- Introducing Water-Network-Assisted Proton Transfer for Boosted Electrocatalytic Hydrogen Evolution with Cobalt Corrole
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Proton transfer is vital for many biological and chemical reactions. Hydrogen-bonded water-containing networks are often found in enzymes to assist proton transfer, but similar strategy has been rarely presented by synthetic catalysts. We herein report the Co corrole 1 with an appended crown ether unit and its boosted activity for the hydrogen evolution reaction (HER). Crystallographic and 1H NMR studies proved that the crown ether of 1 can grab water via hydrogen bonds. By using protic acids as proton sources, the HER activity of 1 was largely boosted with added water, while the activity of crown-ether-free analogues showed very small enhancement. Inhibition studies by adding 1) external 18-crown-6-ether to extract water molecules and 2) potassium ion or N-benzyl-n-butylamine to block the crown ether of 1 further confirmed its critical role in assisting proton transfer via grabbed water molecules. This work presents a synthetic example to boost HER through water-containing networks.
- Li, Xialiang,Lv, Bin,Zhang, Xue-Peng,Jin, Xiaotong,Guo, Kai,Zhou, Dexia,Bian, Hongtao,Zhang, Wei,Apfel, Ulf-Peter,Cao, Rui
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supporting information
(2022/01/11)
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- Ammonia-Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNNHComplexes
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Metal complexes incorporating proton-responsive ligands have been proved to be superior catalysts in reactions involving the H2 molecule. In this contribution, a series of IrIII complexes based on lutidine-derived CNNH pincers containing N-heterocyclic carbene and secondary amino NHR [R = Ph (4a), tBu (4b), benzyl (4c)] donors as flanking groups have been synthesized and tested in the dehydrogenation of ammonia-borane (NH3BH3, AB) in the presence of substoichiometric amounts (2.5 equiv) of tBuOK. These preactivated derivatives are efficient catalysts in AB dehydrogenation in THF at room temperature, albeit significantly different reaction rates were observed. Thus, by using 0.4 mol% of 4a, 1.0 equiv of H2 per mole of AB was released in 8.5 min (turnover frequency (TOF50%) = 1875 h-1), while complexes 4b and 4c (0.8 mol%) exhibited lower catalytic activities (TOF50% = 55-60 h-1). 4a is currently the best performing IrIII homogeneous catalyst for AB dehydrogenation. Kinetic rate measurements show a zero-order dependence with respect to AB, and first order with the catalyst in the dehydrogenation with 4a (-d[AB]/dt = k[4a]). Conversely, the reaction with 4b is second order in AB and first order in the catalyst (-d[AB]/dt = k[4b][AB]2). Moreover, the reactions of the derivatives 4a and 4b with an excess of tBuOK (2.5 equiv) have been analyzed through NMR spectroscopy. For the former precursor, formation of the iridate 5 was observed as a result of a double deprotonation at the amine and the NHC pincer arm. In marked contrast, in the case of 4b, a monodeprotonated (at the pincer NHC-arm) species 6 is observed upon reaction with tBuOK. Complex 6 is capable of activating H2 reversibly to yield the trihydride derivative 7. Finally, DFT calculations of the first AB dehydrogenation step catalyzed by 5 has been performed at the DFT//MN15 level of theory in order to get information on the predominant metal-ligand cooperation mode.
- álvarez, Eleuterio,López-Serrano, Joaquín,Ortega-Lepe, Isabel,Rendón, Nuria,Rossin, Andrea,Sánchez, Práxedes,Santos, Laura L.,Suárez, Andrés
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p. 18490 - 18502
(2021/12/01)
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- Bis-Imidazole Methane Ligated Ruthenium(II) Complexes: Synthesis, Characterization, and Catalytic Activity for Hydrogen Production from Formic Acid in Water
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A series of half sandwich arene-ruthenium complexes [(η6-arene)RuCl(κ2-L)]+ ([Ru]-1-[Ru]-10) containing bis-imidazole methane-based ligands {4,4′-(phenylmethylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L1), {4,4′-((4-methoxyphenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L2), {4,4′-((2-methoxyphenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L3), {4,4′-((4-chlorophenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L4), and {4,4′-((2-chlorophenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L5) are synthesized. The synthesized and purified complexes ([Ru]-1-[Ru]-10) are further employed for hydrogen production from formic acid in aqueous medium. Among the investigated complexes, [(η6-p-cymene)RuCl(κ2-L2)]+ [Ru]-2, having Ru(II) coordinated 4-methoxy phenyl substituted bis-imidazole methane ligand (L2), outperformed over others, displaying a higher catalytic turnover of 8830 and high efficiency (TOF = 1545 h-1) with appreciably high long-term stability for formic acid dehydrogenation in water.
- Deka, Hemanta,Patra, Soumyadip,Singh, Sanjay K.
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supporting information
p. 14275 - 14285
(2021/10/05)
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- Pd/C-Catalyzed H2 Evolution from Tetrahydroxydiboron Hydrolysis
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The production of H2 from non-fossil sources is a key research challenge to contributing solving the forthcoming energy problem. Aqueous solutions of tetrahydroxydiboron have very recently appeared as a H2 source, from which both hydrogen atoms are provided by water, in the presence of highly sophisticated nanocatalysts. Herein, commercial and cheap Pd/C is shown to be an efficient and recyclable catalyst for H2 evolution upon tetrahydroxydiboron hydrolysis. Graphic Abstract: [Figure not available: see fulltext.]
- Zhou, Junjie,Huang, Yu,Shen, Jialu,Liu, Xiang
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p. 3004 - 3010
(2021/02/12)
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- Activation of Molecular Hydrogen by Inter- and Intramolecular Al?N Lewis Pairs
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The field of frustrated Lewis pair chemistry offers many opportunities to activate molecular hydrogen, but Al?N systems have not been established yet. In this work, we describe several intermolecular classical Al?N Lewis pairs and an intramolecular ortho-
- Bodach, Alexander,N?thling, Nils,Felderhoff, Michael
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supporting information
p. 1240 - 1243
(2021/02/26)
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- Hydrolysis of B2pin2 over Pd/C Catalyst: High Efficiency, Mechanism, and in situ Tandem Reaction
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A facile and effective synthesis of H2 or D2 from Pd/C catalyzed hydrolysis of B2pin2 has first been developed. Among them, B2pin2 is frequently used for borylation reaction, and has rarely been used for hydrogen evolution. The kinetic isotope effects (KIEs) and tandem reaction for diphenylacetylene and norbornene hydrogenation have confirmed both two H atoms of H2 gas are provided from H2O. This is contrary to other boron compounds hydrolysis (including NH3BH3, NaBH4), which generates H2 with only one H atom provided by water and the other one by boron compounds. Note that the hydrolysis of B2pin2 in D2O also provides an easy and useful synthesis of D2.
- Li, Ning,Shen, Jialu,Liu, Xiang
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supporting information
p. 2797 - 2800
(2021/02/16)
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- Acid- and Base-Catalyzed Hydrolytic Hydrogen Evolution from Diboronic Acid
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The efficient production of H2 from hydrogen-rich sources, particularly from water, is a crucial task and a great challenge, both as a sustainable energy source and on the laboratory scale for hydrogenation reactions. Herein, a facile and effective synthesis of H2 and D2 from only acid- or base-catalyzed metal-free hydrolysis of B2(OH)4, a current borylation reagent, has been developed without any transition metal or ligand. Acid-catalyzed H2 evolution was completed in 4 min, whereas the base-catalyzed process needed 6 min. The large kinetic isotopic effects for this reaction with D2O, deuteration experiments and mechanistic studies have confirmed that both H atoms of H2 originate from water using either of these reactions. This new, metal-free catalytic system holds several advantages, such as high efficiency, simplicity of operation, sustainability, economy, and potential further use.
