Showing papers on "Cobalt published in 2012"
TL;DR: This comprehensive tutorial review focuses on well-defined cobalt complexes that serve as homogeneous catalysts for the production of polycarbonates and cyclic carbonates from the coupling of carbon dioxide and epoxides.
Abstract: This comprehensive tutorial review focuses on well-defined cobalt complexes that serve as homogeneous catalysts for the production of polycarbonates and cyclic carbonates from the coupling of carbon dioxide and epoxides. Special considerations are given to the mechanistic pathways involved in these processes.
945 citations
TL;DR: It is found that a robust nanoparticulate electrocatalytic material, H(2-CoCat, can be electrochemically prepared from cobalt salts in a phosphate buffer and can be converted on anodic equilibration into the previously described amorphous cobalt oxide film (O(2)-CoCat or CoPi) catalysing O(2) evolution.
Abstract: The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable and efficient systems for the conversion and storage of renewable energy sources. The production of hydrogen through water splitting seems a promising and appealing solution. We found that a robust nanoparticulate electrocatalytic material, H(2)-CoCat, can be electrochemically prepared from cobalt salts in a phosphate buffer. This material consists of metallic cobalt coated with a cobalt-oxo/hydroxo-phosphate layer in contact with the electrolyte and mediates H(2) evolution from neutral aqueous buffer at modest overpotentials. Remarkably, it can be converted on anodic equilibration into the previously described amorphous cobalt oxide film (O(2)-CoCat or CoPi) catalysing O(2) evolution. The switch between the two catalytic forms is fully reversible and corresponds to a local interconversion between two morphologies and compositions at the surface of the electrode. After deposition, the noble-metal-free coating thus functions as a robust, bifunctional and switchable catalyst.
740 citations
TL;DR: A novel Mn(3)O(4)/CoSe(2) hybrid which could be a promising candidate for OER catalysts and shows good stability in 0.1 M KOH electrolyte, which is highly required to a promising OER electrocatalyst.
Abstract: The design of efficient, cheap, and abundant oxygen evolution reaction (OER) catalysts is crucial to the development of sustainable energy sources for powering fuel cells. We describe here a novel Mn3O4/CoSe2 hybrid which could be a promising candidate for such electrocatalysts. Possibly due to the synergetic chemical coupling effects between Mn3O4 and CoSe2, the constructed hybrid displayed superior OER catalytic performance relative to its parent CoSe2/DETA nanobelts. Notably, such earth-abundant cobalt (Co)-based catalyst afforded a current density of 10 mA cm–2 at a small overpotential of ∼0.45 V and a small Tafel slope down to 49 mV/decade, comparable to the best performance of the well-investigated cobalt oxides. Moreover, this Mn3O4/CoSe2 hybrid shows good stability in 0.1 M KOH electrolyte, which is highly required to a promising OER electrocatalyst.
599 citations
TL;DR: This tutorial review describes one approach to the reduction of carbon dioxide to carbon fuels, using cobalt and nickel molecular catalysts, with particular focus on studying the thermodynamics and kinetics of CO(2) binding to metal catalytic sites.
Abstract: In our developing world, carbon dioxide has become one of the most abundant greenhouse gases in the atmosphere. It is a stable, inert, small molecule that continues to present significant challenges toward its chemical activation as a useful carbon end product. This tutorial review describes one approach to the reduction of carbon dioxide to carbonfuels, using cobalt and nickel molecular catalysts, with particular focus on studying the thermodynamics and kinetics of CO2 binding to metal catalytic sites.
565 citations
TL;DR: An open-circuit voltage of over 1,000 mV is reported in mesoscopic dye-sensitized solar cells incorporating a molecularly engineered cobalt complex as redox mediator, indicating that the molecularly engineering cobalt redox shuttle is a legitimate alternative to the commonly used I3−/I− redox Shuttle.
