| 1. |
- Xue, Kai, et al.
(författare)
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Spaceborne miniaturized UHF dual band helix antenna with a small frequency ratio
- 2021
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Ingår i: Microwave and Optical Technology Letters. - : Wiley. - 1098-2760 .- 0895-2477. ; 63:6, s. 1767-1773
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Tidskriftsartikel (refereegranskat)abstract
- This study proposes a novel miniaturized circularly polarized (CP) ultrahigh frequency (UHF) quadrifilar helix antenna for spaceborne applications. The dual-band operation is realized using four inverted-U shaped helical strips (IUSHSs) that are rotated and alternately arranged on the four faces of a hollow polyimide cuboid in a sequential rotation manner, which effectively reduces the size of the antenna. Furthermore, the four IUSHSs are connected by a cross-shape strip at the top of the antenna to control the dual resonant frequencies, resulting in a small dual-band frequency ratio. The proposed antenna is both lightweight and robust when compared with the conventional miniaturized CP antennas operating at similar bands with similar performance. In particular, its compact radiator provides effective miniaturized spaceborne solution without the need of high-dielectric coefficient materials. A device for spaceborne application that operates at 402/505 MHz is designed, fabricated, measured, and in-orbit tested with a weight of 651 g and an effective size of 0.161 × 0.161 × 0.228 λ3402MHz (λ402MHz is the wavelength at 402 MHz). The measured gain and axial ratio of the proposed antenna are better than 5.32 dBi and 2.18 dB, respectively, within 2 and 12 MHz bandwidth for the two bands. The test results proved that the methods used to design the proposed antenna are effective.
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| 2. |
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| 3. |
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| 4. |
- Marcos, Rocio, et al.
(författare)
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Bicarbonate Hydrogenation Catalyzed by Iron : How the Choice of Solvent Can Reverse the Reaction
- 2016
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435 .- 2155-5435. ; 6:5, s. 2923-2929
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Tidskriftsartikel (refereegranskat)abstract
- Here we report a mechanism study of the hydrogenation of bicarbonate by tetradentate phosphines iron-complexes. It is an extension of our recent study on the reverse reaction by the same type of complexes [Chem.-Eur. J. 2013, 19, 11869], with special emphasis herein on the effects of the choice of solvent. By using density functional theory we have located the most plausible mechanism and have found remarkable effects of the solvent on the reversibility of this reaction. We predict that the solvent used in experiment, MeOH, for the hydrogenation of bicarbonate to formate could be replaced to enhance the activity of the system. There is a direct correlation of the solubility of the base to favor or disfavor the hydrogenation of bicarbonate to formate.
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| 5. |
- Sanchez-de-Armas, Rocio, et al.
(författare)
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One Site Is Enough : A Theoretical Investigation of Iron-Catalyzed Dehydrogenation of Formic Acid
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:36, s. 11869-11873
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Tidskriftsartikel (refereegranskat)abstract
- Dehydrogenation of HCO2H: The reaction mechanism for the dehydrogenation of formic acid catalyzed by a highly active and selective iron complex (see figure) has been studied by DFT. The most favorable pathway shows the hydride in Fe-H complexes acting as a spectator ligand throughout the catalytic cycle. This result opens up the Fe complex for modification in order to achieve more efficient and selective catalysts.
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| 6. |
- Toro, Liqin Xue, et al.
