| 1. |
- Abdel-Magied, Ahmed F., et al.
(författare)
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Substituent Effects in Molecular Ruthenium Water Oxidation Catalysts Based on Amide Ligands
- 2017
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Ingår i: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 9:9, s. 1583-1587
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Tidskriftsartikel (refereegranskat)abstract
- The production of clean and sustainable energy is considered as one of the most urgent issues for our society. Mastering the oxidation of water to dioxygen is essential for the production of solar fuels. A study of the influence of the substituents on the catalytic activity of a series of mononuclear Ru complexes (2a-e) based on a tetradentate ligand framework is presented. At neutral pH, using [Ru(bpy)(3)](PF6)(3) (bpy=2,2'-bipyridine) as the terminal oxidant, a good correlation between the turnover frequency (TOF) and the Hammett sigma(meta) parameters was obtained. Additionally, a general pathway for the deactivation of Ru-based catalysts 2a-e during the catalytic oxidation of water through poisoning by carbon monoxide was demonstrated. These results highlight the importance of ligand design for fine-tuning the catalytic activity of water oxidation catalysts.
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| 2. |
- An, Wei, et al.
(författare)
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Mechanistic Study of CO Titration on CuxO/Cu(111) (x <= 2) Surfaces
- 2014
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Ingår i: ChemCatChem. - : Wiley-VCH Verlagsgesellschaft. - 1867-3880 .- 1867-3899. ; 6:8, s. 2364-2372
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Tidskriftsartikel (refereegranskat)abstract
- The reducibility of metal oxides is of great importance to their catalytic behavior. Herein, we combined ambient-pressure scanning tunneling microscopy (AP-STM), X-ray photoemission spectroscopy (AP-XPS), and DFT calculations to study the CO titration of CuxO thin films supported on Cu(111) (CuxO/Cu(111)) aiming to gain a better understanding of the roles that the Cu(111) support and surface defects play in tuning catalytic performances. Different conformations have been observed during the reduction, namely, the 44 structure and a recently identified (5-7-7-5) Stone-Wales defects (5-7 structure). The DFT calculations revealed that the Cu(111) support is important to the reducibility of supported CuxO thin films. Compared with the case for the Cu2O(111) bulk surface, at the initial stage CO titration is less favorable on both the 44 and 5-7 structures. The strong CuxO <-> Cu interaction accompanied with the charge transfer from Cu to CuxO is able to stabilize the oxide film and hinder the removal of O. However, with the formation of more oxygen vacancies, the binding between CuxO and Cu(111) is weakened and the oxide film is destabilized, and Cu2O(111) is likely to become the most stable system under the reaction conditions. In addition, the surface defects also play an essential role. With the proceeding of the CO titration reaction, the 5-7 structure displays the highest activity among all three systems. Stone-Wales defects on the surface of the 5-7 structure exhibit a large difference from the 44 structure and Cu2O(111) in CO binding energy, stability of lattice oxygen, and, therefore, the reduction activity. The DFT results agree well with the experimental measurements, demonstrating that by adopting the unique conformation, the 5-7 structure is the active phase of CuxO, which is able to facilitate the redox reaction and the Cu2O/Cu(111)<-> Cu transition.
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| 3. |
- Arnold, Polly L., et al.
(författare)
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Controlled Photocatalytic Hydrocarbon Oxidation by Uranyl Complexes
- 2019
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Ingår i: ChemCatChem. - : Wiley-VCH Verlagsgesellschaft. - 1867-3880 .- 1867-3899. ; 11:16, s. 3786-3790
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Tidskriftsartikel (refereegranskat)abstract
- Controlled, photocatalytic C-H bond activations are key reactions in the toolkits of the modern synthetic chemist. While it is known that the uranyl(VI) ion, [(UO2)-O-VI](2+), the environmentally dominant form of uranium, is photoactive, most literature examines its luminescent properties, neglecting its potential synthetic utility for photocatalytic C-H bond cleavage. Here, we synthesise and fully characterise an air-stable and hydrocarbon-soluble uranyl phenanthroline complex, [(UO2)-O-VI(NO3)(2)(Ph(2)phen)], U-Ph2phen, and demonstrate that it can catalytically abstract hydrogen atoms from a variety of organic substrates under visible light irradiation. We show that the commercially available parent complex, uranyl nitrate ([(UO2)-O-VI(NO3)(2)(OH2)(2)]center dot 4H(2)O; U-NO3), is also competent, but from electronic spectroscopy we attribute the higher rates and selectivity of U-Ph2phen to ligand-mediated electronic effects. Ketones are selectively formed over other oxygenated products (alcohols, etc.), and the catalytic oxidation of substrates containing a benzylic C-H position is particularly improved for U-Ph2phen. We also show uranyl-mediated photocatalytic C-C bond cleavage in a model lignin compound for the first time.