- Wang, Yi,Shen, Jialu,Huang, Yu,Liu, Xiang,Zhao, Qiuxia,Astruc, Didier
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p. 3013 - 3018
(2021/03/26)
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- Bifunctional activation of amine-boranes by the W/Pd bimetallic analogs of “frustrated Lewis pairs”
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The reaction between basic [(PCP)Pd(H)] (PCP = 2,6-(CH2P(t-C4H9)2)2C6H4) and acidic [LWH(CO)3] (L = Cp (1a), Tp (1b); Cp = η5-cyclopentadienyl, Tp = κ3-hydridotris(pyrazolyl)borate) leads to the formation of bimolecular complexes [LW(CO)2(μ-CO)?Pd(PCP)] (4a,4b), which catalyze amine-borane (Me2NHBH3tBuNH2BH3) dehydrogenation. The combination of variable-temperature (1H,31P{1H},11B NMR and IR) spectroscopies and computational (ωB97XD/def2-TZVP) studies reveal the formation of an η1-borane complex [(PCP)Pd(Me2NHBH3)]+[LW(CO3)]?(5) in the first step, where a BH bond strongly binds palladium and an amine group is hydrogen-bonded to tungsten. The subsequent intracomplex proton transfer is the rate-determining step, followed by an almost barrierless hydride transfer. Bimetallic species4are easily regenerated through hydrogen evolution in the reaction between two hydrides.
- Osipova, Elena S.,Gulyaeva, Ekaterina S.,Gutsul, Evgenii I.,Kirkina, Vladislava A.,Pavlov, Alexander A.,Nelyubina, Yulia V.,Rossin, Andrea,Peruzzini, Maurizio,Epstein, Lina M.,Belkova, Natalia V.,Filippov, Oleg A.,Shubina, Elena S.
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p. 3682 - 3692
(2021/03/26)
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- Ligand Design for Catalytic Dehydrogenation of Formic Acid to Produce High-pressure Hydrogen Gas under Base-free Conditions
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A series of Cp*Ir (Cp? = pentamethylcyclopentadienyl anion) complexes with amino-functionalized ligands were developed for the production of high-pressure H2 via catalytic dehydrogenation of formic acid (DFA) in water under base-free conditions. The Ir complexes with 2,2′-bipyridine (bpy) ligands bearing amino or alkylamino groups at the para positions exhibited high activity and stability for DFA compared with complexes containing bpy ligands bearing para-hydroxyl groups. In addition, para-amino groups afforded superior catalytic stability under high-pressure conditions compared with ortho-amino groups. By exploiting these amino-functionalized Cp*Ir complexes, it was possible to continuously produce high-pressure CO-free H2 via selective DFA in water upon the addition of concentrated FA (>99.5 wt %) to the base-free solution. Systematic investigation of the ligand effects on DFA revealed that the presence of alkylamino groups on the bpy ligand enhanced the catalytic activity (initial turnover frequency, TOF), although the stability decreased with increasing alkyl chain length on the amino groups. According to a Hammett plot, the increased catalytic activity of the Ir complexes after the introduction of amino-functionalized ligands may be attributable to the electron-donating effect of para-amino groups on the bpy ligand. Based on the experimental results, a reaction mechanism is proposed that involves a hydride intermediate whose stability is affected by the position of the amino groups on the bpy ligand, as confirmed through NMR studies.
- Kawanami, Hajime,Iguchi, Masayuki,Himeda, Yuichiro
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p. 4191 - 4199
(2020/03/10)
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- Cooperative effects of heterodinuclear IrIII?MII complexes on catalytic H2 evolution from formic acid dehydrogenation in water
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Novel heterodinuclear IrIII?MII complexes (M = Co, Ni, or Cu) with two adjacent reaction sites were synthesized by using 3,5-bis(2-pyridyl)-pyrazole (Hbpp) as a structure-directing ligand and employed as catalysts for H2 evolution through formic acid dehydrogenation in water. A cooperative effect of the hetero-metal centers was observed in the H2 evolution in comparison with the corresponding mononuclear IrIII and MII complexes as the components of the IrIII?MII complexes. The H2 evolution rate for the IrIII?MII complexes was at most 350-fold higher than that of the mononuclear IrIII complex. The catalytic activity increased in the following order: IrIII?CuII complex III?CoII complex III?NiII complex . The IrIII?H intermediates of the IrIII?MII complexes were successfully detected by ultraviolet?visible, 1H , nuclear magnetic resonance, and ESI-TOF-MS spectra. The catalytic enhancement of H2 evolution by the IrIII?MII complexes indicates that the IrIII?H species formed in the IrIII moiety act as reactive species and the MII moieties act as acceleration sites by the electronic effect from the MII center to the IrIII center through the bridging bpp? ligand. The IrIII?MII complexes may also activate H2O at the 3d MII centers as a proton source to facilitate H2 evolution. In addition, the affinity of formate for the IrIII?MII complexes was investigated on the basis of Michaelis?Menten plots; the IrIII?CoII and IrIII?NiII complexes exhibited affinities that were relatively higher than that of the IrIII?CuII complex. The catalytic mechanism of H2 evolution by the IrIII?MII complexes was revealed on the basis of spectroscopic detection of reaction intermediates, kinetic analysis, and isotope labeling experiments.
- Hong, Dachao,Shimoyama, Yoshihiro,Ohgomori, Yuji,Kanega, Ryoichi,Kotani, Hiroaki,Ishizuka, Tomoya,Kon, Yoshihiro,Himeda, Yuichiro,Kojima, Takahiko
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p. 11976 - 11985
(2020/11/23)
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- Photocatalytic proton reduction by a computationally identified, molecular hydrogen-bonded framework
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We show that a hydrogen-bonded framework, TBAP-α, with extended π-stacked pyrene columns has a sacrificial photocatalytic hydrogen production rate of up to 3108 μmol g-1 h-1. This is the highest activity reported for a molecular organic crystal. By comparison, a chemically-identical but amorphous sample of TBAP was 20-200 times less active, depending on the reaction conditions, showing unambiguously that crystal packing in molecular crystals can dictate photocatalytic activity. Crystal structure prediction (CSP) was used to predict the solid-state structure of TBAP and other functionalised, conformationally-flexible pyrene derivatives. Specifically, we show that energy-structure-function (ESF) maps can be used to identify molecules such as TBAP that are likely to form extended π-stacked columns in the solid state. This opens up a methodology for the a priori computational design of molecular organic photocatalysts and other energy-relevant materials, such as organic electronics.
- Aitchison, Catherine M.,Chen, Linjiang,Clowes, Rob,Cooper, Andrew I.,Day, Graeme M.,Kane, Christopher M.,Little, Marc A.,Mcmahon, David P.,Pulido, Angeles,Spackman, Peter R.,Sprick, Reiner Sebastian,Wang, Xiaoyan,Wilbraham, Liam,Zwijnenburg, Martijn A.
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supporting information
p. 7158 - 7170
(2020/04/22)
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- Photocatalyst Z-scheme system composed of a linear conjugated polymer and BiVO4for overall water splitting under visible light
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Linear conjugated polymers have potential as photocatalysts for hydrogen production from water but so far, most studies have involved non-scalable sacrificial reagents. Z-schemes comprising more than one semiconductor are a potential solution, but it is challenging to design these systems because multiple components must work together synergistically. Here, we show that a conjugated polymer photocatalyst for proton reduction can be coupled in a Z-scheme with an inorganic water oxidation photocatalyst to promote overall water splitting without any sacrificial reagents. First, a promising combination of an organic catalyst, an inorganic catalyst, and a redox mediator was identified by using high-throughput screening of a library of components. A Z-scheme system composed of P10 (homopolymer of dibenzo[b,d]thiophene sulfone)-Fe2+/Fe3+-BiVO4 was then constructed for overall water splitting under visible light irradiation. Transient absorption spectroscopy was used to assign timescales to the various steps in the photocatalytic process. While the overall solar-to-hydrogen efficiency of this first example is low, it provides proof of concept for other hybrid organic-inorganic Z-scheme architectures in the future. This journal is
- Aitchison, Catherine M.,Bai, Yang,Cooper, Andrew I.,Cowan, Alexander J.,Kudo, Akihiko,Nakagawa, Keita,Sprick, Reiner Sebastian,Yamaguchi, Yuichi,Zwijnenburg, Martijn A.
