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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
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Meeprasert, Jittima
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Chotpatiwetchkul, Warot
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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. Cu2+-MOF-808 exhibits superior catalytic activity compared to Co2+-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 Cu2+-MOF-808 outperforms Co2+-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.
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Effects of zeolite frameworks and hierarchical structures on catalytic bioethanol dehydration: In-situ DRIFTS and DFT studies
(2023-04-15)
Iadrat, Ploychanok
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Yomthong, Krissanapat
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Rodaum, Chadatip
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Pornsetmetakul, Peerapol
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Thivasasith, Anawat
Herein, the combined in-situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory studies were employed to investigate the effects of different zeolite frameworks and hierarchical structures on catalytic bioethanol dehydration. The findings reveal that different zeolite frameworks enable the formation of distinct intermediates, hence promoting different mechanistic pathways. Interestingly, the FER is highly selective to ethylene and inhibits the formation of by-products thanks to the confined porous structure of the FER. Although the pristine small pore FER often suffers from fast catalyst deactivation, the incorporation of hierarchical structures in the FER framework can mitigate this significantly. Accordingly, the catalytic stability of the hierarchical FER was improved remarkably with a high ethylene yield (∼95%), whereas the pristine FER suffers from fast deactivation. Additionally, coke formation over the hierarchical FER catalyst was also reduced significantly compared to that of the pristine FER. Importantly, the in-situ DRIFTS studies reveal that the different reaction pathways over hierarchical and commercial FER have been observed in which the hierarchical one promotes the monomeric pathway due to the facile desorption of corresponding products and intermediates, whilst the pristine one promotes bioethanol conversion via both pathways of monomeric and dimeric pathways to produce ethylene and diethyl ether, respectively.
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Direct conversion of carboxylic acid to olefins over Pt-loaded, oxygen-deficient alkali hexatitanate catalysts with ketonization-hydrogenation-dehydration activity
(2021-09-01)
Promchana, Pratya
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Boonchun, Adisak
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T-Thienprasert, Jiraroj
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Sooknoi, Tawan
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Maluangnont, Tosapol
The production of long chain olefins from fatty acids via decarbonylation is limited by low olefins selectivity at high conversion. Here, we reported the direct acid-to-olefins conversion via the ketonization-hydrogenation-dehydration sequence at 400 °C and atmospheric 10 %H<inf>2</inf>/Ar. The oxygen vacancy defects (V<inf>O</inf>) were essential in acetic acid ketonization over the oxygen-deficient alkali hexatitanate A<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> (A[dbnd]K, Na and Li) catalysts, as evidenced from the activity of reduced vs non-reduced catalysts. The presence of V<inf>O</inf> was deduced spectroscopically with XPS and DRUV-VIS, and the ease of V<inf>O</inf> formation was ranked via the DFT calculations. The ketonization activity was proportionated to the square of the V<inf>O</inf> content (x2), consistent with the bimolecular reaction mechanism. The Pt-loaded K<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> enabled the direct acid-to-olefins transformation as shown by a complete conversion of two model compounds (heptanoic acid and lauric acid) with ∼30–40 % yield of long chain olefins. Heptanoic acid (C<inf>7</inf>) underwent ketonization to 7-tridecanone (a C<inf>13</inf> ketone) prior to the hydrogenation-dehydration to 7-tridecene, a C<inf>13</inf> olefin. The strong metal-support interaction (SMSI) between Pt and K<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> inhibited further hydrogenation of the olefin to a low-value alkane. For lauric acid (C<inf>12</inf>), 12-tricosene (a C<inf>23</inf> olefin) was produced analogously. The catalytic activity and products selectivity over Pt-loaded K<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> significantly depended on the Pt content (0–1.0 wt%). The simultaneous C[sbnd]C coupling and oxygen removal prior to the subsequent hydrogenation and dehydration is a potential approach toward the production of long chain olefins with the (2n-1) carbon atoms from C<inf>n</inf>-fatty acids.
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Theoretical investigation of rhodamine6g derivative as fluorescence metal ion sensor
(2014-07-24)
Puingam, R.
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Chindaduang, A.
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Tumcharern, G.
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Sae-Tang Phromyothin, D.
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Pratontep, S.
The structural, energetic and optical properties of a Rhodamine6G derivative as the fluoroionphore for metal ion detection, particularly mercury, have been investigated using the time-dependent density functional theory (TD-DFT), compared to experiments. The TD-DFT calculations with the B3LYP method were conducted in the absence and the presence of metal ions. The results indicate that the absorption peaks of the pristine molecules are located at 236 and 282 nm, whereas the selective Hg2+ binding peaks emerge at 263, 371 and 551 nm. A distinctive new band emerges around 550 nm, in accordance with the experiments, attributed to the metal-to-ionophore electron transfer. © 2014 Taylor & Francis Group, LLC.
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Efficeincy improvement of triphenylamine-based organic dyes in DSSCs, an effects of linker moiety
(2013-10-29)
Chittratan, P.
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Thanakit, P.
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Jarernboon, W.
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Phromyothin, D.
Triphenylamine-base organic dyes were designed and investigated for dye-sensitized solar cells (DSSCs). The dye molecules consist of three parts, an electron-donor connected by the π- conjugated linker (benzene and thiophene) as an electron spacer and an acceptor/anchoring (cyanoacrylic acid). In this study, quantum chemical calculations were used to study the electronic properties, optical properties and density of electron in the linker of dye molecule by using the density functional theory. The results present that thiophene is the most appropriate to use as electron linker between triphenylamine donor and acrylic acceptor due to the wide of absorption band and π-conjugate bond effect on exhibiting red-shifted absorption spectra. © (2013) Trans Tech Publications, Switzerland.

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