Methane Reforming with Carbon Dioxide on the Co/α-Al2O3 Catalyst: The Formation, State, and Transformations of Surface Carbon

The interactions of oxidized and reduced Co/-Al₂O₃ (4 wt % CoO) with H₂, CH₄, CO₂, and O₂ and their mixtures are studied in flow and pulse regimes using a setup involving a DSC-111 differential scanning calorimeter and a system for chromatographic analyses. It is shown that treatment with hydrogen at 700°C results in the partial reduction of cobalt oxide to Co. Methane poorly reacts with the oxidized catalyst but readily reacts with the reduced catalyst to form H₂ and surface carbon. The initial surface carbon transforms into other forms, which block the cobalt surface to different extents and differ in the heats of reaction with CO₂. Carbon dioxide may react with the surface carbon to form CO (rapidly) and with metallic Co to form CO and CoO (slowly). Thus, the main route of methane reforming with carbon dioxide on Co/-Al₂O₃ is the dissociative adsorption of CH₄ to form surface carbon and H₂ and the reaction of surface carbon with CO₂ to form CO via the reverse Boudouard reaction.     

Rates of Dissociative Ionic Reactions in Aqueous Mixtures Correlated with Opposing Gibbs Energies of Transfer of Single Ions: Solvolysis of Chloropentacyanocobaltate(III) Anions in Water + Ethanol and Water + Urea

The kinetics of the solvolysis of Co(CN)₅Cl^3– have been investigated in water with an added structure former, ethanol, and with added urea, which has only a weak effect on the solvent structure. As this solvolysis involves a rate-determining dissociative step corresponding closely to a 100%; separation, Co³⁺ Cl^-, in the transition state, a Gibbs energy cycle relating Gibbs energies of activation in water and in the mixtures to Gibbs energies of transfer of individual ionic species between water and the mixtures, G _t ^o (i), can be applied. The acceleration of the reaction found with both these cosolvents results from the compensation of the retarding positive G _t ^o (Cl^- by the negative term [G _t ^o [Co(CN) ₅ ^2- ]-G _t ^o [Co(CN)₅Cl^3- arising from G _t ^o [Co(CN)₅Cl^3-]> G _t ^o [Co(CN) ₅ ^2- ]. Moreover, only a small tendency to extrema in the enthalpies and entropies of activation is found with both these cosolvents, as was also found with added methanol or ethane-1,2-diol, but unlike the extrema found when hydrophobic alcohols are added to water. With the latter, much greater negative values for G _t ^o [Co(CN) ₅ ^2- ]- _t ^o [Co(CN)₅Cl^3-] are found. When G G _t ^o [Co(CN) ₅ ^2- ]-G G _t ^o [CO(CN)₅Cl^3-] becomes low enough not to compensate for the positive G _t ^o (Cl^-), as with added hydrophilic glucose, the reaction is retarded. Compensating contributions of the various G _t ^o (i) involved in the Gibbs energy cycle with added methanol or ethane-1, 2-diol allow log (rate constant) to vary linearly with the reciprocal of the relative permittivity of the medium.     

Studies on mixed ligand complexes,part 5. Heterochelate complexes of cobalt(III) derived from the quadridentate NNNN donor ligand triethylenetetramine and bidentate OO,ON and NN donor ligands

Summary A series of new cobalt(III) complexes of general formula [Co(AA)(trien)]X_n (where AA = tropolone, acetoacetanilide, ethylacetoacetate, biguanide, 2-guanidinobenzimidazole, propylenediamine, picolylamine, 2,2-dipyridyl, 3-aminopyridine, picolinic acid and quinaldinic acid, trien = triethylenetetramine, X=Cl^–, Br^–, I^– and n=2–3) have been synthesized and characterized by elemental analysis, electronic and i.r. spectra, equivalent weight, conductance and magnetic measurements. The electronic spectra of the complexes exhibit one or two ligand field bands atca. 20000 and 29000 cm^–1 due to the¹ A _1g ¹ T _1g and¹ A _1g ¹ T _2g transitions respectively. Conductance measurements indicate the triunivalent nature of [Co(tropolone)(trien)]I₃, [Co(picolylamine)(trien)]I₃, [Co(3-aminopyridine)(trien)]I₃, [Co(2,2-dipyridyl)(trien)]Cl₃, [Co(biguanide)(trien)]I₃, [Co(propylenediamine)(trien)]I₃ and biunivalent nature of [Co(picolinate)(trien)]Cl₂, [Co(quinaldinate)(trien)]Cl₂, [Co(acetoacetanilido)(trien)]Cl₂, and [Co(ethylacetoacetato)(trien)]I₂. Equivalent weight determination by the ion-exchange resin (H⁺ form) method gives the values of molecular weights which are consistent with the theory. The complexes are diamagnetic.     