(författare)
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Two routes to hydrogen evolution for a Co-polypyridyl complex with two open sites
- 2022
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Ingår i: Electronic Structure. - : Institute of Physics (IOP). - 2516-1075. ; 4:3
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Tidskriftsartikel (refereegranskat)abstract
- Cobalt polypyridyl complexes efficiently catalyze hydrogen evolution in aqueous media and exhibit high stability under reducing conditions. Their stability and activity can be tuned through electronic and steric considerations, but the rationalization of these effects requires detailed mechanistic understanding. As an example, tetradentate ligands with two non-permanently occupied coordination sites show higher activity with these sites in cis compared to trans configuration. Here reaction mechanisms of the Co-polypyridyl complex [Co-II(bpma)Cl-2] (bpma = bipyridinylmethyl-pyridinylmethyl-methyl-amine) have been studied using hybrid density-functional theory. This complex has two exchangeable cis sites, and provides a flexible ligand environment with both pyridyl and amine coordination. Two main pathways with low barriers are found. One pathway, which includes both open sites, is hydrogen evolution from a Co-II-H intermediate with a water ligand as the proton donor. In the second pathway H-H bond formation occurs between the hydride and the protonated bpma ligand, with one open site acting as a spectator. The two pathways have similar barriers at higher pH, while the latter becomes more dominant at lower pH. The calculations consider a large number of interconnected variables; protonation sites, isomers, spin multiplicities, and the identities of the open binding sites, as well as their combinations, thus exploring many simultaneous dimensions within each pathway. The results highlight the effects of having two open cis-coordination sites and how their relative binding affinities change during the reaction pathway. They also illustrate why Co-II-H intermediates are more active than Co-III-H ones, and why pyridyl protonation gives lower reaction barriers than amine protonation.
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| 7. |
- Xue, Liqin, et al.
(författare)
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A DFT Study : Why Do [Ni((P2N2R')-N-R)(2)](2+) Complexes Facilitate the Electrocatalytic Oxidation of Formate?
- 2014
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 53:7, s. 3281-3289
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Tidskriftsartikel (refereegranskat)abstract
- We present a DFT study of the reaction mechanism on electrocatalytic oxidation of formate by a family of [Ni((P2N2R')-N-R)(2)](2+) complexes ((P2N2R')-N-R = 1,5-diR'-3,7-diR derivative of 1,5-diaza-3,7-diphosphacyclooctane, where R and R' are aryl or alkyl groups). [Ni((P2N2Me)-N-Ph)(2)](2+) complex 1 was used as a model complex to mimic a family of [Ni((P2N2R')-N-R)(2)](2+) complexes. Our calculated results show that the decarboxylation step (corresponding to TS3) is the rate-determining step for the electrocatalytic oxidation of formate and that a NiII-H intermediate is involved in the reaction mechanism. The pendant amine plays an important role in the deprotonation of the nickel hydride complex generated in the decarboxylation step. In addition, our study indicates that the choice of external bases is important for removing the proton (H+) from the nitrogen-protonated nickel(0) complexes. For the electrocatalytic oxidation of formate using the catalytically inactive [Ni(depe)(2)](2+) (depe = 1,2-bis(diethylphosphino)ethane) complex, calculations on 1-depe have also been carried out for comparison.
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| 8. |
- Yang, Yong, et al.
(författare)
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Nickel Complex with Internal Bases as Efficient Molecular Catalyst for Photochemical H-2 Production
- 2014
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 7:10, s. 2889-2897
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Tidskriftsartikel (refereegranskat)abstract
- A Ni complex with internal bases that contain bipyridine-derived ligands, [Ni(L)(2)(H2O)(2)](BF4)(2) ([1](BF4)(2), L=2-(2-pyridyl)-1,8-naphthyridine), and a reference complex that bears analogous bipyridine-derived ligands but without an internal base, [Ni(L)(3)](BF4)(2) ([2](BF4)(2), L=2-(2-pyridyl)quinoline), were synthesized and characterized. The electrochemical properties of these complexes were studied in CH3CN, H2O, and a mixture of EtOH/H2O. The fluorescence spectroscopic studies suggest that both dynamic and the sphere-of-action static quenching exist in the fluorescein Fl(2-)/[1](2+) and Fl(2-)/[2](2+) systems. These noble-metal-free molecular systems were studied for photocatalytic H-2 generation. Under optimal conditions, the turnover number of H-2 evolution reaches 3230 based on [1](2+), whereas [2](2+) displays only approximately one third of the turnover of [1](2+). A plausible mechanism for the catalytic H-2 generation by [1](2+) is presented based on DFT calculations.
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