Metathesis activity of monomeric Mo-methylidene centres on (100) and (110)C surfaces of γ-Al2O3––a comparative DFT study

Handzlik, Jarosław

doi:10.1016/j.susc.2004.05.016

Cited by 16 publications

(24 citation statements)

References 82 publications

(104 reference statements)

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“…Selected bond lengths and bond orders for the Mo−methylidene and molybdacyclobutane centers are listed in Table . The predicted Mo−C1 distance in a1 is close to the carbene bond length of the four-coordinate Mo−alkylidene complex (1.880 Å), , as well as to the calculated MoC lengths for Mo−methylidene centers replacing bridge hydroxyl groups on alumina. , The MoC bond order for a1 is also very similar to the previously calculated values for the Mo−methylidene sites on alumina. , The NBO analysis confirms that one σ and one π bond contribute to the overall MoC bond. In the σ-NBO, 37% of the charge is polarized toward the Mo, while in the π-NBO the electron density is almost equally distributed between both atoms (52% toward the Mo).…”

Section: Ethene Metathesis On Mo−methylidene Centers On Silicasupporting

confidence: 84%

“…In the case of the supported catalysts, the carrier can be considered as a ligand of the metal center. , Therefore, analogously to the homogeneous metathesis catalysts, the local properties of the support should influence the reactivity of the active sites. Indeed, our previous theoretical work concerning heterogeneous molybdena−alumina systems , proved that location of the monomeric Mo−alkylidene center on γ-alumina affects its reactivity toward alkene. Both local electronic properties of the carrier and geometry of the active site, the factors depending on the Mo center location, influence the activation barriers, as well as the stabilities of the molybdacyclobutane intermediates.…”

Section: Introductionmentioning

confidence: 99%

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Metathesis Activity and Properties of Mo−Alkylidene Sites Differently Located on Silica. A Density Functional Theory Study

Handzlik

2005

J. Phys. Chem. B

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Ethene metathesis proceeding on Mo-methylidene centers on silica is investigated with density functional theory, applying the cluster approach. Three different locations of the active sites are considered, in which the Mo center replaces a pair of geminal silanols, two silanols from adjacent geminal pairs and two single silanols, respectively. It is shown that metathesis activity of the Mo-methylidene sites strongly depends on their location on silica. Different reactivity of the centers toward alkene is explained by differences in their geometrical and electronic structure parameters. The calculated C-H stretching vibrations of the proposed Mo-methylidene, Mo-ethylidene, and molybdacyclobutane surface complexes are well consistent with the reported IR spectra for the corresponding species generated on real molybdena-silica catalysts. On the basis of the obtained results it is proposed that among the studied cases, the Mo centers replacing two silanols from adjacent geminal pairs of silica surface are the most adequate models of the real active sites.

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Section: Ethene Metathesis On Mo−methylidene Centers On Silicasupporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Metathesis Activity and Properties of Mo−Alkylidene Sites Differently Located on Silica. A Density Functional Theory Study

Handzlik

2005

J. Phys. Chem. B

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“…As the conversion of the TBP intermediate to the SP molybdacyclobutane is concerned, the increase of the system size also affects the calculated energies, although to a less extent. It was mentioned earlier that this elementary step can be responsible for the reversible deactivation of the catalyst [29,[52][53][54]. When the larger model 4 is applied, this transformation is predicted to proceed easier than in the case of the model 2 (Table II).…”

Section: The Size Of the Inner Layer And The Whole Systemmentioning

confidence: 83%

“…The first reaction is necessary to continue the catalytic cycle of olefin metathesis and is almost identical to the reverse step, because of symmetry of the molybdacyclobutane ring. The second reaction can be considered as a reversible deactivation step [29,[52][53][54]. In Figure 2, both molyb-dacyclobutane structures (TBP and SP) as well as the corresponding transition state geometries (TS-1 and TS-2) are presented for the example path of ethene metathesis proceeding on the center 2.…”

Section: Mechanism Of Ethene Metathesismentioning

confidence: 99%

Application of the ONIOM (QM/QM) method in the study of molybdena–silica system active in olefin metathesis

Handzlik

2007

Int J of Quantum Chemistry

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ABSTRACT:The two-layer ONIOM method is applied for description of Momethylidene center on silica, which is the active site of olefin metathesis. Two clusters of different size are employed to model the silica surface. For the larger one, two differently defined inner layers (the model systems) are tested. In all the calculations, the B3LYP functional is adopted for the inner layer, while the Hartree-Fock method or the local density approximation (SVWN5 functional) is used for the treatment of the real system. Based on the reference results obtained for the real system from the B3LYP calculations, it is concluded that both B3LYP:HF and B3LYP:SVWN5 schemes are suitable for proper description of the geometry of the Mo center and its activity in ethene metathesis. The former combination is a little better choice, however. It is also shown that the inner layer, including the third coordination sphere of molybdenum, is large enough to obtain satisfactory results. On the other hand, the relative energies and some geometrical parameters of the active site are dependent on the size of the entire system studied. The sensitivity of the geometrical parameters and reaction energies to the changes of the scale factor g, involved in the ONIOM scheme, is studied as well. It is concluded that the link atom distance is not crucial for obtaining correct results.

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“…Theoretical studies were done by Handzlik and coworkers using density functional theory (DFT) for propene and ethene metathesis proceeding on monomeric Mo centers of molybdena-alumina catalysts [24][25][26][27]. They studied the pathway of ethene and propene metathesis on monomeric Mo(VI) centers of an MoO 3 /Al 2 O 3 catalyst.…”

Section: Mechanismmentioning

confidence: 99%

Metathesis of Alkenes

Mol

Leeuwen

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Scope of the Reaction Acyclic Alkenes Alkadienes Cyclic Alkenes Ring‐Opening Metathesis Metathesis Catalysts Solid Metathesis Catalysts Mechanism Molybdenum Catalysts Mo O 3 / Al 2 O 3 Effect of Impurities Mo O 3 / Si O 2 Tungsten Catalysts WO 3 / Al 2 O 3 WO 3 / Si O 2 Rhenium Re 2 O 7 / Al 2 O 3 A Catalyst Characterization B Particle Size C Catalytic Activity D Selectivity Modified Re 2 O 7 / Al 2 O 3 Catalysts A Role of the Promoter B Catalyst Deactivation Kinetics Industrial Applications The P hillips T riolefin Process The Meta‐4 Process Production of 1‐Hexene Production of Neohexene SHOP Production of Fine Chemicals Conclusions

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Metathesis activity of monomeric Mo-methylidene centres on (100) and (110)C surfaces of γ-Al2O3––a comparative DFT study

Cited by 16 publications

References 82 publications

Metathesis Activity and Properties of Mo−Alkylidene Sites Differently Located on Silica. A Density Functional Theory Study

Metathesis Activity and Properties of Mo−Alkylidene Sites Differently Located on Silica. A Density Functional Theory Study

Application of the ONIOM (QM/QM) method in the study of molybdena–silica system active in olefin metathesis

Metathesis of Alkenes

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