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| 2. |
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| 3. |
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| 4. |
- Ambre, Ram B., et al.
(författare)
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Molecular engineering for efficient and selective iron porphyrin catalysts for electrochemical reduction of CO2 to CO
- 2016
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Ingår i: CHEMICAL COMMUNICATIONS. - : Royal Society of Chemistry. - 1359-7345 .- 1364-548X. ; 52:100, s. 14478-14481
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Tidskriftsartikel (refereegranskat)abstract
- Iron porphyrins Fe-pE, Fe-mE, and Fe-oE were synthesized and their electrochemical behavior for CO2 reduction to CO has been investigated. The controlled potential electrolysis of Fe-mE gave exclusive 65% Faradaic efficiency (FE) whereas Fe-oE achieved quasi-quantitative 98% FE (2% H-2) for CO production.
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| 5. |
- Biaobiao, Zhang, et al.
(författare)
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Modifying Ru-bda Backbone with Steric Hindrance and Hydrophilicity: Influence of Secondary Coordination Environments on Water-Oxidation Mechanism.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the seven coordination and O−O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earth-abundant metals. This work reports the synthesis, characterization and catalytic properties of a monomeric ruthenium catalyst Ru-bnda (H2bnda = 2,2'-bi(nicotinic acid)-6,6'-dicarboxylic acid) featuring steric hindrance and enhanced hydrophilicity on the backbone. Combining experimental evidence with systematic density functional theory calculations on the Ru-bnda and related catalysts Ru-bda, Ru-pda and Ru-biqa, we emphasized that seven coordination clearly determines presence of RuV=O with high spin density on the ORuV=O atom, i.e. oxo with radical properties, which is one of the necessary conditions for reacting through the O−O coupling pathway. However, an additional factor to make the condition sufficient is the favorable intermolecular face-to-face interaction for the generation of the pre-reactive [RuV=O···O=RuV], which is significantly influenced by the secondary coordination environments. This work provides a new understanding of the structure-activity relationship of water-oxidation catalysts and their potential to adopt I2M pathway for O−O bond formation.
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| 6. |
- Daniel, Quentin, et al.
(författare)
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Rearranging from 6-to 7-coordination initiates the catalytic activity : An EPR study on a Ru-bda water oxidation catalyst
- 2017
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Ingår i: Coordination chemistry reviews. - : Elsevier. - 0010-8545 .- 1873-3840. ; 346, s. 206-215
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Tidskriftsartikel (refereegranskat)abstract
- The coordination of a substrate water molecule on a metal centered catalyst for water oxidation is a crucial step involving the reorganization of the ligand sphere. This process can occur by substituting a coordinated ligand with a water molecule or via a direct coordination of water onto an open site. In 2009, we reported an efficient ruthenium-based molecular catalyst, Ru-bda, for water oxidation. Despite the impressive improvement in catalytic activity of this type of catalyst over the past years, a lack of understanding of the water coordination still remains. Herein, we report our EPR and DFT studies on Ru-bda (triethylammonium 3-pyridine sulfonate)(2) (1) at its Ru-III oxidation state, which is the initial state in the catalytic cycle for the O-O bond formation. Our investigation suggests that at this III-state, there is already a rearrangement in the ligand sphere where the coordination of a water molecule at the 7th position (open site) takes place under acidic conditions (pH = 1.0) to form a rare 7-coordinated Ru-III species.
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| 7. |
- Daniel, Quentin, et al.
(författare)
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Water Oxidation Initiated by In Situ Dimerization of the Molecular Ru(pdc) Catalyst
- 2018
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Ingår i: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435 .- 2155-5435. ; 8:5, s. 4375-4382
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Tidskriftsartikel (refereegranskat)abstract
- The mononuclear ruthenium complex [Ru(pdc)L-3] (H(2)pdc = 2,6-pyridinedicarboxylic acid, L = N-heterocycles such as 4-picoline) has previously shown promising catalytic efficiency toward water oxidation, both in homogeneous solutions and anchored on electrode surfaces. However, the detailed water oxidation mechanism catalyzed by this type of complex has remained unclear. In order to deepen understanding of this type of catalyst, in the present study, [Ru(pdc)(py)(3)] (py = pyridine) has been synthesized, and the detailed catalytic mechanism has been studied by electrochemistry, UV-vis, NMR, MS, and X-ray crystallography. Interestingly, it was found that once having reached the Ru-IV state, this complex promptly formed a stable ruthenium dimer [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(2)](+). Further investigations suggested that the present dimer, after one pyridine ligand exchange with water to form [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(H2O)](+), was the true active species to catalyze water oxidation in homogeneous solutions.
