Showing papers on "Cobalt published in 2009"
TL;DR: Nanostructured Co(3)O(4) clusters in mesoporous silica are the first example of a nanometer-sized multielectron catalyst made of a first-row transition-metal oxide that evolves oxygen from water efficiently.
Abstract: Light, inexpensive, effective: Nanostructured Co(3)O(4) clusters (see picture) in mesoporous silica are the first example of a nanometer-sized multielectron catalyst made of a first-row transition-metal oxide that evolves oxygen from water efficiently. The nanorod bundle structure of the catalyst results in a very large surface area, an important factor contributing to the high turnover frequency.
715 citations
TL;DR: The origin of the cobalt particle size effects in Fischer-Tropsch (FT) catalysis was studied and the surface-specific activity (TOF) quantitatively and the CH(4) selectivity qualitatively as a function of Co particle size for the FT reaction was studied.
Abstract: The effects of metal particle size in catalysis are of prime scientific and industrial importance and call for a better understanding. In this paper the origin of the cobalt particle size effects in Fischer−Tropsch (FT) catalysis was studied. Steady-State Isotopic Transient Kinetic Analysis (SSITKA) was applied to provide surface residence times and coverages of reaction intermediates as a function of Co particle size (2.6−16 nm). For carbon nanofiber supported cobalt catalysts at 210 °C and H2/CO = 10 v/v, it appeared that the surface residence times of reversibly bonded CHx and OHx intermediates increased, whereas that of CO decreased for small (<6 nm) Co particles. A higher coverage of irreversibly bonded CO was found for small Co particles that was ascribed to a larger fraction of low-coordinated surface sites. The coverages and residence times obtained from SSITKA were used to describe the surface-specific activity (TOF) quantitatively and the CH4 selectivity qualitatively as a function of Co particl...
675 citations
TL;DR: Catalytic activity for O(2) generation in aqueous solutions containing 0.5 M NaCl is retained for catalysts grown from phosphate electrolyte, and methylphosphonate and borate electrolytes support catalyst activity comparable to that observed for phosphate.
Abstract: Electrolysis of Co2+ in phosphate, methylphosphonate, and borate electrolytes effects the electrodeposition of an amorphous highly active water oxidation catalyst as a thin film on an inert anode. Electrodeposition of a catalytically competent species immediately follows oxidation of Co2+ to Co3+ in solution. Methylphosphonate and borate electrolytes support catalyst activity comparable to that observed for phosphate. Catalytic activity for O2 generation in aqueous solutions containing 0.5 M NaCl is retained for catalysts grown from phosphate electrolyte.
584 citations
TL;DR: In this paper, a novel approach of using Fe-Co mixed oxide nanocatalysts for the heterogeneous activation of peroxymonosulfate (PMS) to generate sulfate radical-based advanced oxidation technologies (SR-AOTs) targeting the decomposition of 2,4-dichlorophenol, and especially focus on some synthesis parameters such as calcination temperature, Fe/Co contents, and TiO 2 support.
Abstract: Sulfate radical-based advanced oxidation technologies (SR-AOTs) are attracting considerable attention due to the high oxidizing ability of SRs to degrade organic pollutants in aqueous environments This study was carried out to respond to current concerns and challenges in SR-AOTs, including (i) need of heterogeneous activation of sulfate salts using transition metal oxides, (ii) nanoscaling of the metal oxide catalysts for high catalytic activity and promising properties with respect to leaching, and (iii) easy removal and recovery of the catalytic materials after their applications for water and wastewater treatments In this study, we report a novel approach of using Fe–Co mixed oxide nanocatalysts for the heterogeneous activation of peroxymonosulfate (PMS) to generate SRs targeting the decomposition of 2,4-dichlorophenol, and especially focus on some synthesis parameters such as calcination temperature, Fe/Co contents, and TiO 2 support The physicochemical properties of the catalysts were investigated using porosimetry, XRD, HR-TEM, H 2 -TPR, and XPS Ferromagnetic CoFe 2 O 4 composites formed by thermal oxidation of a mixed phase of Fe and Co exhibited significant implications for the efficient and environmentally friendly activation of PMS, including (i) the cobalt species in CoFe 2 O 4 are of Co(II), unlike Co 3 O 4 showing some detrimental effects of Co(III) on the PMS activation, (ii) CoFe 2 O 4 possesses suppressed Co leaching properties due to strong Fe–Co interactions (ie Fe–Co linkages), and (iii) Fe–Co catalysts in form of CoFe 2 O 4 are easier to recover due to the unique ferromagnetic nature of CoFe 2 O 4 In addition, the presence of Fe was found to be beneficial for enriching hydroxyl group content on the Fe–Co catalyst surface, which is believed to facilitate the formation of Co(II)-OH complexes that are vital for heterogeneous PMS activation
519 citations
TL;DR: In this article, the structural and magnetic properties of nanocrystalline manganese, cobalt, and nickel spinel ferrites dispersed in a highly porous SiO2 aerogel matrix were studied.