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supporting information
p. 16283 - 16290
(2020/11/03)
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- The large subunit of the regulatory [NiFe]-hydrogenase fromRalstonia eutropha- a minimal hydrogenase?
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Chemically synthesized compounds that are capable of facilitating the reversible splitting of dihydrogen into protons and electrons are rare in chemists' portfolio. The corresponding biocatalysts - hydrogenases - are, however, abundant in the microbial world. [NiFe]-hydrogenases represent a major subclass and display a bipartite architecture, composed of a large subunit, hosting the catalytic NiFe(CO)(CN)2cofactor, and a small subunit whose iron-sulfur clusters are responsible for electron transfer. To analyze in detail the catalytic competence of the large subunit without its smaller counterpart, we purified the large subunit HoxC of the regulatory [NiFe]-hydrogenase of the model H2oxidizerRalstonia eutrophato homogeneity. Metal determination and infrared spectroscopy revealed a stoichiometric loading of the metal cofactor. This enabled for the first time the determination of the UV-visible extinction coefficient of the NiFe(CO)(CN)2cofactor. Moreover, the absence of disturbing iron-sulfur clusters allowed an unbiased look into the low-spin Fe2+of the active site by M?ssbauer spectroscopy. Isolated HoxC was active in catalytic hydrogen-deuterium exchange, demonstrating its capacity to activate H2. Its catalytic activity was drastically lower than that of the bipartite holoenzyme. This was consistent with infrared and electron paramagnetic resonance spectroscopic observations, suggesting that the bridging position between the active site nickel and iron ions is predominantly occupied by water-derived ligands, even under reducing conditions. In fact, the presence of water-derived ligands bound to low-spin Ni2+was reflected by the absorption bands occurring in the corresponding UV-vis spectra, as revealed by time-dependent density functional theory calculations conducted on appropriatein silicomodels. Thus, the isolated large subunits indeed represent simple [NiFe]-hydrogenase models, which could serve as blueprints for chemically synthesized mimics. Furthermore, our data point to a fundamental role of the small subunit in preventing water access to the catalytic center, which significantly increases the H2splitting capacity of the enzyme.
- Breglia, Raffaella,Caserta, Giorgio,Ciaccafava, Alexandre,Cramer, Stephen P.,Greco, Claudio,Hildebrandt, Peter,Keck, Matthias,Lenz, Oliver,Limberg, Christian,Lorent, Christian,Zebger, Ingo
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p. 5453 - 5465
(2020/06/10)
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- Design considerations for chiral frustrated Lewis pairs: B/N FLPs derived from 3,5-bicyclic aryl piperidines
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Herein, 3,5-bicyclic aryl piperidines are derivatized to generate chiral B/N FLPs. Initially, the twofold symmetric amine C6H2F2(C5H8NiPr) 1 was converted in a series of synthetic steps to the styrene-derivative C6HF2(C5H8NiPr)(CH═CH2) 4. Efforts to hydroborate the vinyl fragment proved challenging as a result of the strongly basic nitrogen, although the species C6HF2(C5H8N(H)iPr)(CH2CH2B(OH)(C6F5)2) 5 was crystallographically characterized. Modification of the system was achieved by conversion of the amine C6H2F2(C5H8NH) 6 to C6HF2(C5H8NPh)(CH═CH2) 9. Hydroboration of 9 with 9-BBN or HB(C6F5)2 gave C6HF2(C5H8NPh)(CH2CH2BBN) 10 or C6HF2(C5H8NPh)(CH2CH2B(C6F5)2) 11, respectively. The latter species was derivatized by complexation of PPh3 to give C6HF2(C5H8NPh)(CH2CH2B(C6F5)2)(PPh3) 12. The Lewis acidities of 10 and 11 were assessed by the Gutman-Beckett test and by computations of the FIA and GEI. While 10 did not effect HD scrambling or hydrogenation of N-phenylbenzylimine, 11 was effective in HD scrambling. Despite this, no reduction of N-t-butylbenzylimine or N-phenylbenzylimine was achieved. These data demonstrate that 10 lacks the threshold combination of Lewis acidity and basicity to activate H2, while 11 lacks the steric demands about boron to preclude classical Lewis acid-base bond formation with imine substrates.
- Lam, Jolie,Sampaolesi, Susanna,LaFortune, James H. W.,Coe, Jotham W.,Stephan, Douglas W.
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supporting information
p. 133 - 141
(2019/01/04)
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- Assembly of Ultra-Thin NiO Layer Over Zn1?xCdxS for Stable Visible-Light Photocatalytic Overall Water Splitting
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Photocatalytic splitting of water into hydrogen and oxygen by using visible light is considered to be a clean, green, and renewable route for solar energy conversion and storage. Although the Zn1?xCdxS catalysts show comparatively higher activity for photocatalytic hydrogen generation under visible-light irradiation, they suffer from serious photocorrosion during the photocatalytic reaction. The deposition of a protective layer over the Zn1?xCdxS catalysts is believed to be an effective way to inhibit photocorrosion. However, only a few materials exhibit satisfactory catalytic properties for hydrogen evolution as well as a good protection ability. In this work, a new Zn1?xCdxS photocatalyst was developed for water splitting under visible-light illumination by assembling an ultrathin NiO layer over Zn0.8Cd0.2S through an in situ photodeposition method. The as-prepared NiO/Zn0.8Cd0.2S showed significantly higher activity for overall water splitting compared with Pt/Zn0.8Cd0.2S under the same conditions without photocorrosion. An apparent quantum efficiency of 0.66 % was achieved for hydrogen evolution at 430 nm with an accomplished multicycle stability for up to 12 h without any significant decay. The strong electronic coupling between the NiO layer and Zn1?xCdxS also promoted efficient charge separation and migration.
- Ning, Xiaofeng,Zhen, Wenlong,Zhang, Xuqiang,Lu, Gongxuan
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p. 1410 - 1420
(2019/03/21)
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- Visible light-catalytic dehydrogenation of benzylic alcohols to carbonyl compounds by using an eosin y and nickel-thiolate complex dual catalyst system
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We developed a simple and environmentally benign visible-light-driven dehydrogenation of benzylic alcohols to the corresponding aldehydes or ketones. By using the dual catalyst system consisting of eosin Y as a photocatalyst and a Ni(ii) complex as a proton reduction catalyst, we could dehydrogenate benzylic alcohols to aldehydes or ketones with excellent yields under mild conditions. The sole byproduct is hydrogen gas.
- Yang, Xiu-Jie,Zheng, Li-Qiang,Wu, Li-Zhu,Tung, Chen-Ho,Chen, Bin
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supporting information
p. 1401 - 1405
(2019/03/26)
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- Tailoring the Porosity in Iron Phosphosulfide Nanosheets to Improve the Performance of Photocatalytic Hydrogen Evolution
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Metal sulfide photocatalysts are typically required during water splitting to produce hydrogen. However, the rapid recombination of photogenerated electron–hole pairs in these highly unstable photocatalysts has restricted hydrogen production to small-scale batch reactions. In this work, porous transition-metal thiophosphites were used to enable continuous long-term hydrogen production through photocatalysis. A wide bandgap (2.04 eV) was essential for generating hydrogen at a rate of 305.6 μmol h?1 g?1, 180 % faster than nonporous FePS3 nanosheets. More importantly, the high in-plane stiffness of these approximately 7 nm thick porous FePS3 nanosheets ensured structural stability during 56 h of continuous photocatalysis reactions. The reaction results with D2O instead of H2O indicated that hydrogen mainly came from H2O. Furthermore, a sacrificial reagent (triethylamine) was photodegraded into diethylamine and acetaldehyde through a monoelectronic oxidation process, as indicated by HPLC and LC–MS. This synthesis strategy reported for FePS3 porous nanosheets paves a new pathway for designing other dianion-based inorganic nanocrystals for hydrogen energy applications.