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| 8. |
- Duan, Lele, et al.
(författare)
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Highly efficient and robust molecular ruthenium catalysts for water oxidation
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:39, s. 15584-15588
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Tidskriftsartikel (refereegranskat)abstract
- Water oxidation catalysts are essential components of light-driven water splitting systems, which could convert water to H-2 driven by solar radiation (H2O + h nu -> 1/2O(2) + H-2). The oxidation of water (H2O -> 1/2O(2) + 2H(+) + 2e(-)) provides protons and electrons for the production of dihydrogen (2H(+) + 2e(-) -> H-2), a clean-burning and high-capacity energy carrier. One of the obstacles now is the lack of effective and robust water oxidation catalysts. Aiming at developing robust molecular Ru-bda (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) water oxidation catalysts, we carried out density functional theory studies, correlated the robustness of catalysts against hydration with the highest occupied molecular orbital levels of a set of ligands, and successfully directed the synthesis of robust Ru-bda water oxidation catalysts. A series of mononuclear ruthenium complexes [Ru(bda)L-2] (L = pyridazine, pyrimidine, and phthalazine) were subsequently synthesized and shown to effectively catalyze Ce-IV-driven [Ce-IV = Ce(NH4)(2()NO3)(6)] water oxidation with high oxygen production rates up to 286 s(-1) and high turnover numbers up to 55,400.
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| 9. |
- Fan, Ting, et al.
(författare)
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The Ru-tpc Water Oxidation Catalyst and Beyond : Water Nucleophilic Attack Pathway versus Radical Coupling Pathway.
- 2017
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Ingår i: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435 .- 2155-5435. ; 7:4, s. 2956-2966
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Tidskriftsartikel (refereegranskat)abstract
- Many Ru water oxidation catalysts have been documented in the literature. However, only a few can catalyze the O-O bond formation via the radical coupling pathway, while most go through the water nucleophilic attack pathway. Understanding the electronic effect on the reaction pathway is of importance in design of active water oxidation catalysts. The Ru-bda (bda = 2,2'-bipyridine-6,6'-dicarboxylate) catalyst is one example that catalyzes the 0-0 bond formation via the radical coupling pathway. Herein, we manipulate the equatorial backbone ligand, change the doubly charged bda(2-) ligand to a singly charged tpc- (2,2':6',2 ''-terpyridine-6-carboxylate) ligand, and study the structure activity relationship. Surprisingly, kinetics measurements revealed that the resulting Ru-tpc catalyst catalyzes water oxidation via the water nucleophilic attack pathway, which is different from the Ru-bda catalyst. The O-O bond formation Gibbs free energy of activation (AGO) at T = 298.15 K was 20.2 +/- 1.7 kcal mol(-1). The electronic structures of a series of Ru-v=O species were studied by density function theory calculations, revealing that the spin density of O-Ru=O of Ru-v=O is largely dependent on the surrounding ligands. Seven coordination configuration significantly enhances the radical character of Ru-v=O.
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| 10. |
- Staehle, Robert, et al.
(författare)
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Water oxidation catalyzed by mononuclear ruthenium complexes with a 2,2′-bipyridine-6,6′-dicarboxylate (bda) ligand : How ligand environment influences the catalytic behavior
- 2014
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 53:3, s. 1307-1319
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Tidskriftsartikel (refereegranskat)abstract
- A new water oxidation catalyst [RuIII(bda)(mmi)(OH 2)](CF3SO3) (2, H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid; mmi = 1,3- dimethylimidazolium-2-ylidene) containing an axial N-heterocyclic carbene ligand and one aqua ligand was synthesized and fully characterized. The kinetics of catalytic water oxidation by 2 were measured using stopped-flow technique, and key intermediates in the catalytic cycle were probed by density functional theory calculations. While analogous Ru-bda water oxidation catalysts [Ru(bda)L2] (L = pyridyl ligands) are supposed to catalyze water oxidation through a bimolecular coupling pathway, our study points out that 2, surprisingly, undergoes a single-site water nucleophilic attack (acid-base) pathway. The diversion of catalytic mechanisms is mainly ascribed to the different ligand environments, from nonaqua ligands to an aqua ligand. Findings in this work provide some critical proof for our previous hypothesis about how alternation of ancillary ligands of water oxidation catalysts influences their catalytic efficiency.