Abstract: The structural and magnetic properties of nanocrystalline manganese, cobalt, and nickel spinel ferrites dispersed in a highly porous SiO2 aerogel matrix were studied. X-ray diffraction and high-resolution transmission electron microscopy indicate that single crystalline ferrite nanoparticles are well dispersed in the amorphous matrix. The cation distribution between the octahedral and tetrahedral sites of the spinel structure was investigated by X-ray absorption spectroscopy. The analysis of both the X-ray absorption near edge structure and the extended X-ray absorption fine structure indicates that the degree of inversion of the spinel structure increases in the series Mn, Co, and Ni spinel, in accordance with the values commonly found in the corresponding bulk spinels. In particular, fitting of the EXAFS data indicates that the degree of inversion in nanosized ferrites is 0.20 for MnFe2O4, 0.68 for CoFe2O4, and 1.00 for NiFe2O4. Magnetic characterization further supports these findings.
420 citations
TL;DR: In this article, Alumina supported Ni, Co and bimetallic Ni-Co catalysts with 9% nominal metal content have been prepared, characterized and tested for the dry reforming of methane.
Abstract: Alumina supported Ni, Co and bimetallic Ni–Co catalysts (with 9 wt.% nominal metal content) have been prepared, characterized and tested for the dry reforming of methane. For catalysts characterization the following techniques have been used: Atomic Absorption Spectroscopy (ICP-AES), Transmission Electron Microscopy (TEM), Temperature Programmed Reduction (TPR-H2) and Temperature Programmed Oxidation (TPO). The dry reforming of methane was carried out at 973 K using a mixture CH4:CO2 (1:1). Among the catalysts studied, those with the highest cobalt content (Co(9) and NiCo(1–8)) are the most active and stable, but they produce a large amount of carbon. The higher activity exhibited by cobalt rich catalysts is related with the higher activity of this metal for methane decomposition, while their remarkable stability seems to be due to the presence of large particles involved in long-term conversion, because they produce non-deactivating carbon deposits.
364 citations
TL;DR: A new family of cobalt and nickel diimine-dioxime complexes are reported as efficient and stable electrocatalysts for hydrogen evolution from acidic nonaqueous solutions with slightly lower overvoltages and much larger stabilities towards hydrolysis as compared to previously reported cobaloxime catalysts.
Abstract: Hydrogen production through the reduction of water appears to be a convenient solution for the long-run storage of renewable energies. However, economically viable hydrogen production requests platinum-free catalysts, because this expensive and scarce (only 37 ppb in the Earth's crust) metal is not a sustainable resource [Gordon RB, Bertram M, Graedel TE (2006) Proc Natl Acad Sci USA 103:1209–1214]. Here, we report on a new family of cobalt and nickel diimine-dioxime complexes as efficient and stable electrocatalysts for hydrogen evolution from acidic nonaqueous solutions with slightly lower overvoltages and much larger stabilities towards hydrolysis as compared to previously reported cobaloxime catalysts. A mechanistic study allowed us to determine that hydrogen evolution likely proceeds through a bimetallic homolytic pathway. The presence of a proton-exchanging site in the ligand, furthermore, provides an exquisite mechanism for tuning the electrocatalytic potential for hydrogen evolution of these compounds in response to variations of the acidity of the solution, a feature only reported for native hydrogenase enzymes so far.
358 citations
TL;DR: The Co-TiO(2) catalyst synthesized in this work was found to be very effective in transforming ATZ as well as its intermediate in the presence of UV-vis irradiation.
351 citations
TL;DR: In this article, a series of 10%Co/ITQ-2 model catalysts have been prepared by combining a reverse micellar synthesis with a surface silylated ITQ 2 delaminated zeolite.
342 citations
TL;DR: In this paper, a novel process was conducted with experiments which separated and recovered metal values such as Co, Mn, Ni and Li from the cathode active materials of the lithium-ion secondary batteries.