- Zhang, Jian,Feng, Fang,Pu, Yong,Li, Xing'ao,Lau, Cher Hon,Huang, Wei
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p. 2651 - 2659
(2019/06/27)
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- The Nature of Hydrogen Adsorption on Platinum in the Aqueous Phase
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The thermodynamic state of H2 adsorbed on Pt in the aqueous phase was determined by kinetic analysis of H2 reacting with D2O to HDO, HD, and D2, and by DFT-based ab initio molecular dynamics simulations of H2 adsorption on Pt(111), Pt(110), and Pt nanoparticles. Dissociative adsorption of H2 on Pt is significantly weakened in the aqueous phase compared to adsorption at gas–solid interfaces. Water destabilizes the adsorbed H atoms, decreasing the heat of adsorption by 19–22 kJ (Formula presented.) while inducing an additional entropy loss of 50–70 J (Formula presented.) K?1. Upon dissociative adsorption of H2, the average distance of water from the Pt surface increases and the liquid adopts a structure that is more ordered than before close to the Pt surface, which limits the translation mobility of the adsorbed H atoms. The presence of hydrated hydronium ions next to the Pt surface further lowers the H?Pt bond strength.
- Yang, Guoju,Akhade, Sneha A.,Chen, Xi,Liu, Yue,Lee, Mal-Soon,Glezakou, Vassiliki-Alexandra,Rousseau, Roger,Lercher, Johannes A.
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supporting information
p. 3527 - 3532
(2019/02/05)
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- Combinatorial Identification of Hydrides in a Ligated Ag40 Nanocluster with Noncompact Metal Core
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No formation of bulk silver hydride has been reported. Until very recently, only a few silver nanoclusters containing hydrides have been successfully prepared. However, due to the lack of effective techniques and also poor stability of hydride-containing Ag nanoclusters, the identification of hydrides' location within Ag nanoclusters is challenging and not yet achieved, although some successes have been reported on clusters of several Ag atoms. In this work, we report a detailed structural and spectroscopic characterization of the [Ag40(DMBT)24(PPh3)8H12]2+ (Ag40H12) cluster (DMBT = 2,4-dimethylbenzenethiol). The metal framework consists of three concentric shells of Ag8?Ag24?Ag8, which can be described as (ν1-cube)?(truncated-ν3-octahedron)?(ν2-cube), respectively. The presence of 12 hydrides in each cluster was systematically identified by various techniques. Based on a detailed analysis of the structural features and 1H and 2H NMR spectra, the positions of the 12 hydrides were determined to be residing on the 12 edges of the cubic core. As a result, the electron count of the Ag40 cluster is a two-electron superatomic system instead of a 14-electron system. Moreover, based on our DFT calculations and experimental probes, it was demonstrated that the 12 hydrides play a crucial role in stabilizing both the electronic and geometric structure of the Ag40H12 cluster. The successful synthesis of stable hydride-containing Ag nanoclusters and the identification of hydride positions are expected to simulate research attention on both synthesis and application of hydride-containing Ag nanomaterials.
- Yuan, Xiting,Sun, Cunfa,Li, Xihua,Malola, Sami,Teo, Boon K.,H?kkinen, Hannu,Zheng, Lan-Sun,Zheng, Nanfeng
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supporting information
p. 11905 - 11911
(2019/08/26)
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- The Role of Proton Shuttles in the Reversible Activation of Hydrogen via Metal-Ligand Cooperation
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The reversible activation of H2 via a pathway involving metal-ligand cooperation (MLC) is proposed to be important in many transition metal catalyzed hydrogenation and dehydrogenation reactions. Nevertheless, there is a paucity of experimental information probing the mechanism of this transformation. Here, we present an in-depth kinetic study of the 1,2-addition of H2 via an MLC pathway to the widely used iron catalyst [(iPrPNP)FeH(CO)] (1) (iPrPNP = N(CH2CH2PiPr2)2 -). We report one of the first experimental demonstrations of an enhancement in rate for the activation of H2 using protic additives, which operate as "proton shuttles". Our results indicate that proton shuttles need to be able to both simultaneously donate and accept a proton, and the best shuttles are molecules that are strong hydrogen bond donors but sufficiently weak acids to avoid deleterious protonation of the transition metal complex. Additionally, comparison of the rate of H2 activation via an MLC pathway between 1 and two widely used ruthenium catalysts enables more general conclusions about the role of the metal, ancillary ligand, and proton shuttles in H2 activation. The results of this study provide guidance about the design of catalysts and additives to promote H2 activation via an MLC pathway.
- Smith, Nicholas E.,Bernskoetter, Wesley H.,Hazari, Nilay
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supporting information
p. 17350 - 17360
(2019/10/28)
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- Diacetylene Functionalized Covalent Organic Framework (COF) for Photocatalytic Hydrogen Generation
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Covalent organic frameworks (COFs) are crystalline, highly porous, two- or three-dimensional polymers with tunable topology and functionalities. Because of their higher chemical stabilities in comparison to their boron-linked counterparts, imine or β-ketoenamine linked COFs have been utilized for a broad range of applications, including gas storage, heterogeneous catalysis, energy storage devices, or proton-conductive membranes. Herein, we report the synthesis of highly porous and chemically stable acetylene (-C≡C-) and diacetylene (-C≡C-C≡C-) functionalized β-ketoenamine COFs, which have been applied as photocatalyst for hydrogen generation from water. It is shown that the diacetylene moieties have a profound effect as the diacetylene-based COF largely outperforms the acetylene-based COF in terms of photocatalytic activity. As a combined effect of high porosity, easily accessible diacetylene (-C≡C-C≡C-) functionalities and considerable chemical stability, an efficient and recyclable heterogeneous photocatalytic hydrogen generation is achieved.
- Pachfule, Pradip,Acharjya, Amitava,Roeser, Jér?me,Langenhahn, Thomas,Schwarze, Michael,Schom?cker, Reinhard,Thomas, Arne,Schmidt, Johannes
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supporting information
p. 1423 - 1427
(2018/02/09)
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- Photocatalytic oxidation of arylalcohols to aromatic aldehydes promoted by hydroxyl radicals over a CoP/CdS photocatalyst in water with hydrogen evolution
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Cobalt phosphide (CoP) combined with CdS was employed as a photocatalyst to oxidize arylalcohols into aromatic aldehydes or ketones in water. This was accompanied by the reduction of water, and the quantitative yield of hydrogen evolution was much higher than the chemical equivalent of hydrogen gas. Electron spin resonance spectroscopy and quenching experiments demonstrated that hydroxyl free radicals, originating from water splitting, promoted the oxidation of arylalcohols, while the holes in the valence band of the photocatalyst were reduced by the -OH and organic substrates. The overall reaction generates high-value-added organics. This photocatalytic reaction is atom-economical, in accordance with the concept of sustainable development.
