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Tailoring the First Coordination Shell of Isolated Ti(IV) Active Sites in Zeolite Frameworks Boosting Catalytic Activity in Epoxidation
(2025-05-08)
Klinyod, Sorasak
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Yomthong, Krissanapat
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Suttipat, Duangkamon
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Pornsetmetakul, Peerapol
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Kidkhunthod, Pinit
We present a strategy to precisely tune the local structure of the tetrahedrally coordinated titanium (Ti) sites incorporated in the zeolite framework via a one-pot hydrothermal synthesis with the aid of NH<inf>4</inf>F without any further postmodification step. This approach effectively prevents typical issues observed in postsynthetic methods, such as Ti leaching and zeolite framework degradation. By optimizing the NH<inf>4</inf>F concentration in the synthesis precursor, the formation of open Ti(OSi)<inf>3</inf>OH and Ti(OSi)<inf>3</inf>F active species can be precisely controlled. To elucidate the relationship between various Ti active species, including closed Ti(OSi)<inf>4</inf>, open Ti(OSi)<inf>3</inf>OH, and open Ti(OSi)<inf>3</inf>F sites and their catalytic performances in methyl oleate (MO) epoxidation, we employed ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), fluorine X-ray absorption near edge structure spectroscopy (F-XANES), and density functional theory (DFT) calculations. Our findings reveal that increased positive charges on Ti active centers, in the order of closed Ti(OSi)<inf>4</inf> < open Ti(OSi)<inf>3</inf>OH < open Ti(OSi)<inf>3</inf>F, correlate with enhanced catalytic performance in MO epoxidation. However, an excessive proportion of Ti(OSi)<inf>3</inf>F species in the framework can diminish catalytic performance by promoting undesired side reactions. Therefore, we propose an optimized balance between open Ti(OSi)<inf>3</inf>OH and open Ti(OSi)<inf>3</inf>F species in the zeolite structure to maximize the catalytic activity of epoxidation.
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Effect of water microsolvation on the excited-state proton transfer of 3-hydroxyflavone enclosed in -cyclodextrin
(2021-02-02)
Kerdpol, Khanittha
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Daengngern, Rathawat
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Sattayanon, Chanchai
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Namuangruk, Supawadee
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Rungrotmongkol, Thanyada
The effect of microsolvation on excited-state proton transfer (ESPT) reaction of 3-hydroxyflavone (3HF) and its inclusion complex with -cyclodextrin (-CD) was studied using computational approaches. From molecular dynamics simulations, two possible inclusion complexes formed by the chromone ring (C-ring, Form I) and the phenyl ring (P-ring, Form II) of 3HF insertion to -CD were observed. Form II is likely more stable because of lower fluctuation of 3HF inside the hydrophobic cavity and lower water accessibility to the encapsulated 3HF. Next, the conformation analysis of these models in the ground (S0) and the first excited (S1) states was carried out by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, respectively, to reveal the photophysical properties of 3HF influenced by the -CD. The results show that the intermolecular hydrogen bonding (interHB) between 3HF and -CD, and intramolecular hydrogen bonding (intraHB) within 3HF are strengthened in the S1 state confirmed by the shorter interHB and intraHB distances and the red-shift of O-H vibrational modes involving in the ESPT process. The simulated absorption and emission spectra are in good agreement with the experimental data. Significantly, in the S1 state, the keto form of 3HF is stabilized by -CD, explaining the increased quantum yield of keto emission of 3HF when complexing with -CD in the experiment. In the other word, ESPT of 3HF is more favorable in the -CD hydrophobic cavity than in aqueous solution.