Synthesis and Structure of New Cobalt–Carbonyl Complexes Containing Tellurium Atoms

Co₂(CO)₈ and Te₂O react to form the well known Co₄(CO)₁₀Te₂, Co₄(CO)₁₁Te₂ complexes and the two new cluster complexes CCo₆(CO)₁₂Te₂(1), and CCo₆(CO)₁₀Te₂(Te₃) (2). The structures of 1 and 2 were determined by X-ray analysis, together with the triphenylphosphine derivative of 1, CCo₆(CO)₁₁(PPh₃)Te₂(3), which was analyzed to clarify the disordered structure of the parent compound. Complex 1 is formed by a prismatic cluster of cobalt atoms with a carbon embedded in the cage; two tellurium atoms cap the triangular faces of the prism and each cobalt atom links two terminal carbonyl groups. The complex 2 has a similar prismatic cage CCo₆; two ₄-Te atoms cap two rectangular faces of the prism, while other two Te atoms bridge two edges of the triangular faces and are linked each other through a third Te atom. Electron counting gives for complex 2 92 electrons: the presence of two long Co–Co distances suggests that the two excess electrons are located on Co–Co antibonding orbitals. Crystal data for 1, space group C2/c, a = 12.845(2) Å, b = 13.449(2) Å, c = 13.246(2) Å, = 91.95(2)°, Z = 4, R = 0.097 for 2555 reflections; for 2, space group Pnna, a = 17.219(5) Å, b= 14.969(6) Å, c = 9.178(4) Å, Z = 4,R = 0.037 for 3103 reflections; for 3, space group P2₁/c, a = 9.288(2) Å, b = 14.920(6) Å, c = 26.300(9) Å, = 99.99(2)°, Z = 4, R = 0.037 for 4300 reflections. The vibrational analysis of the complex 1 was performed and most of the (CO), (₆C–Co), (Co–Co) and (Co–Co) modes were assigned. The (Co–Te) modes were interpreted on the basis of the intermolecular coupling, due to the close contact between neighboring clusters in one distinct direction in the crystal.     

In Situ Investigation of Methane Dry Reforming on Metal/Ceria(111) Surfaces: Metal–Support Interactions and C−H Bond Activation at Low Temperature

Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO₂) surfaces indicate that metal–oxide interactions can play a very important role for the activation of methane and its reforming with CO₂ at relatively low temperatures (600–700 K). Among the systems examined, Co/CeO₂(111) exhibits the best performance and Cu/CeO₂(111) has negligible activity. Experiments using ambient pressure X‐ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO₂(111) at temperatures as low as 300 K—generating CH_x and CO_x species on the catalyst surface. The results of density functional calculations show a reduction in the methane activation barrier from 1.07 eV on Co(0001) to 0.87 eV on Co²⁺/CeO₂(111), and to only 0.05 eV on Co⁰/CeO_2−x (111). At 700 K, under methane dry reforming conditions, CO₂ dissociates on the oxide surface and a catalytic cycle is established without coke deposition. A significant part of the CH_x formed on the Co⁰/CeO_2−x (111) catalyst recombines to yield ethane or ethylene.     