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| 11. |
- Tong, Lianpeng, et al.
(författare)
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Water Oxidation Catalysis : Influence of Anionic Ligands upon the Redox Properties and Catalytic Performance of Mononuclear Ruthenium Complexes
- 2012
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 51:6, s. 3388-3398
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Tidskriftsartikel (refereegranskat)abstract
- Aiming at highly efficient molecular catalyts for water oxidation, a mononuclear ruthenium complex Ru-II(hqc)(pic)(3) (1; H(2)hqc = 8-hydroxyquinoline-2-carboxylic acid and plc = 4-picoline) containing negatively charged carboxylate and phenolate donor groups has been designed and synthesized. As a comparison, two reference complexes, Ru-II(pdc)(pic)(3) (2; H(2)pdc = 2,6-pyridine-dicarboxylic acid) and Ru-II(tpy)(pic)(3) (3; tpy = 2,2':6',2 ''-terpyridine), have also been prepared. All three complexes are fully characterized by NMR, mass spectrometry (MS), and X-ray crystallography. Complex 1 showed a high efficiency toward catalytic water oxidation either driven by chemical oxidant (Ce-IV in a pH 1 solution) with a initial turnover number of 0.32 s(-1), which is several orders of magnitude higher than that of related mononuclear ruthenium catalysts reported in the literature, or driven by visible light in a three-component system with [Ru(bpy)(3)](2+) types of photosensitizers. Electrospray ionization MS results revealed that at the Rum state complex 1 undergoes ligand exchange of 4-picoline with water, forming the authentic water oxidation catalyst in situ. Density functional theory (DFT) was ernployed to explain how anionic ligands (hqc and pdc) facilitate the 4-picoline dissociation compared with a neutral ligand (tpy). Electrochemical measurements show that complex 1 has a much lower E(Ru-III/Ru-II) than that of reference complex 2 because of the introduction of a phenolate ligand. DFT was further used to study the influence of anionic ligands upon the redox properties of mononuclear aquaruthenium species, which are postulated to be involved in the catalysis cycle of water oxidation.
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| 12. |
- Wang, Ying, et al.
(författare)
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Alkene Epoxidation Catalysts [Ru(pdc)(tpy)] and [Ru(pdc)(pybox)] Revisited : Revealing a Unique Ru-IV=O Structure from a Dimethyl Sulfoxide Coordinating Complex
- 2015
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435 .- 2155-5435. ; 5:7, s. 3966-3972
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Tidskriftsartikel (refereegranskat)abstract
- The X-ray crystal structure of a dimethyl sulfoxide (DMSO) coordinating complex [Ru-II(kappa(2)-pdc)(tpy)(DMSO)] (H(2)pdc = 2,6-pyridyl dicarboxylic acid and tpy = 2,2':6',2 ''-terpyridine) led to the discovery of a unique Ru-IV=O configuration for the Ru-pybox (pybox = pyridine-bis(oxazoline) ligands) epoxidation catalyst by theoretical calculations. On the basis of this structure, a detailed theoretical study was conducted on the alkene epoxidation reaction using ruthenium-based epoxidation catalysts. It was found that the process of H2O2 coordination proceeded via an associative path in which one carboxylate detached. The following H2O-elimination step was found to be facilitated by the detached carboxylate group. The resulting Ru-IV=O rearranges to the species trans-2a-oxo, in which one carboxylate group is situated over the tpy ring; the trans-2a-oxo was found to have the lowest activation free energies toward alkene epoxidation. These results demonstrated the importance of the hemilabile properties of the pdc(2-) ligand for the Ru-pdc alkene epoxidation catalysts.
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| 13. |
- Wu, G. J., et al.
