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    One-Pot Conversion of Furfural to γ-Valerolactone over Co- and Pt-Doped ZSM-5 Catalysts
    (2023-03-01)
    Tolek, Weerachon
    ;
    Auppahad, Warucha
    ;
    Weerachawanasak, Patcharaporn
    ;
    Mekasuwandumrong, Okorn
    ;
    Praserthdam, Piyasan
    γ-Valerolactone (GVL) is one of the useful biomass compounds produced via different reaction pathways from hemicellulose. In this study, Co- and Pt-doped/ZSM-5 catalysts with different Co loadings (0–10 wt.%) and Pt loadings (0.5–2 wt.%) were prepared by impregnation method and employed in a one-pot conversion of furfural to GVL. The yield of GVL increased with increasing reaction temperature from 100 to 140 °C. At the reaction temperature of 120 °C, higher amounts of secondary products such as AL and IPL can be converted to GVL, especially on the Co- and Pt-modified ZSM-5 catalysts. Compared to the non-modified H-ZSM-5 (GVL yield 35.4%), Co- and Pt-doped ZSM-5 catalysts exhibited much higher yield of GVL with the 1%Pt/ZSM-5 catalyst showing the highest yield of GVL at 85.4% at 120 °C and 1 bar N<inf>2</inf> without the use of liquid acid or external H<inf>2</inf> supply. The catalyst performances were correlated to the physicochemical properties of the catalysts such as the amount and type of acid sites. The NH<inf>3</inf>-TPD and in situ FTIR spectra of pyridine adsorption results revealed that Co- and Pt-loaded on ZSM-5 enhanced Lewis and weak acid sites, which are beneficial for the reaction. The results present a simple strategy to obtain high GVL yield under relatively mild conditions.
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    Application of QM simulations and multivariate analysis in the study of alkene reactivity in the zeolite H-ZSM5
    (2008-01-01)
    Gleeson, Duangkamol
    Reported herein are the results of an investigation into the effect of the extended framework of the zeolite ZSM-5 on the reaction energetics and structures of (a) the physisorbed complex formed between the zeolite and six alkenes, (b) the corresponding chemisorbed alkoxide intermediate and (c) the transition states (TS) connecting the two. For this, quantum mechanical (QM) simulations of ZSM-5 in the presence and absence of the zeolite framework have been employed. A 46T density functional theory (DFT) cluster model and a 3T:46T DFT:UFF ONIOM model are used to represent the former scenario and a simple 3T DFT cluster model for the latter. The structural implications of neglecting the zeolite framework have been rigorously compared using the multivariate statistical method principal components analysis (PCA). This method allows one to assess the correlated nature of the changes in structure along the reaction coordinate, for multiple different alkenes, in a facile, reliable way. Copyright © 2008 John Wiley & Sons, Ltd.
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    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.