- Xu, Yong,Zeng, Ling-Zhen,Fu, Zi-Cheng,Li, Cong,Yang, Zhi,Chen, Yong,Fu, Wen-Fu
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p. 2540 - 2545
(2018/05/30)
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- Another Unprecedented Wieland Mechanism Confirmed: Hydrogen Formation from Hydrogen Peroxide, Formaldehyde, and Sodium Hydroxide
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In 1923, Wieland and Wingler reported that in the molecular hydrogen producing reaction of hydrogen peroxide with formaldehyde in basic solution, free hydrogen atoms (H.) are not involved. They postulated that bis(hydroxymethyl)peroxide, HOCH2OOCH2OH, is the intermediate, which decomposes to yield H2 and formate, proposing a mechanism that would nowadays be considered as a “concerted process”. Since then, several other (conflicting) “mechanisms” have been suggested. Our NMR and Raman spectroscopic and kinetic studies, particularly the determination of the deuterium kinetic isotope effect (DKIE), now confirm that in this base-dependent reaction, both H atoms of H2 derive from the CH2 hydrogen atoms of formaldehyde, and not from the OH groups of HOCH2OOCH2OH or from water. Quantum-chemical CBS-QB3 and W1BD computations show that H2 release proceeds through a concerted process, which is strongly accelerated by double deprotonation of HOCH2OOCH2OH, thereby ruling out a free radical pathway.
- Czochara, Robert,Litwinienko, Grzegorz,Korth, Hans-Gert,Ingold, Keith U.
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supporting information
p. 9146 - 9149
(2018/05/05)
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- Alkali Metal Species in the Reversible Activation of H2
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MP(tBu)2 (M=Li, Na, K), KH and KN(SiMe3)2 are shown to activate HD reversibly. In the case of MP(tBu)2 this leads to isotopic scrambling and the formation of H2, D2, H(D)P(tBu)2 and MH(D) in C6D6. In toluene, KP(tBu)2 reacts with H2 but also leads to isotopic scrambling into the methyl groups of the solvent toluene. DFT calculations reveal that these systems effect H2 activation via cooperative interactions with the Lewis acidic alkali metal and the basic phosphorus, carbanion, or hydride centres, mimicking frustrated Lewis pair (FLP) behaviour.
- Xu, Maotong,Jupp, Andrew R.,Qu, Zheng-Wang,Stephan, Douglas W.
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supporting information
p. 11050 - 11054
(2018/07/30)
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- Exploring the Reactivity of Donor-Stabilized Phosphenium Cations: Lewis Acid-Catalyzed Reduction of Chlorophosphanes by Silanes
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Phosphane-stabilized phosphenium cations react with silanes to effect either reduction to primary or secondary phosphanes, or formation of P-P bonded species depending upon counteranion. This operates for in situ generated phosphenium cations, allowing catalytic reduction of P(III)-Cl bonds in the absence of strong reducing agents. Anion and substituent dependence studies have allowed insight into the competing mechanisms involved.
- Pearce, Kyle G.,Borys, Andryj M.,Clark, Ewan R.,Shepherd, Helena J.
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supporting information
p. 11530 - 11536
(2018/09/21)
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- Decomposition of formic acid over silica encapsulated and amine functionalised gold nanoparticles
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Formic acid has recently attracted considerable attention as a safe and convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage. Here, we show that silica encapsulated and amine functionalised gold nanoparticles are h
- Mielby, Jerrik,Kunov-Kruse, Andreas Jonas,Kegn?s, S?ren
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p. 149 - 156
(2016/12/16)
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- A homogeneous molecular system for the photogeneration of hydrogen from water based on a [RuII(bpy)3]2+ photosensitizer and a phthalycyanine cobalt catalyst
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In this contribution, we report an efficient homogeneous system for the visible light-driven H2 production from aqueous protons. This comprises a macrocyclic phthalycyanine cobalt complex [CoIIPc(-2)] as a hydrogen-evolving catalyst (HEC), [RuII(bpy)3]Cl2 (bpy?=?2,2′-bipyridine) as a photosensitizer (PS) and triethylamine (TEA) as a sacrificial electron donor (SED). The system gives up to 2400 TON versus the catalyst with an initial TOF as high as 680 TON h?1. Phthalocyanine cobalt and its derivatives are a promising new direction for molecular catalysts readily accessible in a large scale and low-cost achieving the photogeneration of H2.
- Xie, An,Liu, Xiao-Lei,Xiang, Yu-Chen,Luo, Geng-Geng
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supporting information
p. 226 - 231
(2017/05/16)
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- Efficient Water Reduction with sp3-sp3 Diboron(4) Compounds: Application to Hydrogenations, H–D Exchange Reactions, and Carbonyl Reductions
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A series of crystalline sp3-sp3 diboron(4) compounds were synthesized and shown to promote the facile reduction of water with dihydrogen formation. The application of these diborons as simple and effective dihydrogen and dideuterium sources was demonstrated by conducting a series of selective reductions of alkynes and alkenes, and hydrogen–deuterium exchange reactions using two-chamber reactors. Finally, as the water reduction reaction generates an intermediate borohydride species, a range of aldehydes and ketones were reduced by using water as the hydride source.
- Flinker, Mathias,Yin, Hongfei,Juhl, René W.,Eikeland, Espen Z.,Overgaard, Jacob,Nielsen, Dennis U.,Skrydstrup, Troels
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supporting information
p. 15910 - 15915
(2017/11/23)
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- Light-Driven Hydrogen Generation from Microemulsions Using Metallosurfactant Catalysts and Oxalic Acid
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A unique microemulsion-based photocatalytic water reduction system is demonstrated. Iridium- and rhodium-based metallosurfactants, namely, [Ir(ppy)2(dhpdbpy)]Cl and [Rh(dhpdbpy)2Cl2]Cl (where ppy = 2-phenylpyridine and dhpdbpy = 4,4′-diheptadecyl-2,2′-bipyridine), were employed as photosensitizer and proton reducing catalyst, respectively, along with oxalic acid as a sacrificial reductant in a toluene/water biphasic mixture. The addition of 1-octylamine is proposed to initiate the reaction, by coupling with oxalic acid to form an ion pair, which acts as an additional surfactant. Concentration optimizations yielded high activity for both the photosensitizer (240 turnovers, turnover frequency (TOF) = 200 h-1) and catalyst (400 turnovers, TOF = 230 h-1), with the system generating hydrogen even after 95 h. Mechanistic insights were provided by gas-phase Raman, electrochemical, and luminescence quenching analysis, suggesting oxidative quenching to be the principle reaction pathway.
- Kagalwala, Husain N.,Chirdon, Danielle N.,Mills, Isaac N.,Budwal, Nikita,Bernhard, Stefan
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supporting information
p. 10162 - 10171
(2017/09/12)
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- Unravelling the Mechanism of Basic Aqueous Methanol Dehydrogenation Catalyzed by Ru-PNP Pincer Complexes
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Ruthenium PNP complex 1a (RuH(CO)Cl(HN(C2H4Pi-Pr2)2)) represents a state-of-the-art catalyst for low-temperature (2 and CO2. Herein, we describ
- Alberico, Elisabetta,Lennox, Alastair J. J.,Vogt, Lydia K.,Jiao, Haijun,Baumann, Wolfgang,Drexler, Hans-Joachim,Nielsen, Martin,Spannenberg, Anke,Checinski, Marek P.,Junge, Henrik,Beller, Matthias
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supporting information
p. 14890 - 14904
(2016/11/29)
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- Hemilabile Bridging Thiolates as Proton Shuttles in Bioinspired H2 Production Electrocatalysts
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Synthetic analogues and computationally assisted structure-function analyses have been used to explore the features that control proton-electron and proton-hydride coupling in electrocatalysts inspired by the [NiFe]-hydrogenase active site. Of the bimetallic complexes derived from aggregation of the dithiolato complexes MN2S2 (N2S2 = bismercaptoethane diazacycloheptane; M = Ni or Fe(NO)) with (η5-C5H5)Fe(CO)+ (the Fe′ component) or (η5-C5H5)Fe(CO)2+, Fe″, which yielded Ni-Fe′+, Fe-Fe′+, Ni-Fe″+, and Fe-Fe″+, respectively, both Ni-Fe′+ and Fe-Fe′+ were determined to be active electrocatalysts for H2 production in the presence of trifluoroacetic acid. Correlations of electrochemical potentials and H2 generation are consistent with calculated parameters in a predicted mechanism that delineates the order of addition of electrons and protons, the role of the redox-active, noninnocent NO ligand in electron uptake, the necessity for Fe′-S bond breaking (or the hemilability of the metallodithiolate ligand), and hydride-proton coupling routes. Although the redox active {Fe(NO)}7 moiety can accept and store an electron and subsequently a proton (forming the relatively unstable Fe-bound HNO), it cannot form a hydride as the NO shields the Fe from protonation. Successful coupling occurs from a hydride on Fe′ with a proton on thiolate S and requires a propitious orientation of the H-S bond that places H+ and H- within coupling distance. This orientation and coupling barrier are redox-level dependent. While the Ni-Fe′ derivative has vacant sites on both metals for hydride formation, the uptake of the required electron is more energy intensive than that in Fe-Fe′ featuring the noninnocent NO ligand. The Fe′-S bond cleavage facilitated by the hemilability of thiolate to produce a terminal thiolate as a proton shuttle is a key feature in both mechanisms. The analogous Fe″-S bond cleavage on Ni-Fe″ leads to degradation.