(författare)
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Effects of Initial Shear Layer State on Screech in a RectangulaJet
- 2022
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Ingår i: 28th AIAA/CEAS Aeroacoustics Conference, 2022. - Reston, Virginia : American Institute of Aeronautics and Astronautics (AIAA).
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Konferensbidrag (refereegranskat)abstract
- High-fidelity large-eddy simulations are conducted for a 4:1 rectangular supersonic nozzle at under-expanded screeching conditions. By creating a small groove on the nozzle surface, we numerically modify the boundary layer inside the nozzle and the resulting jet initial shear layer. A total of 5 cases with different groove sizes are studied and compared with the no-groove baseline case. Near-field flow statistics and far-field acoustics are analyzed. The geometric tripping method is shown to increase the turbulent kinetic energy and boundary layer thickness at the nozzle exit. The slight modification in the initial shear layer state leads to different shear layer thicknesses and shock cell decay rates near the end of the jet potential core. Screech tone amplitude variation is observed, with largest difference measured to be 2.9 dB compared to the baseline value. The dominant coherent structures associated with screech generation are studied with spectral proper orthogonal decomposition. The amplitudes of the internal upstream-traveling wave and the downstream-traveling Kelvin-Helmholtz wave are calculated. The differences in the screech tone amplitude are found to be related to the strength of the Kelvin-Helmholtz wave, which is a result of the modified receptivity of the initial shear layer.
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| 14. |
- Yang, Jing, et al.
(författare)
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From Ru-bda to Ru-bds : a step forward to highly efficient molecular water oxidation electrocatalysts under acidic and neutral conditions
- 2021
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Significant advances during the past decades in the design and studies of Ru complexes with polypyridine ligands have led to the great development of molecular water oxidation catalysts and understanding on the O-O bond formation mechanisms. Here we report a Ru-based molecular water oxidation catalyst [Ru(bds)(pic)(2)] (Ru-bds; bds(2-) = 2,2-bipyridine-6,6 ' -disulfonate) containing a tetradentate, dianionic sulfonate ligand at the equatorial position and two 4-picoline ligands at the axial positions. This Ru-bds catalyst electrochemically catalyzes water oxidation with turnover frequencies (TOF) of 160 and 12,900s(-1) under acidic and neutral conditions respectively, showing much better performance than the state-of-art Ru-bda catalyst. Density functional theory calculations reveal that (i) under acidic conditions, the high valent Ru intermediate Ru-V=O featuring the 7-coordination configuration is involved in the O-O bond formation step; (ii) under neutral conditions, the seven-coordinate Ru-IV=O triggers the O-O bond formation; (iii) in both cases, the I2M (interaction of two M-O units) pathway is dominant over the WNA (water nucleophilic attack) pathway. Developing efficient molecular water oxidation catalysts for artificial photosynthesis is a challenging task. Here the authors introduce a ruthenium based complex with negatively charged sulfonate groups to effectively drive water oxidation under both acidic and neutral conditions.
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| 15. |
- Zhang, Biaobiao, et al.
(författare)
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Modifying Ru-bda Backbone with Steric Hindrance and Hydrophilicity: Influence of Secondary Coordination Environments on Water-Oxidation Mechanism
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the seven coordination and O-O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earth-abundant metals. This work reports the synthesis, characterization and catalytic properties of a monomeric ruthenium catalyst Ru-bnda (H2bnda = 2,2'-bi(nicotinic acid)-6,6'-dicarboxylic acid) featuring steric hindrance and enhanced hydrophilicity on the backbone. Combining experimental evidence with systematic density functional theory calculations on the Ru-bnda and related catalysts Ru-bda, Ru-pda and Ru-biqa, we emphasized that seven coordination clearly determines presence of RuV=O with high spin density on the ORuV=O atom, i.e. oxo with radical properties, which is one of the necessary conditions for reacting through the O-O coupling pathway. However, an additional factor to make the condition sufficient is the favorable intermolecular face-to-face interaction for the generation of the pre-reactive [RuV=O...O=RuV], which is significantly influenced by the secondary coordination environments. This work provides a new understanding of the structure-activity relationship of water-oxidation catalysts and their potential to adopt I2M pathway for O-O bond formation.
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