Abstract: Dye-sensitized solar cells are a promising alternative to traditional inorganic semiconductor-based solar cells. Here we report an open-circuit voltage of over 1,000 mV in mesoscopic dye-sensitized solar cells incorporating a molecularly engineered cobalt complex as redox mediator. Cobalt complexes have negligible absorption in the visible region of the solar spectrum, and their redox properties can be tuned in a controlled fashion by selecting suitable donor/acceptor substituents on the ligand. This approach offers an attractive alternate to the traditional I(3)(-)/I(-) redox shuttle used in dye-sensitized solar cells. A cobalt complex using tridendate ligands [Co(bpy-pz)(2)](3+/2+)(PF(6))(3/2) as redox mediator in combination with a cyclopentadithiophene-bridged donor-acceptor dye (Y123), adsorbed on TiO(2), yielded a power conversion efficiency of over 10% at 100 mW cm(-2). This result indicates that the molecularly engineered cobalt redox shuttle is a legitimate alternative to the commonly used I(3)(-)/I(-) redox shuttle.
564 citations
TL;DR: It is proposed that the cobalt treatment enhances PEC performance via two mechanisms: passivating surface states on the N-modified TiO(2) surface and acting as a water oxidation cocatalyst.
Abstract: We report hydrothermal synthesis of single crystalline TiO(2) nanowire arrays with unprecedented small feature sizes of ~5 nm and lengths up to 4.4 μm on fluorine-doped tin oxide substrates. A substantial amount of nitrogen (up to 1.08 atomic %) can be incorporated into the TiO(2) lattice via nitridation in NH(3) flow at a relatively low temperature (500 °C) because of the small cross-section of the nanowires. The low-energy threshold of the incident photon to current efficiency (IPCE) spectra of N-modified TiO(2) samples is at ~520 nm, corresponding to 2.4 eV. We also report a simple cobalt treatment for improving the photoelectrochemical (PEC) performance of our N-modified TiO(2) nanowire arrays. With the cobalt treatment, the IPCE of N-modified TiO(2) samples in the ultraviolet region is restored to equal or higher values than those of the unmodified TiO(2) samples, and it remains as high as ~18% at 450 nm. We propose that the cobalt treatment enhances PEC performance via two mechanisms: passivating surface states on the N-modified TiO(2) surface and acting as a water oxidation cocatalyst.
499 citations
TL;DR: In this paper, a carbon-supported Co3O4 electrocatalyst with nano-rods and spherical structures is reported for the oxygen reduction reaction (ORR) in alkaline media.
Abstract: We report preparation of carbon-supported Co3O4 electrocatalysts with nano-rods and spherical structures by the solvent-mediated morphological control method. The catalytic properties of the prepared catalysts for the oxygen reduction reaction (ORR) in alkaline media are investigated. We show that the ORR catalytic activity of the prepared catalysts is sensitive to the number and activity of surface-exposed Co3+ ions that can be tailored by the morphology of cobalt oxides. In particular, we demonstrate that the non-precious Co3O4 electrocatalyst with the nano-rod structure (∼12 nm in length and ∼5.1 nm in diameter) prepared in the mixed solvent of water to dimethylformamide ratio of 1 : 1 exhibits a higher current density than a much more expensive palladium-based catalyst does at the low potential region.
481 citations
TL;DR: This new route for the preparation of a nitrogen-doped graphene nanocomposite with carbon nanotube offers synthetic control of morphology and nitrogen functionality and shows promise for applications in nonaqueous oxygen reduction electrocatalysis for Li-O(2) battery cathodes.
Abstract: In this work, we present a synthesis approach for nitrogen-doped graphene-sheet-like nanostructures via the graphitization of a heteroatom polymer, in particular, polyaniline, under the catalysis of a cobalt species using multiwalled carbon nanotubes (MWNTs) as a supporting template. The graphene-rich composite catalysts (Co-N-MWNTs) exhibit substantially improved activity for oxygen reduction in nonaqueous lithium-ion electrolyte as compared to those of currently used carbon blacks and Pt/carbon catalysts, evidenced by both rotating disk electrode and Li–O2 battery experiments. The synthesis–structure–activity correlations for the graphene nanostructures were explored by tuning their synthetic chemistry (support, nitrogen precursor, heating temperature, and transition metal type and content) to investigate how the resulting morphology and nitrogen-doping functionalities (e.g., pyridinic, pyrrolic, and quaternary) influence the catalyst activity. In particular, an optimal temperature for heat treatment du...