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| 4. |
- Asahina, Shunsuke, et al.
(författare)
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Exploitation of Surface-Sensitive Electrons in Scanning Electron Microscopy Reveals the Formation Mechanism of New Cubic and Truncated Octahedral CeO(2) Nanoparticles
- 2011
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Ingår i: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 3:6, s. 1038-1044
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Tidskriftsartikel (refereegranskat)abstract
- Development of new analytical tools for nanostructures directly contributes to the study of catalysts. By using scanning electron microscopy (SEM) with a newly designed signal enhancer, we study cubic and truncated octahedral cerium oxide (CeO(2)) nanoparticles, which are composed of smaller primary octahedral CeO(2) and are formed through bond formation with hexanedioic acid. The signal enhancer is designed to efficiently collect secondary electrons of kinetic energy less than 10 eV; thus, it greatly improves the S/N ratio. On the basis of the observed SEM images and electron backscattered diffraction patterns of the cross section of the nanoparticles, we discuss the formation mechanism of the nanoparticles and speculate that the primary CeO(2) nanocrystals share their edges in the cubic nanoparticles and truncated octahedral nanoparticles. These results will contribute to the preparation of nanostructured metal oxide surfaces with controlled morphologies that could enhance catalytic activity.
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| 5. |
- Awan, Iqra Zubair, et al.
(författare)
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Design of Multicationic Copper-Bearing Layered Double Hydroxides for Catalytic Application in Biorefinery
- 2023
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Ingår i: ChemCatChem. - : Wiley. - 1867-3899 .- 1867-3880. ; 15:6
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Tidskriftsartikel (refereegranskat)abstract
- Ethanol has been used as a renewable hydrogen-donor in the conversion of a lignin model molecule in subcritical conditions. Noble metal-free porous mixed oxides, obtained by activation of Cu−Ni−Al and Cu−Ni−Fe layered double hydroxide (LDH) precursors, have been used as heterogeneous catalysts for Meerwein-Ponndorf-Verley (MPV) hydrogen transfer and further hydrogenation by ethanol dehydrogenation products. Both the Cu/(Cu+Ni) ratio and the nature of the trivalent cation (Al or Fe) affect the activity of the catalysts, as well as the selectivity towards the different steps of the hydrogenation reactions and the cleavage of lignin-like phenylether bonds. Accounting for the peculiar behaviour of Cu2+ and M(III) cations in the synthesis of LDHs, the coprecipitation of the precursors has been monitored by titration experiments. Structural and textural properties of the catalysts are closely related to the composition of the LDH precursors.
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| 6. |
- Buitrago, Elina, et al.
(författare)
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High Throughput Screening of a Catalyst Library for the Asymmetric Transfer Hydrogenation of Heteroaromatic Ketones : Formal Syntheses of (R)-Fluoxetine and (S)-Duloxetine
- 2012
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Ingår i: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 4:12, s. 2082-2089
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Tidskriftsartikel (refereegranskat)abstract
- A total of 21 amino acid based ligands including hydroxy amide, thioamide, and hydroxamic acid functionalities, respectively, were combined with [Ru(p-cymene)Cl2]2 and [RhCp*Cl2]2, and used as catalysts for the asymmetric transfer hydrogenation of four different heteroaromatic ketones in 2-propanol. The reactions were performed on a Chemspeed automated high-throughput screening robotic platform. Optimal catalysts were identified for the individual heterocyclic substrate classes. Based on these results, the formal syntheses of the antidepressant drugs (R)-fluoxetine and (S)-duloxetine were conducted by using the found catalysts in the key reaction step, which results in high isolated yields (94?%) and excellent product enantioselectivities (>99?% ee) of the formed 1,3-amino alcohols.
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| 7. |
- Busch, Michael, et al.
