine Ligands ◽  
Catalyst Systems ◽  
Monovalent Nickel

Nickel(II) complexes with bidentate N,N-α-diimine ligands constitute a broad class of promising catalysts for the synthesis of branched polyethylenes via ethylene homopolymerization. Despite extensive studies devoted to the rational design of new Ni(II) α-diimines with desired catalytic properties, the polymerization mechanism has not been fully rationalized. In contrast to the well-characterized cationic Ni(II) active sites of ethylene polymerization and their precursors, the structure and role of Ni(I) species in the polymerization process continues to be a “black box”. This perspective discusses recent advances in the understanding of the nature and role of monovalent nickel complexes formed in Ni(II) α-diimine-based ethylene polymerization catalyst systems.

scholarly journals Impact of AlCl3 and FeCl2 Addition on Catalytic Behaviors of TiCl4/MgCl2/THF Catalysts for Ethylene Polymerization and Ethylene/1-Hexene Copolymerization

2018 ◽  
Vol 13 (3) ◽  
pp. 393
Author(s):  
Thanyathorn Niyomthai ◽  
Bunjerd Jongsomjit ◽  
Piyasan Praserthdam
Keyword(s):  
Catalytic Activity ◽  
Active Center ◽  
Chemical Reaction ◽  
Lewis Acids ◽  
Ethylene Polymerization ◽  
Active Sites ◽  
Reaction Engineering ◽  
Chemical Route ◽  
The Impact ◽  
Chemical Reaction Engineering

The present research focuses on elucidating of the impact of Lewis acids including AlCl3 and FeCl2 addition on catalytic behaviors during ethylene polymerization and ethylene/1-hexene copolymerization over the TiCl4/MgCl2/THF catalyst (Cat. A). In this study, the Cat. A with the absence and presence of Lewis acids was synthesized via the chemical route. Then, all catalyst samples were characterized and tested in the slurry polymerization. For ethylene polymerization, using the Cat. A with the presence of AlCl3 apparently gave the highest activity among other catalysts. In addition, the activity of catalysts tended to increase with the presence of the Lewis acids. This can be attributed to an enhancement of active center distribution by the addition of Lewis acids leading to larger amounts of the isolated Ti species. Moreover, with the presence of Lewis acids, the effect of hydrogen on the decreased activity was also less pronounced. Considering ethylene/1-hexene copolymerization, it revealed that the catalyst with the presence of mixed Lewis acids (AlCl3 + FeCl2) exhibited the highest activity. It is suggested that the presence of mixed Lewis acids possibly caused a change in acidity of active sites, which is suitable for copolymerization. However, activities of all catalysts in ethylene/1-hexene copolymerization were lower than those in ethylene polymerization. The effect of hydrogen on the decreased activity for both polymerization and copolymerization system was found to be similar with the presence of Lewis acids. Based on this study, it is quite promising to enhance the catalytic activity by addition of proper Lewis acids, especially when the pressure of hydrogen increases. The characteristics of polymers obtained upon the presence of Lewis acids will be discussed further in more detail.  Copyright © 2018 BCREC Group. All rights reservedReceived: 22nd January 2018; Revised: 18th March 2018; Accepted: 19th March 2018How to Cite: Niyomthai, T., Jongsomjit, B., Praserthdam, P. (2018). Impact of AlCl3 and FeCl2 Addition on Catalytic Behaviors of TiCl4/MgCl2/THF Catalysts for Ethylene Polymerization and Ethylene/1-Hexene Copolymerization. Bulletin of Chemical Reaction Engineering & Catalysis, 13 (3): 393-404 (doi:10.9767/bcrec.13.3.2116.393-404)Permalink/DOI: https://doi.org/10.9767/bcrec.13.3.2116.393-404

scholarly journals ORGANOMETALLIC CATALYSTS FOR ETHYLENE POLYMERIZATION

2021 ◽  
pp. 92-96
Author(s):  
TATYANA ANDREEVNA RODINA ◽  
Keyword(s):  
Mechanical Properties ◽  
Ethylene Polymerization ◽  
Physical And Mechanical Properties ◽  
Low Pressure ◽  
Comparative Characteristic ◽  
Organometallic Catalysts

The use of organometallic catalysts in ethylene polymerization at low pressure is considered. A comparative characteristic of different generations of catalysts and their influence on the physical and mechanical properties of polymers is given.

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