Cobalt

About: Cobalt is a research topic. Over the lifetime, 69899 publications have been published within this topic receiving 1242058 citations. The topic is also known as: Co & Element 27.

Electrocatalytic reduction of carbon dioxide by using macrocycles of nickel and cobalt

Abstract: An indirect method for the reduction of CO/sub 2/ in nonaqueous solutions and involving initial reduction of metal complexes and their subsequent reduction with CO/sub 2/ is described. The complexes were tetraazamacrocyclic complexes of Ni and Co. The catalytic reduction process was investigated by means of controlled potential coulometry experiments performed in a gas-tight electrolysis cell under a CO/sub 2/ atmosphere. The effects of water, Ar, and N/sub 2/ on the electrolysis process were investigated. The results indicated that the indirect electrochemical reduction of CO/sub 2/ occurred at a potential between -1.3 and -1.6V vs SCE and that the reduction was indeed catalyzed by the metal complexes. Reaction periods of as long as 24 h did not reduce catalytic activity; and in most cases, the catalyst was isolated in its original form at the end of the run. A protic source was found to be necessary for the reaction to yield CO and H/sub 2/; and in the absence of a protic source, simple stoichiometric reduction of the complex was noted. (BLM)

Chemical effects at metal/oxide interfaces studied by x-ray-absorption spectroscopy

Abstract: A chemical and magnetic characterization of ferromagnet/antiferromagnet interfaces is essential to understand the microscopic origins of exchange anisotropy and other magnetic phenomena. We have used high-resolution L-edge x-ray absorption spectroscopy (XAS), which is element specific and sensitive to chemical environment and spin orientation, to investigate the interface of antiferromagnetic oxides with ferromagnetic metals. Clear quantitative evidence of oxidation/reduction reactions at the as-grown metal/oxide interface is presented. In situ-- and ex situ--grown samples of the form oxide $(5--30 \AA{})/\mathrm{metal}$ $(1--10 \AA{}),$ where oxide is either NiO or CoO and metal is either Fe, Co, or Ni, were studied by high-resolution XAS. For all samples, a metal(oxide) layer adjacent to an oxide(metal) layer was partially oxidized(reduced). Quantitative analysis of the spectra showed that one to two atomic layers on either side of the interface were oxidized/reduced. An elemental series of samples showed that the amount of oxidation/reduction was in accord with the difference in oxidation potentials of the adjacent cations, e.g., oxide layers were more strongly reduced by an iron metal layer than by cobalt or nickel metal layers. Annealing to temperatures, typically used to bias devices, was shown to significantly increase the amount of oxidation/reduction. The oxidation behavior of iron was shown to depend on the amount of oxygen available. Our results are believed to provide important information for the improved understanding of exchange anisotropy.

Iron- and Cobalt-Catalyzed Alkene Hydrogenation: Catalysis with Both Redox-Active and Strong Field Ligands

Abstract: ConspectusThe hydrogenation of alkenes is one of the most impactful reactions catalyzed by homogeneous transition metal complexes finding application in the pharmaceutical, agrochemical, and commodity chemical industries. For decades, catalyst technology has relied on precious metal catalysts supported by strong field ligands to enable highly predictable two-electron redox chemistry that constitutes key bond breaking and forming steps during turnover. Alternative catalysts based on earth abundant transition metals such as iron and cobalt not only offer potential environmental and economic advantages but also provide an opportunity to explore catalysis in a new chemical space. The kinetically and thermodynamically accessible oxidation and spin states may enable new mechanistic pathways, unique substrate scope, or altogether new reactivity. This Account describes my group’s efforts over the past decade to develop iron and cobalt catalysts for alkene hydrogenation. Particular emphasis is devoted to the inter...

Hollow N-Doped Carbon Spheres with Isolated Cobalt Single Atomic Sites: Superior Electrocatalysts for Oxygen Reduction.

Abstract: The search for a low-cost, ultrastable, and highly efficient non-precious metal catalyst substitute for Pt in the oxygen reduction reaction (ORR) is extremely urgent, especially in acidic media. Herein, we develop a template-assisted pyrolysis (TAP) method to obtain a unique Co catalyst with isolated single atomic sites anchored on hollow N-doped carbon spheres (ISAS-Co/HNCS). Both the single sites and the hollow substrate endow the catalyst with excellent ORR performance. The half-wave potential in acidic media approaches that of Pt/C. Experiments and density functional theory have verified that isolated Co sites are the source for the high ORR activity because they significantly increase the hydrogenation of OH* species. This TAP method is also demonstrated to be effective in preparing a series of ISAS-M/HNCS, which provides opportunities for discovering new catalysts.