Thermodynamic stability of the γ-Co1−x Se phase by CaF2 electrolyte galvanic cell method

The partial molar free enthalpy of cobalt, , and the molar free enthalpy of formation of Co _x Se alloy phase, G _f ⁰ (Co _x Se) at 873K, were determined by the solid CaF₂ electrolyte galvanic cell method forx=0.725 to 0.956. was observed to be a monotonic function of the mole fractionX _Co in the composition region of the investigation with an inflexion point atX _Co=0.455. The measurements were extended down to a temperature of 710 K and a partial Co–Se phase diagram was evaluated from the resultant data.

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Untersuchung der thermodynamischen Stabilität der -Co-_1–x Se Phase mittels galvanischer Zelle mit CaF₂ Elektrolyt

Zusammenfassung Die partiellen molaren freien Enthalpien von Kobalt ( ) und die molaren freien Bildungsenthalpien der Co _x Se Legierungsphase [G f/0 (Co _x Se) bei 873 K] wurden mittels galvanischer Zelle (CaF₂ Fest-Elektrolyt) fürx=0,725–0,956 bestimmt. wurde im untersuchten Bereich als monotone Funktion vom MolenbruchX _Co, mit einer Inflexion beiX=0,455, gefunden. Die Messungen wurden bis zu einer Temperatur von 710 K ausgedehnt und die Daten wurden zur Erstellung eines partiellen Co–Se-Phasendiagramms ausgewertet.

     

Complexes of some bivalent cobalt,nickel, copper,zinc, cadmium and monovalent silver salts with 4,4′-BipyridylN,N′-dioxide

Summary Coordination compounds have been prepared from 4,4-hipyridylN,N-dioxide (4,4-BipyO₂) and some hivalent metal halides, nitrates and thiocyanates as well as silver(1) nitrate.viz., Co(4.4-BipyO₂)₂Cl₂, Co(4.4-BipyO₂)Br₂, Co(4,4-Bi-pyO₂)(NO₃)₂. Co(4,4-BipyO₂)₂(NCS)₂. Ni(4.4-BipyO₂)₂Cl₂. Ni(4,4-BipyO₂)(NO₃)₂, Ni₂(4.4-BipyO₂)₃(NSC)₄. Cu(4,4-BipyO₂)(NO₃)₂. Zn(4,4-BipyO₂(NO₃)₂, Zn,(4.4-BipyO₂)₃-(NCS)₄. Cd(4.4-BipyO₂)(NO₃)₂, Cd(4.4-BipyO₂)₂(NCS)₂ and Ag(4,4-BipyO₂)(NO₃). The products were characterized by magnetic susceptibility. electronic and i.r. spectral measurements down to 200 cm^–1. Tentative stereochemistries for the complexes isolated in the solid state are proposed. The ligand field parameters 111 Dy. B. j3. )., and calculated for the cobalt. nickel and copper complexes are consistent with these stereochemistries.     

Catalytic Steam Reforming of Methane: New Data on the Contribution of Homogeneous Radical Reactions in the Gas Phase: II. A Ruthenium Catalyst

The kinetics of methane steam reforming and pyrolysis on Ru/Al₂O₃(T= 650–750°C, = 0.001–0.030 MPa) is studied. The values of the rates and activation energies are compared with the kinetic parameters for nickel catalysts. It was shown that steam reforming can occur on the ruthenium catalyst both heterogeneously and heterogeneously–homogeneously depending on the reaction conditions. Comparative activities of the Ru/Al₂O₃and Ni–Al₂O₃catalysts are discussed under the conditions of purely heterogeneous and heterogeneous–homogeneous steam reforming.     

Synthesis of 4-Dicyclohexylaminomethyl Antipyrine and Its Metal Complexes: Spectral Characterization and Evaluation of Thermodynamic Parameters

Complexes of Fe(III), Co(II), Ni(II), and Cu(II) with 4-dicyclohexylaminomethyl antipyrine (DCHAMA, L) were prepared and characterized by elemental and chemical analyses, IR, electronic absorption, ¹H NMR and EPR spectroscopies, thermal analysis, and magnetic susceptibility measurements. The stoichiometry of the complexes was found to be MLX₂, MLX₃, or MLX₂(H₂O)₂ where X = Cl or NO₃. The ligand exhibits a bidentate mode of coordination. Thermal analysis of the chloro complexes shows a three stage decomposition pattern for the Cu(II) complex and a two stage decomposition pattern for Fe(III) and Co(II) complexes to yield the respective metal oxides as the end product. Kinetic and thermodynamic parameters such as n, E _a, H ^#, S ^#, and G ^# were calculated using Coats–Redfern and Madhusudhanan–Krishnan–Ninan integral methods. The coordination number of the metal atom is found to influence the thermal stability of the complexes. The antimicrobial screening shows that the four-coordinated complexes are more active than the five- and six-coordinated ones and DCHAMA.     

