KMITL

Permanent URI for this communityhttps://dspace.kmitl.ac.th/handle/kmitl/1

Browse

Settings

Access type: UnknownAuthor: search.filters.author.Tantanak, Duangkamol

Search Results

Now showing 1 - 2 of 2
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    Application of ONIOM calculations in the study of the effect of the zeolite framework on the adsorption of alkenes to ZSM-5
    (2006-08-18)
    Namuangruk, Supawadee
    ;
    Tantanak, Duangkamol
    ;
    Limtrakul, Jumras
    The structures and energetics associated with the adsorption of ethene and four butene isomers on H-ZSM-5 zeolite have been studied using a 46T cluster and calculated at the ONIOM2(B3LYP/6-311++G(d,p):UFF) level. The adsorption energy for ethene-zeolite complex is predicted to be -8.17 kcal/mol, which is in good agreement with the experimental data of -9.0 kcal/mol. The trend of the calculated adsorption energies (kcal/mol) for the butene isomers is as follows: 1-butene (-16.06) > cis-2-butene (-13.62) ≅ trans-2-butene (-13.25) > isobutene (-6.96). The isobutene-zeolite complex is the least stable due to the greatest steric repulsion between the methyl substituents around the C{double bond, long}C bond and zeolite framework; the more substituted the lower the adsorption energy. Although our own N-layered integrated molecular orbital and molecular mechanics (ONIOM) calculation results indicate that isobutene hardly approaches the acid site and has a weak interaction with the zeolite framework, NBO analysis shows that it has the maximum charge transfer from the active site and the largest stabilization energy. These findings explain the reason why ZSM-5 is selective towards isobutene produced from n-butene and indicate that the acidic proton from the zeolite is easy to transfer to isobutene. Thus, further catalytic conversion of isobutene would be facile. © 2006 Elsevier B.V. All rights reserved.
  • Loading...
    Thumbnail Image
    Some of the metrics are blocked by your 
    consent settings
    Item type:Publication,
    Probing the structural and electronic factors affecting the adsorption and reactivity of alkenes in acidic zeolites using DFT calculations and multivariate statistical methods
    (2005-01-01)
    Tantanak, Duangkamol
    ;
    Limtrakul, Jumras
    ;
    Gleeson, Matthew Paul
    Quantum mechanical (QM) cluster calculations have been performed on a model of ZSM-5 at DFT and MP2 levels. We investigated how the adsorption energies and the energetics of alkoxide intermediate formation of six different alkene substrates, ethene, propene, 1-butene, cis/trans butene, and isobutene, vary in this zeolite model. An analysis of the DFT geometric, electronic, and energetic parameters of the zeolite-substrate complexes, transition states, and alkoxide intermediates is performed using principal components analysis (PCA) and partial least squares (PLS). These deliver an insight into the correlated changes that occur between molecular structure and energy along the reaction coordinate between the physisorbed and chemisorbed species within the zeolite. To the best of our knowledge, this is the first occasion multivariate techniques such as PCA or PLS have been employed to profile the changes in electronics, distances, and angles in QM calculations of catalytic systems such as zeolites. We find the calculated adsorption and the alkoxide intermediate energies correlate strongly with the absolute charge on the substrate and the length of the substrate double bond. The transition states' energies are not affected by the zeolite framework as modeled, which explains why they correlate strongly with the gas-phase substrate protonation energy. Our cluster results show that for ethene, propene, 1-butene, and isobutene, the relative energetics associated with the formation of the alkoxide intermediate in ZSM-5 follow the same trends as calculations where the effects of the framework are included. © 2005 American Chemical Society.