462 citations
TL;DR: In this paper, the authors reviewed the recent important progress in electrocatalytic hydrogen production catalyzed by earth-abundant metal complexes and classified them into two categories depending on the media used in the hydrogen-evolving reactions with an emphasis on the types of acids employed.
Abstract: This perspective article reviews the recent important progress in electrocatalytic hydrogen production catalyzed by earth-abundant metal complexes. The catalysts are divided into two categories depending on the media used in the hydrogen-evolving reactions, with an emphasis on the types of acids employed. The catalysts used in the first category, which work in organic solutions, include nickel and cobalt complexes with base-containing diphosphine ligands, cobaloximes, cobalt tetrapyridine complexs, and [NiFe]- and [FeFe]-hydrogenase mimics. Molybdenum and cobalt pentapyridine complexes, as well as the cobalt bis(iminopyridine) complex reported very recently, are the most important examples of catalysts used in the second category, which work in aqueous solutions. The advantages and disadvantages of the different types of catalysts are discussed and the hydrogen-evolving mechanisms for the well-studied catalysts are illustrated. In addition, several molecular catalyst-modified electrodes for hydrogen production are described.
459 citations
TL;DR: In this paper, an equilibrium, commercial diluted ZSM-5 catalyst was used as the base case, in comparison with a series of nickel (Ni) and cobalt (Co) modified variants at varying metal loading.
Abstract: The main objective of the present work was the study of different ZSM-5 catalytic formulations for the in situ upgrading of biomass pyrolysis vapors. An equilibrium, commercial diluted ZSM-5 catalyst was used as the base case, in comparison with a series of nickel (Ni) and cobalt (Co) modified variants at varying metal loading (1–10 wt.%). The product yields and the composition of the produced bio-oil were significantly affected by the use of all ZSM-5 catalytic materials, compared to the non-catalytic flash pyrolysis, producing less bio-oil but of better quality. Incorporation of transition metals (Ni or Co) in the commercial equilibrium/diluted ZSM-5 catalyst had an additional effect on the performance of the parent ZSM-5 catalyst, with respect to product yields and bio-oil composition, with the NiO modified catalysts being more reactive towards decreasing the organic phase and increasing the gaseous products, compared to the Co 3 O 4 supported catalysts. However, all the metal-modified catalysts exhibited limited reactivity towards water production, while simultaneously enhancing the production of aromatics and phenols. An interesting observation was the in situ reduction of the supported metal oxides during the pyrolysis reaction that eventually led to the formation of metallic Ni and Co species on the catalysts after reaction, which was verified by detailed XRD and HRTEM analysis of the used catalysts. The Co 3 O 4 supported ZSM-5 catalysts exhibited also a promising performance in lowering the oxygen content of the organic phase of bio-oil.
446 citations
TL;DR: The biological functions of Cobalt are updated in the light of recent understanding of cobalt interference with the sensing in almost all animal cells of oxygen deficiency (hypoxia), and some of the toxic effects of cobALT (Co(2+)) have recently been proposed to be due to putative inhibition of Ca(2+) entry and Ca( 2+)-signaling and competition with Ca(3+)-binding proteins.
TL;DR: The facile synthesis of nickel cobalt layered double hydroxides (LDHs) on conducting Zn(2)SnO(4) (ZTO) and the application of this material to a supercapacitor is reported and the first report of an enhancement of the active faradic reaction sites (electroactive sites) resulting from the heterostructure is presented.
Abstract: Conducting nanowires are of particular interest in energy-related research on devices such as supercapacitors, batteries, water splitting electrodes and solar cells. Their direct electrode/current collector contact and highly conductive 1D structure enable conducting nanowires to provide ultrafast charge transportation. In this paper, we report the facile synthesis of nickel cobalt layered double hydroxides (LDHs) on conducting Zn2SnO4 (ZTO) and the application of this material to a supercapacitor. This study also presents the first report of an enhancement of the active faradic reaction sites (electroactive sites) resulting from the heterostructure. This novel material demonstrates outstanding electrochemical performance with a high specific capacitance of 1805 F g−1 at 0.5 A g−1, and an excellent rate performance of 1275 F g−1 can be achieved at 100 A g−1. Furthermore, an asymmetric supercapacitor was successfully fabricated using active carbon as a negative electrode. This asymmetric device exhibits a high energy density of 23.7 W h kg−1 at a power density of 284.2 W kg−1. Meanwhile, a high power density of 5817.2 W kg−1 can be achieved at an energy density of 9.7 W h kg−1. More importantly, this device exhibits long-term cycling stability, with 92.7% capacity retention after 5000 cycles.