- Ding, Shengda,Ghosh, Pokhraj,Lunsford, Allen M.,Wang, Ning,Bhuvanesh, Nattamai,Hall, Michael B.,Darensbourg, Marcetta Y.
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supporting information
p. 12920 - 12927
(2016/10/13)
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- Inorganic clusters with a [Fe2MoOS3] core - A functional model for acetylene reduction by nitrogenases
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We report the first example of a wholly inorganic mimic of a part of the FeMoco active centre of nitrogenases. We detail the synthesis, characterisation and reactivity of two related, transient hydride-containing inorganic clusters, a dihydride complex and a vinyl monohydride complex, which bear the [Fe2MoOS3] portion of FeMoco. The dihydride complex is capable of reducing acetylene to ethylene via the vinyl monohydride complex. In the reaction cycle, a transient low-valent complex was generated by the reductive elimination of H2 or ethylene from dihydride or vinyl monohydride complexes, respectively.
- Yoshimoto, Koji,Yatabe, Takeshi,Matsumoto, Takahiro,Tran, Viet-Ha,Robertson, Andrew,Nakai, Hidetaka,Asazawa, Koichiro,Tanaka, Hirohisa,Ogo, Seiji
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p. 14620 - 14627
(2016/09/28)
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- Co(dmgH)2pyCl as a noble-metal-free co-catalyst for highly efficient photocatalytic hydrogen evolution over hexagonal ZnIn2S4
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Co(dmgH)2pyCl/ZnIn2S4 composites (dmgH = dimethylglyoxime and py = pyridine) with different amounts of Co(dmgH)2pyCl loaded were prepared from hexagonal ZnIn2S4 and Co(dmgH)2pyCl
- Gao, Yanhong,Lin, Huaxiang,Zhang, Shiying,Li, Zhaohui
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p. 6072 - 6076
(2016/02/03)
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- In situ preparation of a MOF-derived magnetic carbonaceous catalyst for visible-light-driven hydrogen evolution
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MOFs (Metal-Organic Frameworks) have emerged as novel photocatalysts for water reduction but are frequently plagued by their instability when exposed to moist and strongly acidic or alkaline reaction environments. Herein we employed a volatile Fe-based MOF in alkaline solution as precursor to evolve into a magnetic carbonaceous photocatalyst in situ, which demonstrated highly efficient visible-light-driven hydrogen evolution (~125 μmol H2 produced within 6 h using 5 mg of MOF precursor) with a quantum efficiency of 1.8% even in the absence of noble metal cocatalyst, indicative of a possible photocatalytic system containing only earth-abundant elements for long-term conversion of solar light into hydrogen energy. The catalyst exhibited an apparent stoichiometric formula of FeO3.3C0.2H1.0 and was determined to be essentially a carbon-metal oxides/oxyhydroxides composite. Laser photolysis and electrochemical measurements were performed to visualize the fundamental multistep electron transfer processes during water reduction, which opens a strategy for the rational design of MOF-derived catalysts to dramatically increase H2 evolution efficiency.
- Xu, Jing-Yin,Zhai, Xin-Ping,Gao, Lin-Feng,Chen, Peng,Zhao, Min,Yang, Hong-Bin,Cao, Deng-Feng,Wang, Qiang,Zhang, Hao-Li
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p. 2011 - 2018
(2016/01/20)
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- Mechanism of a one-photon two-electron process in photocatalytic hydrogen evolution from ascorbic acid with a cobalt chlorin complex
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A one-photon two-electron process was made possible in photocatalytic H2 evolution from ascorbic acid with a cobalt(ii) chlorin complex [CoII(Ch)] via electron transfer from ascorbate to the excited state of [Ru(bpy)3]2+ followed by electron transfer from [Ru(bpy)3]+ to CoII(Ch) with proton to give the hydride complex, which reacts with proton to produce H2. [CoIII(Ch)]+ was reduced by ascorbate to reproduce CoII(Ch).
- Aoi, Shoko,Mase, Kentaro,Ohkubo, Kei,Fukuzumi, Shunichi
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supporting information
p. 15145 - 15148
(2015/10/12)
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- Cobalt phosphide as a highly active non-precious metal cocatalyst for photocatalytic hydrogen production under visible light irradiation
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Cobalt phosphide (Co2P) is found, for the first time, to be a novel cocatalyst for efficient photocatalytic hydrogen evolution for a system containing CdS nanorods as a photocatalyst and dl-mandelic acid as an electron donor in water. Under optimal conditions, the H2-production rate can reach up to 19 373 μmolh-1 g-1 after 10 h of LED light irradiation. Meanwhile, dl-mandelic acid can be oxidized to benzoylformic acid by the photo-generated holes of CdS nanorods, providing a green and economic way to synthesize benzoylformic acid from dl-mandelic acid.
- Cao, Shuang,Chen, Yong,Hou, Chun-Chao,Lv, Xiao-Jun,Fu, Wen-Fu
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supporting information
p. 6096 - 6101
(2015/03/14)
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- Facile structure design based on C3N4 for mediator-free Z-scheme water splitting under visible light
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In this work, two photocatalysts (i.e., C3N4 and WO3) were successfully combined into a heterojunction structure by a facile hydrothermal method for mediator-free overall water splitting, analogous to the natural photosynthesis over a two-step photoexcitation Z-scheme system. Hydrogen and oxygen are evolved with a 2:1 ratio by irradiating the C3N4-WO3 composites loaded with Pt under visible light (λ > 420 nm) without any redox mediator. Introducing reduced graphene oxide (rGO) into the C3N4-WO3 composites enhances the water splitting efficiency. Through optimizing the mass ratio in the C3N4-WO3 composites, rGO content, amount of loaded Pt and pH value of the reacting system, the highest H2/O2 evolution rates of 2.84 and 1.46 μmol h-1 can be obtained, with a quantum yield of 0.9%. Our findings demonstrate that the hydrothermal method is a promising strategy for constructing intimate heterostructures for Z-scheme water-splitting systems without using any redox mediator, and that rGO can be used to further enhance the performance in optimized conditions.
- Zhao, Guixia,Huang, Xiubing,Fina, Federica,Zhang, Guan,Irvine, John T. S.
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p. 3416 - 3422
(2015/06/08)
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- Photocatalytic water reduction from a noble-metal-free molecular dyad based on a thienyl-expanded BODIPY photosensitizer
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A noble-metal-free molecular dyad was constructed by anchoring a thienyl-expanded BODIPY photosensitizer (PS) to a cobaloxime catalyst, which gives a 2.5-fold increase in the TON, and a 3-fold enhancement in the quantum efficiency as compared to the multicomponent catalytic system for the generation of hydrogen via the reduction of water. The stability of PS was expected to improve by introducing the thienyl moiety into the BODIPY core.