(författare)
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Exploring the Mechanism of Cr(VI) Catalyzed Hypochlorous Acid Decomposition
- 2022
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Ingår i: Chemcatchem. - : Wiley. - 1867-3880 .- 1867-3899. ; 14:15
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Tidskriftsartikel (refereegranskat)abstract
- Chlorate is produced through electrolysis of a chloride containing electrolyte in an undivided cell. Cr(VI) is added to the electrolyte in order to minimize the amount of oxygen formed through the homogeneous decomposition of hypochlorite. Despite the importance of Cr(VI) for the chlorate process we posses only very limited knowledge regarding the active Cr(VI) species and mechanisms through which it aids chlorate formation and inhibits O-2 evolution. Using density functional theory (DFT) modeling we present for the first time a detailed reaction mechanism for the chromate catalyzed chlorate formation. Our calculations indicate, that the reaction is initialized by the formation of a Cr(VI)-O-ClOCl species which forms Cr(VI)-OClO intermediate. This step is found to be rate determining with a rate constant which is comparable to the disproportionation reaction without catalyst. Chlorate is then obtained either through an uncatalyzed oxidation of chlorite to chlorate or the nucleophilic attack of OCl- followed by a second Cl- elimination step. The comparison of the activity of the different Cr(VI) species reveals that only CrO42- is active whereas HCrO4- and Cr2O72- display sluggish kinetics.
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| 8. |
- Busch, Michael, 1983, et al.
(författare)
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Improving the Thermodynamic Profiles of Prospective Suzuki–Miyaura Cross-Coupling Catalysts by Altering the Electrophilic Coupling Component
- 2018
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Ingår i: ChemCatChem. - : Wiley. - 1867-3899 .- 1867-3880. ; 10:7, s. 1592-1597
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Tidskriftsartikel (refereegranskat)abstract
- As a heavily used technique for forming new C−C bonds, developing new catalysts and reaction conditions for Suzuki–Miyaura cross-couplings is highly desirable. By using molecular volcano plots, the influence of the electrophilic coupling component in catalytic cycle thermodynamics is revealed. Less reactive electrophiles, such as iodine, broaden the volcano plateau, which leads to a larger number of catalysts having appealing thermodynamic profiles. Whereas, fluorine and other more reactive electrophiles compress the volcano plateau, which shrinks the pool of catalysts having good thermodynamic profiles. As a result, judicious selection of the electrophile employed in a reaction may represent an appealing strategy for further tuning the thermodynamics of cross-coupling reactions.
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| 9. |
- Chan, Fan Liang, et al.
(författare)
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Kinetic Study of Catalytic Steam Gasification of Biomass by Using Reactive Flash Volatilisation
- 2015
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Ingår i: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 7:8, s. 1329-1337
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Tidskriftsartikel (refereegranskat)abstract
- Reactive flash volatilisation is an autothermal process to convert biomass into tar-free synthesis gas under steam-rich conditions. This article studies the kinetics of reactive flash volatilisation by using Ni, Pt[BOND]Ni, Ru[BOND]Ni, Re[BOND]Ni, and Rh[BOND]Ni catalysts supported on alumina. The rates of mass loss of cellulose, xylan, and lignin were measured and compared with those of the synthetic biomass mixture and pinewood sawdust. The kinetic parameters were calculated with and without catalysts by using a wire-mesh isothermal thermogravimetric analyser in an equimolar steam/N2 atmosphere and high heating rates of 8.6×102, 1.1×103, and 1.3×104 °C min−1 at 700, 750, and 800 °C, respectively. The results revealed three distinct regimes of the rate of mass loss: pyrolytic decomposition, reforming, and char gasification. The catalysts increased the rate of mass loss in the reforming regime. Rh[BOND]Ni and Ru[BOND]Ni supported catalysts showed higher reforming rates than other catalysts. This study provides direct evidence of the in situ catalytic removal of tar during gasification of biomass
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| 10. |
- Chen, Hu, et al.
(författare)
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A Cobalt-Based Film for Highly Efficient Electrocatalytic Water Oxidation in Neutral Aqueous Solution
- 2016
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Ingår i: ChemCatChem. - : Wiley-Blackwell. - 1867-3880 .- 1867-3899. ; 8:17, s. 2757-2760
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Tidskriftsartikel (refereegranskat)abstract
- A cobalt-based film (Co-Hi) for water oxidation was prepared in 2-[4-(2-hydroxyethyl) piperazin-1-yl]ethanesulfonic acid buffer at pH 7.0 through a unique cyclic voltammetry electrodeposition method by applying a wide scan range from 1.40 to -1.00 V versus normal hydrogen electrode (NHE). This catalyst film displayed highly efficient activity during oxygen evolution in neutral aqueous solution. An impressive current density of more than 1.5 mAcm(-2) that was stable over a prolonged time period was obtained with a remarkably low onset overpotential of 230 mV in 0.1 M phosphate buffer (pH 7.0).
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