326 citations
TL;DR: A survey of Arabidopsis accessions for ionomic phenotypes showed that truncation of FPN2 results in elevated shoot cobalt levels and leads to increased sensitivity to the metal, as well as in the fpn1 fpn2 double mutant, where cobalt cannot move to the shoot via FPN1 and is not sequestered in the root vacuoles via fPN2.
Abstract: Relatively little is known about how metals such as iron are effluxed from cells, a necessary step for transport from the root to the shoot. Ferroportin (FPN) is the sole iron efflux transporter identified to date in animals, and there are two closely related orthologs in Arabidopsis thaliana, IRON REGULATED1 (IREG1/FPN1) and IREG2/FPN2. FPN1 localizes to the plasma membrane and is expressed in the stele, suggesting a role in vascular loading; FPN2 localizes to the vacuole and is expressed in the two outermost layers of the root in response to iron deficiency, suggesting a role in buffering metal influx. Consistent with these roles, fpn2 has a diminished iron deficiency response, whereas fpn1 fpn2 has an elevated iron deficiency response. Ferroportins also play a role in cobalt homeostasis; a survey of Arabidopsis accessions for ionomic phenotypes showed that truncation of FPN2 results in elevated shoot cobalt levels and leads to increased sensitivity to the metal. Conversely, loss of FPN1 abolishes shoot cobalt accumulation, even in the cobalt accumulating mutant frd3. Consequently, in the fpn1 fpn2 double mutant, cobalt cannot move to the shoot via FPN1 and is not sequestered in the root vacuoles via FPN2; instead, cobalt likely accumulates in the root cytoplasm causing fpn1 fpn2 to be even more sensitive to cobalt than fpn2 mutants.
TL;DR: This analysis demonstrated that the formed carboxylate intermediate helped to stabilize the active Co(III) species against decomposition to inactive Co(II) by reversibly intramolecular Co-O bond formation and dissociation.
Abstract: The mechanism of the copolymerization of CO(2) and epoxides to afford the corresponding polycarbonates catalyzed by a highly active and thermally stable cobalt(III) complex with 1,5,7-triabicyclo[4,4,0] dec-5-ene (designated as TBD, a sterically hindered organic base) anchored on the ligand framework has been studied by means of electrospray ionization mass spectrometry (ESI-MS) and Fourier transform infrared spectroscopy (FTIR). The single-site, cobalt-based catalyst exhibited excellent activity and selectivity for polymer formation during CO(2)/propylene oxide (PO) copolymerization even at temperatures up to 100 degrees C and high [epoxide]/[catalyst] ratios, and/or low CO(2) pressures. The anchored TBD on the ligand framework plays an important role in maintaining thermal stability and high activity of the catalyst. ESI-MS and FTIR studies, in combination with some control experiments, confirmed the formation of the carboxylate intermediate with regard to the anchored TBD on the catalyst ligand framework. This analysis demonstrated that the formed carboxylate intermediate helped to stabilize the active Co(III) species against decomposition to inactive Co(II) by reversibly intramolecular Co-O bond formation and dissociation. Previous studies of binary catalyst systems based on Co(III)-Salen complexes did not address the role of these nucleophilic cocatalysts in stabilizing active Co(III) species during the copolymerization. The present study provides a new mechanistic understanding of these binary catalyst systems in which alternating chain-growth and dissociation of propagating carboxylate species derived from the nucleophilic axial anion and the nucleophilic cocatalyst take turns at both sides of the Co(III)-Salen center. This significantly increases the reaction rate and also helps to stabilize the active SalenCo(III) against decomposition to inactive SalenCo(II) even at low CO(2) pressures and/or relatively high temperatures.
TL;DR: In this paper, carbon-supported cobalt polypyrrole (Co-PPy/C) catalysts synthesized using a chemical method of polymerization synthesis were characterized using electrochemical techniques such as cyclic voltammetry (CV), rotating disk electrode (RDE), as well as rotating ring disk electrodes (RRDE) to quantitatively obtain the oxygen reduction reaction (ORR) kinetic constants and the reaction mechanisms.
TL;DR: In this article, a set of nanocrystalline cobalt oxide (Co 3 O 4 )-based catalysts have been prepared by means of an innovative soft reactive grinding (SRG) procedure.
TL;DR: In tandem: Employing a molecular dyad and a cobalt-based electrolyte gives a threefold-increase in open-circuit voltage for a p-type NiO device and a fourfold better energy conversion efficiency.