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Nitric oxide oxidation on warped nanographene (C80H30): a DFT study
(2019-01-01)
Roongcharoen, Thantip
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Kungwan, Nawee
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Daengngern, Rathawat
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Sattayanon, Chanchai
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Namuangruk, Supawadee
The possible use of the recently synthesized warped nanographene C<inf>80</inf>H<inf>30</inf> for NO oxidation by O<inf>2</inf> molecule has been investigated using density functional theory. The reaction starts with the adsorption and dissociation of O<inf>2</inf> molecule on the central pentagon of C<inf>80</inf>H<inf>30</inf> with the activation energies of 24.2–26.6 kcal/mol depending on the active sites. Then, the dissociated O atoms readily oxidize NO to NO<inf>2</inf> twice. The first NO oxidation occurs with barrierless, while the second NO oxidation requires a small energy barrier of 16.0 kcal/mol. The low activation energy barrier pathway indicates high catalytic activity of this nanographene for NO oxidation. Charge analysis reveals that such high catalytic activity of nanographene is attributed to the charge transfer from the saddle-shaped C<inf>80</inf>H<inf>30</inf> to the dissociated O atoms which makes it reactive to NO molecule. Desorption of NO<inf>2</inf> product, which is the rate-limiting step of NO oxidation in some catalysts, is easily occurred in this nanographene (less than 2 kcal/mol), indicating the prevention of catalyst poisoning. This study suggests that C<inf>80</inf>H<inf>30</inf> nanographene is a promising catalyst for NO removal in ambient condition.
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A spectroscopic study of indigo dye in aqueous solution: A combined experimental and TD-DFT study
(2018-12-01)
Jiwalak, Naparat
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Daengngern, Rathawat
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Rungrotmongkol, Thanyada
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Jungsuttiwong, Siriporn
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Namuangruk, Supawadee
This study reports UV–Visible spectra and electronic structures of indigo (IG) in aqueous solution using a combination of experimental and theoretical methods. In the visible region, the experimental absorption spectrum of the solution showed a broad peak with the longest wavelength of maximal absorption (λ<inf>max</inf>) value at 708 nm. For the theoretical method, a trans-IG monomer and a trans-IG bound with two water molecules (IG.2W) were optimized in the ground state using the B3LYP and B3LYP-D3 calculations with the 6-31 + G(d,p) basis set and the SCRF-CPCM model for taking solvent effect into account was also applied. Sequentially, the UV–Visible spectra and λ<inf>max</inf> of the optimized trans-IG and IG.2W models in the implicit water were simulated by the time-dependent density functional theory (TD-DFT) calculations. The TD-DFT methods including BLYP, B3LYP, PBE0, CAM-B3LYP, M06-2X, ωB97XD, LC-BLYP, and LC-ωPBE functionals without and with the D3 correction and the 6-31 + G(d,p) basis set were selected. The results pointed out that BLYP and BLYP-D3 were the best methods because they could reproduce the experimental λ<inf>max</inf> value of IG in aqueous solution. The predicted λ<inf>max</inf> values of IG.2W were almost equal to 708 nm (the experimental data), indicating that IG.2W could be responsible for optical properties of IG.
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Oxotitanium-porphyrin for selective catalytic reduction of NO by NH3: A theoretical mechanism study
(2018-01-01)
Daengngern, Rathawat
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Maitarad, Phornphimon
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Shi, Liyi
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Zhang, Dengsong
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Kungwan, Nawee
The reaction mechanism of the selective catalytic reduction of NO by NH<inf>3</inf> (NH<inf>3</inf>-SCR) on an oxotitanium-porphyrin catalyst was systematically investigated by using density functional theory calculations with the M06L functional. The reaction was proposed to follow the nitrite mechanism over the two forms of active sites; the oxotitanium-porphyrin Lewis acid site (TiO-por) and the Brønsted acid site (TiOH-por). The reaction path consisted of (i) nitrite formation, (ii) NH<inf>3</inf> oxidation, (iii) formation of NH<inf>2</inf>NO and NHNOH intermediates, and (iv) N<inf>2</inf> and H<inf>2</inf>O product formation. The obtained calculations showed that the formation of the NHNOH intermediate was the rate determining step for both active sites with the energy barriers (E<inf>a</inf>) of 32.2 and 36.2 kcal mol<sup>-1</sup> for the Lewis and Brønsted acid sites, respectively. It is worth noting that the activation energy for NHNOH formation over the oxotitanium-porphyrin active sites was found to be in the same range as that of vanadium oxide cluster models. Furthermore, the product formations of N<inf>2</inf> and H<inf>2</inf>O over the Lewis and Brønsted acid sites of oxotitanium-porphyrin were exothermic processes with reaction energies (E<inf>r</inf>) of -67.1 and -39.0 kcal mol<sup>-1</sup>, respectively. Thus, in conclusion, the oxotitanium-porphyrin could theoretically act as an alternative catalyst for NH<inf>3</inf>-SCR of NO and it would be challenging to test it in experimental studies.
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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
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Tantanak, Duangkamol
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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.

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