Electron transfer: 150. The reaction of corrin-bound cobalt(III) with indium(I) — an additional mechanistic variation

(Corrin)cobalt(III) is reduced by indium(I) to its Co(II) counterpart (cob(II)alamin, B_12r) at pH 1-2 in aqueous chloride. In these solutions the aqua oxidant (B_12a) is in mobile anation equilibrium with its chloro derivative. At [Cl^–] 0.03 M, consumption of Co(III) is exponential and proceeds by parallel paths involving the aqua- and chloro-substituted oxidants. At [Cl^–] 0.10 M, rates are governed mainly by an preliminary act requiring In(I) and 2 Cl^–, but no Co(III). This initiation step generates a more reactive In(I) species which is taken to result from a slow heterolysis and loss of ligating water from InCl₂ ^–(aq).     

The reaction of alkoxides with dicobalt octacarbonyl: Trapping of the Co(I) intermediate in the disproportionation (“base reaction”) with a hardLewis base

Dicobalt octacarbonyl reacts with alcoholates (RO^–) yielding alkoxycarbonylcobalt tetracarbonyls,ROC(O)Co(CO)₄.

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Reaktion von Alkoxiden mit Dicobaltoctacarbonyl: Abfangen des Co(I) Zwischenproduktes in der Disproportionierung (Basen-Reaktion) mit einer hartenLewis Base (Kurze Mitteilung)

Zusammenfassung Dicobaltoctacarbonyl reagiert mit Alkoxiden (RO^–) zu Alkoxycarbonylcobalt tetracarbonylen,ROC(O)Co(CO)₄.

     

Thermal Behaviour of Metal Complexes of 6-(2-Pyridylazo)-3-acetamidophenol

The present work aims chiefly to study the thermal behaviour of complex compounds with general formula: [M(HL)xH₂O](A)yH₂O (where HL=C₁₃H₁₁N₄O₂=6-(2-pyridylazo)-3-acetamidophenol (PAAP), M=Cu(II), Zn(II), Cd(II) and Fe(III) x=1, 3; y=2, 5) while A=CH₃COO^– (Ac), Cl₂. The second formula is [M(H₂L)xH₂O]Cl₂yH₂O, (where H ₂ L=C₁₃H₁₂N₄O₂ (PAAP), M=Ni(II), Co(II) x=3; y=4, 6). The compounds were identified by elemental analysis, FT-IR spectra and TG/DTG,DTA methods. It was found that during the thermal decomposition of complex compounds water molecules of crystallization are released in the first step. In the next step the pyrolysis of organic ligand takes place. Metal oxide remained as a solid product of the thermal decomposition. Mass spectroscopy has been used for the determination of the thermal decomposition on the intermediate products. It was found that the thermal stability of the studied compounds increases as the ionic radii decreases. The activation energy E, the entropy change S ^*, the enthalpy H ^* change and Gibbs free energy change G ^* were calculated from TG curve.This revised version was published online in November 2005 with corrections to the Cover Date.     

Catalytic properties of chromites with a spinel structure in the oxidation of CO and hydrocarbons and reduction of nitrogen oxides

The catalytic activity of supported chromites MCr₂O₄/-Al₂O₃ (M = Cu, Co, Mn, Zn, Mg) in the oxidation of CO, C₃H₆, and o-xylene and NO_x reduction was studied. The catalytic activity depends on the calcination temperature and cation nature. The features of the formation of the catalysts were studied by the UV-Vis diffuse reflectance and IR spectroscopies.     