Abstract: Employing a mol. dyad and a cobalt-based electrolyte gives a threefold-increase in open-circuit voltage (VOC) for a p-type NiO device (VOC=0.35 V), and a fourfold better energy conversion efficiency. Incorporating these improvements in a TiO2/NiO tandem dye-sensitized solar cell (TDSC), results in a TDSC with a VOC=0.91 V.
TL;DR: In this article, the effect of oxygen mobility on the bio-ethanol steam reforming of ZrO2-supported cobalt catalysts was investigated, and it was found that the addition of ceria was found to improve the catalytic stability as well as activity.
TL;DR: In this paper, an epoxide addition procedure was used to synthesize high performance supercapacitors of the asymmetric type using cobalt oxide aerogels as the precursor.
Abstract: Mesoporous structures of high specific surface areas and high porosities, such as aerogels, are ideal for supercapacitor applications. This idea was successfully demonstrated for the first time by taking cobalt oxide aerogels as an example. Cobalt oxide aerogels of excellent supercapacitive properties, including high specific capacitances (the highest ever reported for cobalt oxides, >600 F/g at a high mass loading of 1 mg/cm2) and onset frequencies, and excellent reversibility and cycle stability, were successfully synthesized with an epoxide addition procedure by using cobalt nitrate as the precursor. The present development makes possible the low cost production of high performance supercapacitors of the asymmetric type.
TL;DR: The major reasons for carrying out electrodeposition in non-aqueous electrolytes (such as conventional organic solvents, ionic liquids and molten salts) are the water and air stability and the wide electrochemical window of these media.
TL;DR: The similarities in function and oxidative self-assembly of CoCF and the catalytic Mn complex in photosynthesis are striking and a close analogy is established with respect to the metal-oxo core of the catalyst.
Abstract: In photosynthesis, water is oxidized at a protein-bound Mn4Ca complex. Artificial water-oxidation catalysts that are similarly efficient and based on inexpensive and abundant materials are of great interest. Recently, assembly of a catalyst as an amorphous layer on inert cathodes by electrodeposition starting from an aqueous solution of cobalt ions and potassium phosphate has been reported. X-ray absorption spectroscopy on the cobalt catalyst film (CoCF) suggests that its central structural unit is a cluster of interconnected complete or incomplete CoIII−oxo cubanes. Potassium ligation to Co-bridging oxygens could result in Co3K(μ-O)4 cubanes, in analogy to the Mn3Ca(μ-O)4 cubane motif proposed for the photosynthetic Mn complex. The similarities in function and oxidative self-assembly of CoCF and the catalytic Mn complex in photosynthesis are striking. Our study establishes a close analogy also with respect to the metal−oxo core of the catalyst.
TL;DR: In this article, a bimetallic catalyst 7Ni3Co/LaAl was used for biogas reforming, and the results showed that the catalytic activity could be closely related to the Ni/Co ratio.
TL;DR: In 1938, Otto Roelen discovered that cobalt was able to catalyze specifically the hydrocarbonylation of ethylene, and homogeneous catalysis was born.
Abstract: In1938,whileOttoRoelenwasstudyingtheFischer-Tropsch reaction, which converts H2/CO into alkanes and alkenes, and was trying to improve the yields by recycling ethylene, the cobalt catalyst deposited on a ThO2/SiO2 support produced some propanal. Fortunately, Roelen focused on this unexpected reaction and discovered that cobalt was able to catalyze specifically the hydrocarbonylation of ethylene.1-3 It was rapidly established that this reaction, which has been extended to various alkenes, was occurring in the organic phase: homogeneous catalysis was born.
TL;DR: In this article, the state of the art related to the influence of cobalt particle size and cobalt phase composition, catalyst support and support texture, and promotion with noble metals on Fischer-Tropsch reaction rates, hydrocarbon selectivity and catalyst stability are discussed.
TL;DR: A series of cobalt-doped nickel ferrite with composition of Ni (1− x ) Co x Fe 2 O 4 with x ranges from 0.0 to 0.8 (in steps of 0.2) was prepared by using standard ceramic technique as discussed by the authors.
TL;DR: A series of one-electron outersphere cobalt bipyridyl redox couples were used as redox shuttles in dye-sensitized solar cells (DSSCs) as discussed by the authors.
