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Author: search.filters.author.Daengngern, RathawatSubject: search.filters.subject.DFT

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    Theoretical investigation on the role of external oxygen facilitating oxidative dehydrogenation of hydrogen sulfide on Fe-based oxide catalysts
    (2025-11-15)
    Saelee, Tinnakorn
    ;
    Setasuban, Sorawee
    ;
    Noppakhun, Jakapob
    ;
    Rittiruam, Meena
    ;
    Khajondetchairit, Patcharaporn
    The oxidative dehydrogenation (ODH) of hydrogen sulfide (H<inf>2</inf>S) is a critical process in biogas purification, enabling cleaner and more efficient utilization of renewable energy sources. This study employs density functional theory (DFT) and microkinetic modeling to investigate the role of external oxygen (O<inf>ext</inf>) in enhancing the catalytic performance of O<inf>2</inf>/α-Fe<inf>2</inf>O<inf>3</inf>(0 0 0 1) surfaces. The findings reveal that O<inf>ext</inf> significantly lowers the activation energy of key reaction steps, promotes more favorable reaction pathways, and mitigates sulfur poisoning by stabilizing lattice oxygen and suppressing the formation of oxygen vacancies. The unique electronic and structural properties of the O<inf>2</inf>/α-Fe<inf>2</inf>O<inf>3</inf>(0 0 0 1) surface facilitate improved catalyst activity and extended operational stability, addressing key challenges in sustainable energy technologies. The existence of the O<inf>ext</inf> can decrease the optimal temperature of ODH of H<inf>2</inf>S from >1150 K on the pristine α-Fe<inf>2</inf>O<inf>3</inf>(0 0 0 1) surface to 850 K on the O<inf>2</inf>/α-Fe<inf>2</inf>O<inf>3</inf>(0 0 0 1) surface. Furthermore, undergoing the ODH reaction to the steady state is 1.25 × 10<sup>3</sup> times faster than that of a lean α-Fe<inf>2</inf>O<inf>3</inf>(0 0 0 1) surface. Also, the amount of poisoned species of S* on the O<inf>2</inf>/α-Fe<inf>2</inf>O<inf>3</inf>(0 0 0 1) surface is lowered significantly. This work advances the design of robust catalysts for efficient H<inf>2</inf>S removal by providing a deeper understanding of catalytic behavior and deactivation mechanisms. The insights presented here contribute to cleaner energy production and environmental protection, bridging fundamental knowledge and practical applications in catalysis.
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    Nitric oxide oxidation on warped nanographene (C80H30): a DFT study
    (2019-01-01)
    Roongcharoen, Thantip
    ;
    Kungwan, Nawee
    ;
    Daengngern, Rathawat
    ;
    Sattayanon, Chanchai
    ;
    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
    ;
    Daengngern, Rathawat
    ;
    Rungrotmongkol, Thanyada
    ;
    Jungsuttiwong, Siriporn
    ;
    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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    Heteroatom effect on photophysical properties of 2-(2′-hydroxyphenyl)benzimidazole and its derivatives as fluorescent dyes: A TD-DFT study
    (2017-08-01)
    Manojai, Natthaporn
    ;
    Daengngern, Rathawat
    ;
    Kerdpol, Khanittha
    ;
    Ngaojampa, Chanisorn
    ;
    Kungwan, Nawee
    The effects of hetero nitrogen substitution on the photophysical properties and excited-state intramolecular proton transfer (ESIPT) of HBX derivatives (HBI, HBO and HBT where X=NH, O and S, respectively) were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations at B3LYP/6-311+G(d,p) level, which is the suitable method of choice validated from various density functionals. Geometries and absorption spectra of all derivatives as well as emission spectra of selected derivatives were calculated at the same level of theory. The hetero nitrogen substitution of HBX resulted in the red shift emission spectra, which implies that the lone pair of electron in the substituted nitrogen has the effect on the π-conjugated system. In addition, results of frontier molecular orbital analysis show that vertical S<inf>0</inf>→S<inf>1</inf> transition of these molecules corresponds essentially to the excitation from HOMO (π) to LUMO (π*). The potential energy curves (PECs) of selected derivatives were used to investigate the occurrence of ESIPT and the chance was found in this order: HBT>HBI>HBO. The hetero nitrogen substituted on 1,4 and 3,4 position of HBX derivatives could easily facilitate the ESIPT process, because the nitrogen substitution makes O–H bond of selected HBX derivatives weaker than those of other derivatives and the hydrogen bond in N–H becomes stronger in the excited state, resulting in lower PT barrier. The obtained information of the electronic structure, the photophysical property and the chance of ESIPT of hetero nitrogen substituted HBX molecules is useful for molecular design of fluorescent molecular probes.