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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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    Hydrogenation of CO2 to formic acid catalyzed by Co and Cu Single-atom catalysts supported on MOF-808: A DFT investigation
    (2024-12-01)
    Kusonjariyakun, Nawarat
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    Santatiwongchai, Jirapat
    ;
    Meeprasert, Jittima
    ;
    Chotpatiwetchkul, Warot
    ;
    Maihom, Thana
    In this work, DFT-based calculations and microkinetic modeling were employed to investigate CO<inf>2</inf> hydrogenation to formic acid using H<inf>2</inf> over Co and Cu single-atom catalysts supported on MOF-808. We investigated two pathways: one without the introduction of a second H<inf>2</inf> molecule (pathway A) and another one with it (pathway B). Pathway B, which involves introducing the second H<inf>2</inf> molecule alongside the formate intermediate from the first step, exhibits significantly lower energy barriers (three times lower) for the transformation into formic acid in the second step of CO<inf>2</inf> hydrogenation. Moreover, pathway B shifts the reaction thermodynamics from endergonic to exergonic, highlighting its kinetic and thermodynamic advantages. Notably, we observed formate intermediates with quasi-bidentate geometry alongside the prevalent bidentate chelating geometry. Cu<sup>2+</sup>-MOF-808 exhibits superior catalytic activity compared to Co<sup>2+</sup>-MOF-808, attributed to Cu's stronger preference for stabilizing the transition state in its square planar geometry through the Jahn-Teller effect, which is less effective in Co. Furthermore, our microkinetic modeling consistently confirms that Cu<sup>2+</sup>-MOF-808 outperforms Co<sup>2+</sup>-MOF-808 at lower temperatures, with the rate of formic acid production depending on the concentration of H<inf>2</inf>. The desorption of formic acid is identified as the rate-determining step of the reaction, significantly impacting overall efficiency.