Abstract: A series of one-electron outersphere cobalt bipyridyl redox couples were used as redox shuttles in dye-sensitized solar cells (DSSCs). Atomic layer deposition was used to deposit an ultrathin coating of alumina on nanoparticle-based TiO2 DSSC photoanodes, which results in significantly improved quantum yields for all of the DSSCs containing outersphere redox systems. However, a significant discrepancy in performance remains between DSSCs containing the different cobalt redox shuttles. Variation of the driving force for regeneration by ∼500 mV, by employing [Ru(bpy)2(4,4′-dicarboxy-bpy)](PF6)2 as a dye, combined with concentration dependence studies indicates that the cobalt redox couples are not limited by dye regeneration; however, in certain cases the iodide electrolyte was, one of the very few systems where alternate redox couples perform significantly better than triiodide/iodide. Electron lifetimes were measured with the open circuit voltage decay technique. The differences in the lifetimes (recombin...
TL;DR: In this paper, the formation of carbon deposits on samples of a Co/Pt/Al2O3 catalyst, taken from a 100-barrel/day slurry bubble column reactor operated over a period of 6 months at commercially relevant FTS conditions is reported.
Abstract: Deactivation of cobalt-based Fischer–Tropsch synthesis (FTS) catalysts by carbonaceous species has been previously postulated. This mechanism, however, is difficult to prove due to the presence of long chain hydrocarbon wax product and the potential accumulation of inactive carbon on the catalyst support. Furthermore, due to the slow build-up of low quantities of inactive carbon with time on stream, the investigation of carbon deposition necessitates the use of data from extended FTS runs. In this study, the formation of carbon deposits on samples of a Co/Pt/Al2O3 catalyst, taken from a 100-barrel/day slurry bubble column reactor operated over a period of 6 months at commercially relevant FTS conditions is reported. The spent catalysts were wax extracted in an inert environment and the amount, nature and location of carbon deposits were then studied using temperature programmed hydrogenation and oxidation (TPH/TPO), energy filtered transmission electron microscopy (EFTEM), high sensitivity low energy ion scattering (HS-LEIS) and hydrogen chemisorption. TPH/TPO showed that there is an increase in polymeric carbon with time on stream which may account for a part of the observed long-term catalyst deactivation. Carbon maps from EFTEM as well HS-LEIS data show that the polymeric carbon is located both on the alumina support and cobalt. Although there is clearly an interplay of various deactivation mechanisms which may also include sintering, poisoning and cobalt reconstruction, the evidence presented shows that the polymeric carbon on the metal may be linked with a part of the longer term catalyst deactivation.
Patent•
20 Jul 2009TL;DR: In this paper, a process for the selective production of ethanol by vapor phase reaction of acetic acid over a hydrogenating catalyst composition to form ethanol is disclosed and claimed, and an embodiment of this reaction is presented.
Abstract: A process for the selective production of ethanol by vapor phase reaction of acetic acid over a hydrogenating catalyst composition to form ethanol is disclosed and claimed. In an embodiment of this invention reaction of acetic acid and hydrogen over either cobalt and palladium supported on graphite or cobalt and platinum supported on silica selectively produces ethanol in a vapor phase at a temperature of about 25O0C.
TL;DR: In this article, the influence of different synthesis conditions on the combustion process, phase composition, textural and morphological properties is studied in detail by X-ray diffraction, nitrogen adsorption and scanning electron microscopy.
Abstract: Citrate–nitrate auto-combustion synthesis is used to prepare an iron, a cobalt and a cerium-perovskite. The influence of different synthesis conditions on the combustion process, phase composition, textural and morphological properties is studied in detail by X-ray diffraction, nitrogen adsorption and scanning electron microscopy. Results show that the combustion intensity increases from iron, to cerium, to cobalt-perovskite. Conversely, the combustion intensity decreases and thus the safety and the gain of the combustion process increase by using high fuel/oxidant ratios, low pH values or combustion reactors with high heat dispersion capacity. High fuel/oxidant ratios increase particle size and may enhance dopant segregation. Low citric acid/metal nitrates ratios may cause precipitation of the most insoluble compounds or segregation of the dopant. High citric acid/metal nitrates ratios increase the formation temperature of the perovskite-type structure. Low pH values are deleterious for the phase composition and/or for the morphology of the final product, although at high pH values dopant segregation may occur.
TL;DR: In this paper, a comparative study of the electrochemical stability of Pt 25 Cu 75 and Pt 20 Cu 20 Co 60 nanoparticle electrocatalysts in liquid electrolyte half-cell environment was conducted.
TL;DR: In this article, the structural, morphological and magnetic properties of the products were determined by X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), respectively.
TL;DR: In this article, a review of the application of solvent extraction for treating leach solutions is presented, where solvent extraction is used to extract valuable metals from spent hydrodesulphurization catalysts, such as molybdenum and vanadium.