- Luo, Geng-Geng,Fang, Kai,Wu, Ji-Huai,Mo, Jun
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supporting information
p. 12361 - 12364
(2015/08/03)
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- The decomposition of methanol on Au-Pt bimetallic clusters supported by a thin film of Al2O3/NiAl(100)
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With various techniques to probe a surface, we studied the decomposition of methanol on Au-Pt bimetallic clusters, of diameter ≤6.0 nm, formed by sequential deposition of Au and Pt evaporated onto thin-film Al 2O3/NiAl(100). The surface of the bimetallic clusters comprised both Au and Pt, but the decomposition, through dehydrogenation to CO and scission of the C-O bond, proceeded primarily on the surface Pt. Alloying of Pt with Au altered little the dehydrogenation on the Pt sites. The CO and hydrogen produced from dehydrogenated methanol increased with the extent of Pt sites; the production per surface Pt was comparable to that of Pt clusters. The temperature of the onset of dehydrogenation resembled that of Pt clusters. Little methanol decomposed to CO on the Au sites. Varying the surface structure and composition of the bimetallic clusters affected these properties insignificantly. In contrast to the dehydrogenation, scission of the C-O bond in methanol did not depend exclusively on the concentration of Pt atoms at the surface, given that production of methane from this second channel did not increase with the extent of Pt surface sites. The modified electronic structure of the alloyed Pt controlled the probability of the C-O bond scission. The bimetallic clusters restructured during the reaction such that the Au atoms in the clusters aggregated and decorated the Pt surface, leading to fewer surface Pt and increased mean coordination of surface Au.
- Li,Liao,Wang,Chao,Hung,Ho,Luo,Lai, Yu-Ling,Hsu, Yao-Jane
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p. 31602 - 31613
(2014/08/18)
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- Molecular hydrogen formation from proximal glycol pairs on TiO 2(110)
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Understanding hydrogen formation on TiO2 surfaces is of great importance, as it could provide fundamental insight into water splitting for hydrogen production using solar energy. In this work, hydrogen formation from glycols having different numbers of methyl end-groups has been studied using temperature-programmed desorption on reduced, hydroxylated, and oxidized rutile TiO2(110) surfaces. The results from OD-labeled glycols demonstrate that gas-phase molecular hydrogen originates exclusively from glycol hydroxyl groups. The yield is controlled by a combination of glycol coverage, steric hindrance, TiO2(110) order, and the amount of subsurface charge. Combined, these results show that proximal pairs of hydroxyl-aligned glycol molecules and subsurface charge are required to maximize the yield of this redox reaction. These findings highlight the importance of geometric and electronic effects in hydrogen formation from adsorbates on TiO2(110).
- Chen, Long,Li, Zhenjun,Smith, R. Scott,Kay, Bruce D.,Dohnálek, Zdenek
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supporting information
p. 5559 - 5562
(2014/05/06)
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- Formic acid dehydrogenation with bioinspired iridium complexes: A kinetic isotope effect study and mechanistic insight
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Highly efficient hydrogen generation from dehydrogenation of formic acid is achieved by using bioinspired iridium complexes that have hydroxyl groups at the ortho positions of the bipyridine or bipyrimidine ligand (i.e., OH in the second coordination sphere of the metal center). In particular, [Ir(Cp*)(TH4BPM)(H2O)]SO4 (TH4BPM: 2,2′,6,6′-tetrahydroxyl-4,4′-bipyrimidine; Cp*: pentamethylcyclopentadienyl) has a high turnover frequency of 39 500 h-1 at 80 °C in a 1 M aqueous solution of HCO2H/HCO2Na and produces hydrogen and carbon dioxide without carbon monoxide contamination. The deuterium kinetic isotope effect study clearly indicates a different rate-determining step for complexes with hydroxyl groups at different positions of the ligands. The rate-limiting step is β-hydrogen elimination from the iridium-formate intermediate for complexes with hydroxyl groups at ortho positions, owing to a proton relay (i.e., pendent-base effect), which lowers the energy barrier of hydrogen generation. In contrast, the reaction of iridium hydride with a proton to liberate hydrogen is demonstrated to be the rate-determining step for complexes that do not have hydroxyl groups at the ortho positions. The key controls the mechanism: A deuterium kinetic isotope effect (KIE) study clearly indicates a different mechanism for complexes with OH at different positions of the ligands. The rate-limiting step is β-hydrogen elimination from the iridium-formate intermediate for complexes with OH at ortho positions owing to a proton relay (i.e., pendent-base effect), which lowers the energy barrier of generation of H2.
- Wang, Wan-Hui,Xu, Shaoan,Manaka, Yuichi,Suna, Yuki,Kambayashi, Hide,Muckerman, James T.,Fujita, Etsuko,Himeda, Yuichiro
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p. 1976 - 1983
(2014/08/18)
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- Base-free production of H2 by dehydrogenation of formic acid using an iridium-bisMETAMORPhos complex
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Erase the base: An iridium complex based on a cooperative ligand that functions as an internal base is reported. This complex can rapidly and cleanly dehydrogenate formic acid in absence of external base, a reaction that is required if formic acid is to be exploited as an energy carrier (see scheme). Copyright
- Oldenhof, Sander,De Bruin, Bas,Lutz, Martin,Siegler, Maxime A.,Patureau, Frederic W.,Van Der Vlugt, Jarl Ivar,Reek, Joost N. H.
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supporting information
p. 11507 - 11511
(2013/09/12)
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- Molecular hydrogen formation from photocatalysis of methanol on TiO 2(110)
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It is well established that adding methanol to water could significantly enhance H2 production by TiO2. Recently, we have found that methanol can be photocatalytically dissociated on TiO2(110) at 400 nm via a stepwise mechanism. However, how molecular hydrogen can be formed from the photocatalyzed methanol/TiO2(110) surface is still not clear. In this work, we have investigated deuterium formation from photocatalysis of the fully deuterated methanol (CD3OD) on TiO 2(110) at 400 nm using a temperature programmed desorption (TPD) technique. Photocatalytic dissociation products formaldehyde (CD2O) and D-atoms on BBO sites (via D2O TPD product) have been detected. In addition to D2O formation by heating the photocatalyzed methanol/TiO2(110) surface, we have also observed D2 product formation. D2 is clearly formed via thermal recombination of the D-atoms on the BBO sites from photocatalysis of methanol. Experimental results indicate that D2O formation is more important than D 2 formation and that D2 formation is clearly affected by the D2O formation process.
- Xu, Chenbiao,Yang, Wenshao,Guo, Qing,Dai, Dongxu,Chen, Maodu,Yang, Xueming
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p. 10206 - 10209
(2013/08/23)
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- Artificial Z-scheme constructed with a supramolecular metal complex and semiconductor for the photocatalytic reduction of CO2
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A hybrid for the visible-light-driven photocatalytic reduction of CO 2 using methanol as a reducing agent was developed by combining two different types of photocatalysts: a Ru(II) dinuclear complex (RuBLRu′) used for CO2 reduction is adsorbed onto Ag-loaded TaON (Ag/TaON) for methanol oxidation. Isotope experiments clearly showed that this hybrid photocatalyst mainly produced HCOOH (TN = 41 for 9 h irradiation) from CO 2 and HCHO from methanol. Therefore, it converted light energy into chemical energy (ΔG = +83.0 kJ/mol). Photocatalytic reaction proceeds by the stepwise excitation of Ag/TaON and the Ru dinuclear complex on Ag/TaON, similar to the photosynthesis Z-scheme.
