Cobalt Oxide Clusters Research Articles

Local spin moment of LaCoO 3 probed by a core hole

The electronic structures of the ground state and the 1s −1 core-hole state of high-spin cobalt oxide clusters are calculated. The calculated results indicate that the high-spin Co 3+ oxide becomes low spin in the core-hole state. To check the validity of the present calculation, we have measured the high-resolution X-ray fluorescence spectra of the Co K–L 3 (Kα 1) line shape for various cobalt compounds using a double-crystal X-ray fluorescence spectrometer: Co(acac) 2, Co(acac) 3, CoF 3, CoCl 2, CoBr 2, K 3[Co(CN) 6], CoO, Co 3O 4, LaCoO 3, and Co (metal), where acac denotes CH 3COCHCOCH 3 −. We conclude from the comparison of the calculations with the experimental results that the cobalt ion in LaCoO 3 at room temperature is high-spin state in spite that the reported spin state of this perovskite is different among the probing methods. The implications of the spin-flip shake-down process for the interpretation of the core-level X-ray photoelectron spectra, X-ray absorption spectra, and X-ray fluorescence spectra are discussed.

Preparation and characterization of cobalt oxide nanosized particles obtained by an electrochemical method

An electrochemical process has been described by which metal foils are anodically dissolved and the metal salts formed as intermediates are cathodically reduced with formation of metal clusters stabilized by tetraalkylammonium salts. The electrolysis process has been investigated by cyclic voltammetry showing the formation of reduced cobalt adatoms followed by cluster formation. In the present paper we have studied such process for the preparation of nanosized Co clusters and their ulterior oxidation to cobalt oxide nanosized particles stable in air. The TEM analysis shows the formation of homogeneous particles (2–4 nm in diameter) embedded in a surfactant protective matrix. Electron diffraction shows broad but clear peaks corresponding to the formation of very small CoO crystallites. X-Ray Absorption (XAS), Electron Energy Loss (EELS) and X-Ray Photoelectron (XPS) spectroscopies have been used to characterize the materials showing the stabilization of small cobalt oxide clusters.

T.p.r. study on hydrolysis character of Co 2+ ions in Y zeolite

The Co2+ ion-exchanged Y zeolites treated with NaOH or ammonia solution at various pH values were investigated by the temperature-programmed reduction (t.p.r.) technique. A significant hydrolysis of the Co2+ ions was induced by NaOH treatment above pH 10.5, accompanying the migration of the Co2+ ions inside the sodalite cages and hexagonal prisms. Two kinds of cobalt oxide species were formed for NaOH-treated CoY above pH 10.7, followed by calcination in air: aggregated Co3O4-like species outside the zeolite cages and small cobalt oxide cluster inside the cages, respectively. The formation of Co3O4-like species was facilitated by treatment at high pH region in contrast to the case for the hydrolysis of NiY.

The role of cluster ion structure in reactivity and collision-induced dissociation: Application to cobalt/oxygen cluster ions in the gas phase

Ion/molecule reaction products of cobalt cluster ions have been characterized using mass spectrometric techniques. Atomic and bare-metal cluster ions were desorbed from foils by particle bombardment within a high-pressure (0.1–0.2 Torr) ion source. Sputtered metal cluster ions react with O2 to produce abundant stoichiometric or nearly stoichiometric cobalt(II) oxide cluster ions. The positive cluster product ions consist of three types: oxygen-deficient [Co(CoO)x]+ clusters, oxygen-equivalent [(CoO)x]+ clusters, and (in less abundance) metal-deficient [(CoO)xO]+ clusters. Tandem mass spectrometry and collision spectroscopy provide structural information about the more abundant cobalt cluster product ions. A major collision-induced fragmentation pathway for the oxygen-equivalent [(CoO)x]+ clusters is the loss of a CoO moiety to form [(CoO)x−1]+ fragments. A major collision-induced fragmentation pathway for the oxygen-deficient [Co(CoO)x]+ clusters is the loss of a cobalt atom to yield [(CoO)x]+ fragments. Geometric structures of the cobalt/oxygen cluster ions were calculated using a Coulomb plus Born–Mayer pair-potential model. The oxygen-equivalent cluster structures were found to be ‘‘globular’’ cages, rings, or ladders. The oxygen-deficient cluster structures were found to be strained and ‘‘angular’’ with protruding cobalt atoms. The structures are discussed in terms of the observed collision-induced fragmentations. The fragmentations are rationalized using an ‘‘instantaneous’’ dissociation model of the collision-induced dissociation of the cluster ions. Preliminary trajectory calculations using classical dynamics support the use of this instantaneous dissociation model. The role of cluster ion structure in reactivity and collision-induced dissociation is discussed in terms of the experimental data and theoretical structures.