TL;DR: This work presents a highly active photocatalyst for visible-light-driven water oxidation, consisting of single-crystalline meso- and macroporous LaTiO(2)N (LTON) with a band gap of 2.1 eV, and earth-abundasnt cobalt oxide (CoO(x)) as a cocatalyst.
Abstract: Highly efficient water oxidation utilizing visible photons of up to 600 nm is a crucial step in artifical photosynthesis. Here we present a highly active photocatalyst for visible-light-driven water oxidation, consisting of single-crystalline meso- and macroporous LaTiO2N (LTON) with a band gap of 2.1 eV, and earth-abundasnt cobalt oxide (CoOx) as a cocatalyst. The optimized CoOx/LTON had a high quantum efficiency of 27.1 ± 2.6% at 440 nm, which substantially exceeds the values reported for previous particulate photocatalysts with a 600-nm absorption edge.
TL;DR: An environmentally compatible process based on vacuum pyrolysis, oxalate leaching and precipitation is applied to recover cobalt and lithium from spent lithium-ion batteries and the combined process is simple and adequate for the recovery of valuable metals.
TL;DR: An asymmetric supercapacitor with high energy and power densities has been successfully assembled based on NiCo2O4-reduced graphite oxide composite material and activated carbon as discussed by the authors.
Abstract: In this contribution, we report a facile preparation method of nickel cobalt oxide–reduced graphite oxide (NiCo2O4–rGO) composite material. A fast Faradic process has been realized by sodium dodecyl sulfate (SDS)-induced ultrasmall NiCo2O4 nanocrystals on rGO. As a result, this composite material gives a high specific capacitance of 1222 F g−1 at 0.5 A g−1 and 768 F g−1 at 40 A g−1, showing an outstanding rate capability. An asymmetric supercapacitor device with high energy and power densities has been successfully assembled based on NiCo2O4–rGO composite material and activated carbon. The optimized device shows a high energy density of 23.32 Wh kg−1 at a power density of 324.9 W kg−1. In addition, this asymmetric device shows good stability towards multistage current charge–discharge cycles.
TL;DR: In this article, the performance of catalytic catalytic hydrodeoxygenation of guaiacol was studied over Fe/SiO2 as a model reaction of lignin pyrolysis vapours hydrotreatment.
Abstract: Lignin could be an important green source for aromatic hydrocarbon production (benzene, toluene and xylenes, BTX). Catalytic hydrodeoxygenation (HDO) of guaiacol was studied over Fe/SiO2 as a model reaction of lignin pyrolysis vapours hydrotreatment. The catalytic conditions were chosen to match with the temperature of never-condensed lignin pyrolysis vapours. The catalyst was characterised by XRD, Mossbauer spectroscopy, N2 sorption and temperature programmed oxidation. A comparison is made with a commercial cobalt-based catalyst. Cobalt-based catalyst shows a too high production of methane. Fe/SiO2 exhibits a good selectivity for BT production. It does not catalyse the aromatic ring hydrogenation. Temperature (623–723 K) and space time (0.1–1.5 gcat h/gGUA) influence the aromatic carbon–oxygen bond hydrogenolysis reaction whereas H2 partial pressure (0.2–0.9 bar) has a minor influence. 38% of BT yield was achieved under the best investigated conditions. Reaction mechanisms for guaiacol conversion over Fe/SiO2 are discussed.
TL;DR: In this paper, a facile synthesis of highly conductive nickel cobalt oxide-single wall carbon nanotube (NiCo2O4-SWCNT) nanocomposite by controlled hydrolysis process in ethanol-water mixed solvent is reported.
