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Author: search.filters.author.Bureekaew, SareeyaHas files: No

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    CO2photoreduction on mixed Ti/Zr-MOF-525: bicarbonate as the active intermediate and the role of Ti substitution
    (2026-02-11)
    Puengpoka, Thanyaporn
    ;
    Santatiwongchai, Jirapat
    ;
    Chotpatiwetchkul, Warot
    ;
    Bureekaew, Sareeya
    ;
    Saleh, Muhammad
    The photocatalytic reduction of CO<inf>2</inf> in metal–organic frameworks (MOFs) offers a sustainable route to C<inf>1</inf> fuels and chemicals. Herein, density functional theory (DFT) calculations elucidate CO<inf>2</inf> reduction on mixed Ti/Zr-MOF-525 clusters bearing missing linker defects, modeled by Zr<inf>6</inf>, Ti<inf>1</inf>Zr<inf>5</inf>, and Ti<inf>2</inf>Zr<inf>4</inf> clusters. Two distinct mechanistic pathways are identified: the OH-passive and OH-assisted routes. In the passive case, CO<inf>2</inf> binds weakly at a coordinatively unsaturated Ti/Zr site and undergoes direct hydrogenation to CO and HCOOH, with desorption being thermodynamically preferred over further hydrogenation. In contrast, the OH-assisted pathway proceeds via a bicarbonate-mediated mechanism, where surface –OH attacks adsorbed CO<inf>2</inf> to form node-bound *HCO<inf>3</inf>. This step is both thermodynamically favorable and kinetically accessible (ΔG<sup>‡</sup> < 0.5 eV). Subsequent proton-electron additions convert *HCO<inf>3</inf> to *OCHO and H<inf>2</inf>O, favored by ∼1 eV over competing routes. These findings identify *HCO<inf>3</inf> as the true reactive precursor and reveal that Ti substitution promotes deeper hydrogenation beyond two-electron products, enhancing CH<inf>4</inf> formation on the Ti<inf>2</inf>Zr<inf>4</inf> cluster. Overall, the results highlight the importance of node composition and surface hydroxyl groups in porphyrinic MOFs for optimizing multi-electron CO<inf>2</inf> reduction and controlling product selectivity by tailoring the metal node environments.
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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
    ;
    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.