Daengngern, Rathawat

Preferred name

Alternative Name

Daengngern, R.

Main Affiliation

School of Science

rathawat.da@kmitl.ac.th

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Excited-state intramolecular proton transfer reactions of 2,5-bis(2′-benzoxazolyl)hydroquinone and its water cluster exhibiting single and double proton transfer: A TD-DFT dynamics simulation
(2019-07-15)
Daengngern, Rathawat
;
Salaeh, Rusrina
;
Saelee, Tinnakorn
;
Kerdpol, Khanittha
;
Kungwan, Nawee
Detailed pictures of the excited-state intramolecular proton transfer (ESIPT)of 2,5-bis(2′-benzoxazolyl)hydroquinone (BHQ)and its water cluster have been investigated by dynamics simulations on the first lowest-excited energy using time-dependent density functional theory (TD-DFT). We focused on the structural, photophysical and dynamic properties of BHQ in the absence and presence of water molecules through intermolecular hydrogen bonds (interHBs). Our dynamics simulations reveal three possible mechanisms of the ESIPT processes: i)no proton transfer (No PT); ii)single PT (SPT); and iii)double PT (DPT), that could take place within the PT time of 160 fs via intrinsic intramolecular hydrogen bonds (intraHBs). The ESIPT mechanism of isolated BHQ elucidates that back PT is likely to be found at 64% rather than the SPT (32%)and DPT (4%), which is in good agreement with the experiments of dual fluorescence from di-enol and mono-keto emissions. Notably, the results from BHQ with water (BHQ-(H<inf>2</inf>O)<inf>2</inf>)reveal that the participation of water might produce a remarkable effect on promoting the SPT process up to 60% and DPT up to 7 times when compared to conditions of no water. The simulated probability of PT is well related to possible PT mechanisms regarding different tautomers in the fluorescence spectra found in previous experiments. The existence of di-keto tautomer arose from the DPT of BHQ and its water cluster and was not observed in the UV/Vis spectrum.
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A theoretical investigation into the demethylation mechanism of dimethylsulfide over the W3O6 cluster
(2025-07-01)
Aziz, Hafiz Aji
;
Kungwan, Nawee
;
Gleeson, Duangkamol
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Saelee, Tinnakorn
;
Daengngern, Rathawat
Understanding how dimethyl sulfide (DMS) breaks down to form value-added products such as methanol on transition metal oxide catalysts is important for improving desulfurization processes. In this study, the reaction mechanism over a tungsten oxide cluster (W₃O₆) is elucidated using density functional theory (DFT) at the M06-L/LANL2DZ/aug-cc-pVTZ level of theory. Two competing mechanistic pathways were discovered over the W₃O₆ cluster: Pathway A) direct demethylation followed by methanol desorption and Pathway B) a water-assisted concerted demethylation pathway. Pathway A involves sequential steps with a moderate demethylation barrier (49.43 kcal/mol), but a significantly higher barrier (68.78 kcal/mol) for subsequent methanol formation, imposing a kinetic bottleneck. Remarkably, Pathway B, mediated by an explicit water molecule, facilitates a lower-barrier concerted transformation (56.19 kcal/mol), effectively bypassing the high-energy intermediate. Kinetic modeling via Transition State Theory and the Energetic Span Model reveal that despite the very low turnover frequency (TOF = 9.29 × 10<sup>−30</sup> s⁻¹), the water-assisted pathway is energetically superior. These findings highlight the important role of water in helping the reaction proceed and offer insight for designing better catalysts for sulfur removal from DMS to methanol over the W₃O₆ cluster.
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Bridging the Gap in Understanding the Mechanism of NH3 Formation During NO Reduction by CO in the Presence of H2O Over Rh/Al2O3 Catalysts: DFT Study
(2026-02-01)
Wangphon, Chanthip
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Khajondetchairit, Patcharaporn
;
Rittiruam, Meena
;
Ektarawong, Annop
;
Alling, Björn
Ammonia (NH<inf>3</inf>) formation from nitric oxide (NO) and carbon monoxide (CO) in the presence of water is a promising pathway for low-temperature NO<inf>x</inf> reduction. In this work, density functional theory (DFT) calculations were used to investigate the mechanism of NH<inf>3</inf> formation on a Rh(111)/γ-Al<inf>2</inf>O<inf>3</inf>(110), in which the Rh(111) and γ-Al<inf>2</inf>O<inf>3</inf>(110) were considered separately. NO readily dissociates on the Rh site, forming N*, which reacts with CO to produce the key intermediate of NCO*. Meanwhile, water dissociates more easily on γ-Al<inf>2</inf>O<inf>3</inf>(110), providing H* species. The hydrolysis of NCO* can proceed via two pathways: on Rh(111), it forms HNCO, while on γ-Al<inf>2</inf>O<inf>3</inf>(110), it forms HNCOH*. Both intermediates subsequently decompose into NH* species, which are then hydrogenated to produce NH<inf>3</inf>. The Rh pathway is more favorable in both kinetics and thermodynamics, while the support mainly supplies hydrogen through water activation. These results suggest a dual-site mechanism in which Rh drives the main transformation, and γ-Al<inf>2</inf>O<inf>3</inf>(110) assists via hydrogen transfer. This work presents the individual roles of Rh and Al<inf>2</inf>O<inf>3</inf> surfaces in NO reduction with CO, producing NH<inf>3</inf>, which is relevant to catalytic behavior under humid conditions.
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First-Principles Screening of 3d-Transition-Metal-Doped Hydrous Cobalt Phosphate Catalysts for Enhanced Oxygen Evolution Reaction
(2025-09-01)
Rittiruam, Meena
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Saelee, Tinnakorn
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Khajondetchairit, Patcharaporn
;
Ektarawong, Annop
;
Alling, Björn
Hydrous cobalt phosphate (CoPO) is a promising OER catalyst, but its activity is limited by poor electron transport and weak intermediate binding. This study reveals how 3d transition metal dopants can be used to tune these properties through first-principles calculations. Sc, Ti, V, and Cr improve catalytic activity by promoting electron transfer and stabilizing *O intermediates, while Mn, Fe, Cu, and Zn reduce performance. Among all candidates, Ni doping strikes the optimal balance, enhancing conductivity and providing moderate *O binding energy that minimizes overpotential. These trends follow electronic descriptors such as d-band center and electronegativity, and are validated by volcano plot analysis. Ni-CoPO emerges as the most effective design, offering a clear strategy for improving OER catalysts by controlling dopant identity and electronic structure.
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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
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Setasuban, Sorawee
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Noppakhun, Jakapob
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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.

Daengngern, Rathawat

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