Abstract: The electron conductivity of electrode material has always been a problem that hinders the practical application of supercapacitor. In this contribution, we report a facile synthesis of highly conductive nickel cobalt oxide-single wall carbon nanotube (NiCo2O4–SWCNT) nanocomposite by controlled hydrolysis process in ethanol–water mixed solvent. Ultrafine NiCo2O4 nanocrystals with a diameter around 6–10 nm are formed on the functionalized SWCNT bundles. This novel material not only exhibits a high specific capacitance of 1642 F g–1 within a 0.45 V potential range but also shows an excellent cycling stability of 94.1% retention after 2000 cycles at high mass loading. Our method provides a promising facile and high-performance strategy for supercapacitor electrode application.
TL;DR: Two diimine-dioxime complexes were identified as exhibiting catalytic onset at comparatively low overpotentials relative to other reported homogeneous cobalt and nickel electrocatalysts in aqueous solution.
Abstract: A series of water-soluble molecular cobalt complexes of tetraazamacrocyclic ligands are reported for the electrocatalytic production of H2 from pH 2.2 aqueous solutions. The comparative data reported for this family of complexes shed light on their relative efficiencies for hydrogen evolution in water. Rotating disk electrode voltammetry data are presented for each of the complexes discussed, as are data concerning their respective pH-dependent electrocatalytic activity. In particular, two diimine–dioxime complexes were identified as exhibiting catalytic onset at comparatively low overpotentials relative to other reported homogeneous cobalt and nickel electrocatalysts in aqueous solution. These complexes are stable at pH 2.2 and produce hydrogen with high Faradaic efficiency in bulk electrolysis experiments over time intervals ranging from 2 to 24 h.
TL;DR: In this paper, two different techniques (precipitation with ammonia and hydrothermal synthesis with ethylene glycol, both followed by autoclave aging) were employed for the synthesis of CeO2-ZrO2 mixed oxides on a 80-20-wt.% basis.
Abstract: Two different techniques (precipitation with ammonia and hydrothermal synthesis with ethylene glycol, both followed by autoclave aging) were employed for the synthesis of CeO2–ZrO2 mixed oxides on a 80–20 wt.% basis. Aging parameters, such as time and temperature, were systematically investigated in order to determine the optimal conditions to maintain high surface area and oxygen mobility of the prepared solids. Different loadings of nickel and cobalt (3, 6, 12 and 18 wt.%) were subsequently deposited via homogeneous deposition precipitation method. Calcined bimetallic catalysts were characterized by N2 adsorption–desorption, XRD, H2-TPR, TPO-TGA and FE-SEM methods, and tested for activity, selectivity and stability in the reforming of equimolar CH4–CO2 gas streams. During temperature programmed methane reforming tests, syngas with a H2/CO ratio between 0.3 and 0.79 was produced. Growth of carbon nanofilaments over the catalyst does not lead to deactivation, but can cause reactor plugging. Two conditions are vital and must be fulfilled simultaneously to avoid excessive carbon deposition: strong interaction between the NiCo bimetallic particles and CeZr support, which exists only at NiCo loadings up to 6 wt.%, as well as high oxygen mobility within the highly defective CeO2–ZrO2 crystalline lattice for timely carbon oxidation.
TL;DR: A pseudotetrahedral cobalt(II) complex with a positive axial zero-field splitting parameter of D = 12.7 cm(-1), as determined by high-field EPR spectroscopy, is shown to exhibit slow magnetic relaxation under an applied dc field.
TL;DR: Enantiopure C(1)-symmetric bis(imino)pyridine cobalt chloride, methyl, hydride, and cyclometalated complexes are active as catalysts for the enantioselective hydrogenation of geminal-disubstituted olefins.
Abstract: Enantiopure C1-symmetric bis(imino)pyridine cobalt chloride, methyl, hydride, and cyclometalated complexes have been synthesized and characterized. These complexes are active as catalysts for the enantioselective hydrogenation of geminal-disubstituted olefins.
TL;DR: A series of cobalt dithiolene complexes are reported that are exceptionally active for the catalytic reduction of protons in aqueous solvent mixtures and represent a new group of active catalysts for the reduction of Protons.