- Sekizawa, Keita,Maeda, Kazuhiko,Domen, Kazunari,Koike, Kazuhide,Ishitani, Osamu
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supporting information
p. 4596 - 4599
(2013/05/23)
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- Iridium porphyrins in CD3OD: Reduction of Ir(III), CD 3-OD bond cleavage, Ir-D acid dissociation and alkene reactions
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Methanol solutions of iridium(III) tetra(p-sulfonatophenyl)porphyrin [(TSPP)IrIII] form an equilibrium distribution of methanol and methoxide complexes ([(TSPP)IrIII(CD3OD) (2-n)(OCD3)n]su
- Bhagan, Salome,Imler, Gregory H.,Wayland, Bradford B.
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p. 4611 - 4617
(2013/05/22)
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- Isolation of a mixed valence diiron hydride: Evidence for a spectator hydride in hydrogen evolution catalysis
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The mixed-valence diiron hydrido complex (μ-H)Fe2(pdt)(CO) 2(dppv)2 ([H1]0, where pdt =1,3- propanedithiolate and dppv = cis-1,2-C2H2(PPh 2)2), was generated by reduction of the differous hydride [H1]+ using decamethylcobaltocene. Crystallographic analysis shows that [H1]0 retains the stereochemistry of its precursor, where one dppv ligand spans two basal sites and the other spans apical and basal positions. The Fe - -Fe bond elongates to 2.80 from 2.66 A?, but the Fe-P bonds only change subtly. Although the Fe-H distances are indistinguishable in the precursor, they differ by 0.2 A? in [H1]0. The X-band electron paramagnetic resonance (EPR) spectrum reveals the presence of two stereoisomers, the one characterized crystallographically and a contribution of about 10% from a second symmetrical (sym) isomer wherein both dppv ligands occupy apical-basal sites. The unsymmetrical (unsym) arrangement of the dppv ligands is reflected in the values of A(31P), which range from 31 MHz for the basal phosphines to 284 MHz for the apical phosphine. Density functional theory calculations were employed to rationalize the electronic structure of [H1]0 and to facilitate spectral simulation and assignment of EPR parameters including 1H and 31P hyperfine couplings. The EPR spectra of [H1]0 and [D1]0 demonstrate that the singly occupied molecular orbital is primarily localized on the Fe center with the longer bond to H, that is, FeII- H···FeI. The coupling to the hydride is A( 1H) = 55 and 74 MHz for unsym- amd sym-[H1]0, respectively. Treatment of [H1]0 with H+ gives 0.5 equiv of H2 and [H1]+. Reduction of D+ affords D 2, leaving the hydride ligand intact. These experiments demonstrate that the bridging hydride ligand in this complex is a spectator in the hydrogen evolution reaction.
- Wang, Wenguang,Nilges, Mark J.,Rauchfuss, Thomas B.,Stein, Matthias
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p. 3633 - 3639
(2013/04/23)
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- Investigation and enhancement of the stability and performance of water reduction systems based on cyclometalated iridium(III) complexes
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Water reduction systems that use a bis-cyclometalated IrIII photosensitiser (PS) along with homogeneous Pd complexes as a source of in-situ-formed colloidal Pd as the water reducing complex (WRC) and triethylamine (TEA) as the sacrificial electron donor were tested and characterised with respect to their photocatalytic H2 production performance. It was confirmed that substitution of the 2-(pyridin-2-yl)benzen-1- ide (pyb) ligand in the well-known system [Ir(pyb)2(bpy)]+ (bpy=2,2′-bipyridine) by the fluorinated cyclometalating ligand 5-fluoro-2-(5-methylpyridin-2-yl)benzen-1-ide (Fmpyb) tremendously enhanced the H2 production rate. Moreover, variation of the bidentate N^N ligand bpy by alkyl substitution in the 4,4′-position resulted in an increase in the H2 production yield by a factor of three. The incident-photon-to-hydrogen-efficiency could be enhanced from 2.6 to 12.3 %. Furthermore, a new dinuclear Co complex was used as a reduction catalyst and showed up to 760 turnovers after 20 h. A detailed study of the concentration impact of all components in the photoredox system was performed. DFT calculations were used to aid the explanation of the findings. Teamwork 2.0: A highly active system for photocatalytic water reduction consisting of an Ir photosensitiser and a Pd dichloro complex as the source of catalytically active Pd0 is described. Additionally, the introduction of a hitherto unknown dinuclear Co complex as a water reduction centre resulted in a system with a comparably high initial activity. Copyright
- Hansen, Sven,Pohl, Marga-Martina,Klahn, Marcus,Spannenberg, Anke,Beweries, Torsten
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- Visible-light-driven hydrogen evolution from water using a noble-metal-free polyoxometalate catalyst
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In an effort to address the need to develop hydrolytically more stable, molecular water reduction catalysts (WRCs) amenable to in-depth investigation, we report here one prototype: a tetra-manganese-containing V-centered polyoxotungstate, Na10[Mn4(H2O) 2(VW9O34)2] (1). The electronic structure of 1 was elucidated using the DFT approach. Complex 1 is readily prepared by a one-pot procedure in aqueous solution and catalyzes the reduction of water using visible light irradiation (λ = 455 nm) with [Ru(bpy) 3]2+ and triethanolamine (TEOA) as a photosensitizer and sacrificial electron donor, respectively. Upon irradiation, the excited state [Ru(bpy)3]2+* is oxidatively quenched by 1, as confirmed by steady-state and time-resolved fluorescence decay studies, to form [Ru(bpy)3]3+ and a reduced form of the catalyst. The [Ru(bpy)3]2+ is rapidly regenerated by reaction with TEOA. The reduced form of the catalyst, 1, reacts with water to generate hydrogen. Isotope labeling experiments demonstrate that the hydrogen comes from water. The stability of the catalyst was assessed using different spectroscopic methods. A mechanism based on experimental results is proposed.
- Lv, Hongjin,Song, Jie,Zhu, Haiming,Geletii, Yurii V.,Bacsa, John,Zhao, Chongchao,Lian, Tianquan,Musaev, Djamaladdin G.,Hill, Craig L.
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- Isolation and crystal structure of the proposed low-valent active species in the H2 activation catalytic cycle
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We provide confirmation of our proposed design principles for a H 2 activation catalytic cycle by constructing a new catalyst. We have been able to obtain a crystal structure to confirm our proposition that a reduced, dinuclear species stores electrons from hydrogen molecules in a metal-metal bond.
- Inoki, Daisuke,Matsumoto, Takahiro,Nakai, Hidetaka,Ogo, Seiji
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p. 3978 - 3986
(2013/11/06)
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- Efficient subnanometric gold-catalyzed hydrogen generation via formic acid decomposition under ambient conditions
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Formic acid (FA) has tremendous potential as a safe and convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage, but controlled and efficient dehydrogenation of FA by a robust solid catalyst under ambient conditions constitutes a major challenge. Here, we report that a previously unappreciated combination of subnanometric gold and an acid-tolerant oxide support facilitates the liberation of CO-free H2 from FA. Applying an ultradispersed gold catalyst comprising TEM-invisible gold subnanoclusters deposited on zirconia to a FA-amine mixture affords turnover frequencies (TOFs) up to 1590 per hour and a turnover number of more than 118-400 at 50 °C. The reaction was accelerated at higher temperatures, but even at room temperature, a significant H2 evolution (TOFs up to 252 h-1 after 20 min) can still be obtained. Preliminary mechanistic studies suggest that the reaction is unimolecular in nature and proceeds via a unique amine-assisted formate decomposition mechanism on Au-ZrO2 interface.
- Bi, Qing-Yuan,Du, Xian-Long,Liu, Yong-Mei,Cao, Yong,He, He-Yong,Fan, Kang-Nian
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p. 8926 - 8933
(2012/07/02)
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