Abstract: Artificial photosynthesis (AP) is a promising method of converting solar energy into fuel (H(2)). Harnessing solar energy to generate H(2) from H(+) is a crucial process in systems for artificial photosynthesis. Widespread application of a device for AP would rely on the use of platinum-free catalysts due to the scarcity of noble metals. Here we report a series of cobalt dithiolene complexes that are exceptionally active for the catalytic reduction of protons in aqueous solvent mixtures. All catalysts perform visible-light-driven reduction of protons from water when paired with Ru(bpy)(3)(2+) as the photosensitizer and ascorbic acid as the sacrificial donor. Photocatalysts with electron withdrawing groups exhibit the highest activity with turnovers up to 9,000 with respect to catalyst. The same complexes are also active electrocatalysts in 11 acetonitrile/water. The electrocatalytic mechanism is proposed to be ECEC, where the Co dithiolene catalysts undergo rapid protonation once they are reduced to CoL(2)(2-). Subsequent reduction and reaction with H(+) lead to H(2) formation. Cobalt dithiolene complexes thus represent a new group of active catalysts for the reduction of protons.
TL;DR: Nickel-Cobalt bimetallic hydroxide catalysts, synthesized through a one-step electrodeposition method, were evaluated for the oxidation of urea in alkaline conditions with the intention of reducing the oxidation overpotential for this reaction as discussed by the authors.
TL;DR: In this paper, a recent technology of methane dry reforming over cobalt metal-base catalyst, covering the catalyst activity and their resistance of catalyst deactivation, is presented, which is a recent development.
Abstract: Dry reforming of methane produces syngas with desirable H2/CO ratio. Besides noble metal catalysts, the cobalt catalyst performs good activity in this reaction. However, carbon deposition and catalyst deactivation are becoming the main problems inhibiting the scale up of this process into industrial application. Recently, many scientists were trying to increase the activity as well as the stability toward coking by using variants of support, promoter, and combination of metal series catalyst. This paper presents a recent technology of methane dry reforming over cobalt metal-base catalyst, covering the catalyst activity and their resistance of catalyst deactivation.
TL;DR: In this paper, X-ray diffraction analysis, Fourier Transform Infrared (FTIR) and Vibrating Sample Magnetometer were carried out at room temperature to study the structural and magnetic properties of cobalt ferrite nanoparticles.
TL;DR: The synthesis and behaviour of novel cobalt dihydrogen complexes that show improved catalyst performance for the catalytic hydrogenation of CO2 are described.
Abstract: the potential to replace the use of the more toxic carbon monoxide, which is currently utilised in industry on a million-ton scale. In the last 20 years, significant improvements in catalyst development have been made in this area, starting from ruthenium complexes by Leitner and progressing to the recent work of Nozaki and co-workers that uses highly efficient pincer-type Ir catalysts. So far, mainly noble metal complexes based on ruthenium, rhodium and iridium have been studied for this transformation and impressive catalyst productivities have been achieved. On the other hand, non-precious-metal catalysts based on iron, manganese or zinc have scarcely been investigated and the obtained catalytic activities are low (turnover numbers (TONs)< 120). In addition to the hydrogenation of carbon dioxide, the catalytic reduction of bicarbonates and carbonates also provides an interesting route for the synthesis of formates. To date, relatively few transition-metal catalysts have been developed for this biologically relevant reduction (Scheme 2). For several years, we have been exploring the use of iron catalysts for various redox reactions. For example, we were recently able to show that the hydrogenation of CO2 and bicarbonates is possible by using iron complexes with the socalled tetraphos ligand (PP3: P(CH2CH2PPh2)3). [10] The turnover numbers with this iron system (600–700) are still much lower than those of the best precious-metal catalysts, but it was the first real step forward for the use of non-precious metals for the benign reduction of CO2. Herein, we describe the synthesis and behaviour of novel cobalt dihydrogen complexes that show improved catalyst performance for the catalytic hydrogenation of CO2. To the best of our knowledge, homogeneous cobalt complexes have scarcely been reported for this type of transformation. However, the use of a cobalt foil at high temperature (250 8C) has been reported to produce some activity. In addition, CoACHTUNGTRENNUNG(OAc)2 has been used for hydrogenation in the presence of phosphane ligands. This limited data is somewhat surprising considering the recent interest in cobalt dihydrogen complexes. Based on our previous work on iron complexes, we started to investigate the hydrogenation of sodium bicarbonate by using in situ generated catalysts. Initially, we used a sodium bicarbonate solution containing cationic CoACHTUNGTRENNUNG(BF4)2·6H2O and PP3 at 80 8C. To our delight, after 20 h, sodium formate was obtained in 94 % yield, and a turnover number (TON) of 3877 when the reaction temperature was increased to 120 8C (Table 1, entries 1 and 2). This catalytic productivity is six times as high as the best TON described in the literature for any non-precious-metal catalyst, and twice that of the best precious-metal system described. Notably, the catalytic activity is uniquely dependent on the PP3 ligand. In tests with various other ligands, such as triphenylphosphine, xantphos, 1,2-bisdiphenylphosphinoethane, [18]crown-6 and 1,1,1-tris(diphenylphosphinomethyl)ethane, no activity was observed. However, variation of the cobalt precursor is possible and several cobalt species, for example, CoACHTUNGTRENNUNG(acac)2 (acac=acetylacetonate), CoACHTUNGTRENNUNG(acac)3 and CoCl2, in the presence of the tetraphos ligand showed similar activity to the cationic cobalt salts. Utilising the in situ generated active cobalt complex also made it possible to hydrogenate sodium bicarbonate at a lower pressure of hydrogen (5 bar; Table 1, entry 3). [a] C. Federsel, C. Ziebart, Dr. R. Jackstell, Dr. W. Baumann, Prof. Dr. M. Beller Leibniz-Institut f r Katalyse e.V. an der Universit t Rostock Albert Einstein Str. 29a, 18059 Rostock (Germany) Fax: (+49) 381-1281-51113 E-mail : matthias.beller@catalysis.de Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201101343. Scheme 1. Catalytic hydrogenation of CO2 to form alkyl formates and formamides. Scheme 2. Cobalt-catalysed hydrogenation of bicarbonates to form formates.
TL;DR: A new cobalt(I) complex is reported that reacts with tosylic acid to evolve hydrogen with a driving force of just 30 meV/Co, and analysis of the kinetics suggests that CoIII-H produces hydrogen by two competing pathways: a slower homolytic route involving two Co III-H species and a dominant heterolytic channel.
Abstract: Several cobalt complexes catalyze the evolution of hydrogen from acidic solutions, both homogeneously and at electrodes. The detailed molecular mechanisms of these transformations remain unresolved, largely owing to the fact that key reactive intermediates have eluded detection. One method of stabilizing reactive intermediates involves minimizing the overall reaction free-energy change. Here, we report a new cobalt(I) complex that reacts with tosylic acid to evolve hydrogen with a driving force of just 30 meV/Co. Protonation of CoI produces a transient CoIII-H complex that was characterized by nuclear magnetic resonance spectroscopy. The CoIII-H intermediate decays by second-order kinetics with an inverse dependence on acid concentration. Analysis of the kinetics suggests that CoIII-H produces hydrogen by two competing pathways: a slower homolytic route involving two CoIII-H species and a dominant heterolytic channel in which a highly reactive CoII-H transient is generated by CoI reduction of CoIII-H.
TL;DR: This work presents an oxyhydride of the perhaps most well-known perovskite, BaTiO(3), as an O(2-)/H(-) solid solution with hydride concentrations up to 20% of the anion sites, which is electronically conducting, and stable in air and water at ambient conditions.
Abstract: In oxides, the substitution of non-oxide anions (F(-),S(2-),N(3-) and so on) for oxide introduces many properties, but the least commonly encountered substitution is where the hydride anion (H(-)) replaces oxygen to form an oxyhydride. Only a handful of oxyhydrides have been reported, mainly with electropositive main group elements or as layered cobalt oxides with unusually low oxidation states. Here, we present an oxyhydride of the perhaps most well-known perovskite, BaTiO(3), as an O(2-)/H(-) solid solution with hydride concentrations up to 20% of the anion sites. BaTiO(3-x)H(x) is electronically conducting, and stable in air and water at ambient conditions. Furthermore, the hydride species is exchangeable with hydrogen gas at 400 °C. Such an exchange implies diffusion of hydride, and interesting diffusion mechanisms specific to hydrogen may be at play. Moreover, such a labile anion in an oxide framework should be useful in further expanding the mixed-anion chemistry of the solid state.