Absorption spectra and bond type in Co(II) aquoamino complexes

Absorption spectra are reported for solutions containing Co(II) and ammonia. Spectra are calculated for five Co(II) aquoamino complexes. The spectra are used to determine Dq and B, parameters of the bonds in these compounds. It is found that Dq and B change nonlinearly and nonadditively. The parameters _c, Dt, Ds, and have also been established for [Co(H₂O)₆]²⁺ and [Co(NH₃)₆]²⁺. The parameter variation can be explained if the H₂O molecules form weaker bonds to the central atom than do the NH₃ molecules, but are capable of d-p interaction.     

Coordination compounds of N-(2-aminophenyl)- and N-(3-aminophenyl)pyridine-2′-carboxamide with cobalt(II) and cobalt(III). The nature of amide deprotonation induced by cobalt(III) in acidicpH

New complexes of the general formulae CoL ₂ X·nH₂O (X=Cl, Br, I, NCS, NO₃ andn=0, 1, 2 or 3), Co₂ L ₂ X ₃·EtOH (X=Cl, Br, I, NCS), Co(DH)X ₂ (X=NCS, NO₃) and Co(DH)₂ X ₂ (X=NCS, I) have been prepared, whereLH=N-(2-aminophenyl)pyridine-2-carboxamide andDH=N-(3-aminophenyl)pyridine-2-carboxamide. The compounds were characterized by X-ray powder patterns, conductivity measurements, thermogravimetric analysis, magnetic properties as well as by IR, ligand field and¹H-NMR spectroscopy. In the presence of oxygen,LH undergoes a cobalt(III) ion promoted amide hydrogen ionization in thepH region 4–6.

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Koordinationsverbindungen von N-(2-aminophenyl)- und N-(3-aminophenyl)pyridin-2-carboxamid mit Cobalt(II) und Cobalt(III). Die Natur der Deprotonierung von Amiden induziert von Cobalt(III) in saurem Medium

Zusammenfassung Neue Komplexe der allgemeinen Formeln CoL ₂ X·nH₂O (X=Cl, Br, I, NCS, NO₃ undn=0, 1, 2, 3), Co₂ L ₂ X ₃·EtOH (X=Cl, Br, I, NCS), Co(DH)X ₂ (X=NCS, NO₃) und Co(DH)₂ X ₂ (X=NCS, I) wurden dargestellt mit LH=N-(2-aminophenyl)pyridin-2-carboxamid undDH=N-(3-aminophenyl)pyridin-2-carboxamid. Die Verbindungen wurden mittels Röntgenstrukturanalyse, Leitfähigkeitsmessungen, thermogravimetrischen Analysen, magnetischen Eigenschaften sowie mit IR-, Ligandenfeld- und¹H-NMR-Spektroskopie charakterisiert. In Gegenwart von Sauerstoff unterliegtLH einer Cobalt(III)ion-induzierten Amidwasserstoffionisierung impH-Bereich 4–6.

     

Secondary ion emission of selected transition metals under nitrogen oxides

The emission of various positive secondary ions has been investigated for polycrystalline targets of Ti, V, Cr, Nb, Ta, Co, Ni, Cu, Pd and Pt, which were bombarded by Ar⁺ ions under dynamic SIMS (DSIMS) conditions in the presence of the gaseous nitrogen oxides N₂O, NO and NO₂ at fixed pressure and under residual gas. Besides ions of the Me⁺ type several fragmentary ions (e.g. N⁺, O⁺, NO⁺, MeN⁺ and MeO⁺) and also cluster ions Me _x O _y ⁺ (x 2, 0 y 2) were detected. Signals of a more molecular type with respect to the reactant gas, e.g. MeNO⁺, were only found for Co, Ni, Cu, Pd and Pt. From this, one may infer that for the other targets the nitrogen oxides will exist preferentially in a dissociatively adsorbed state at the metal surface. Several aspects of secondary ion emission can be explained assuming a different degree of oxidation for the metals under the influence of reactant gas.Part of the dissertation     

Physicochemical properties of electrode materials based on substituted yttrium manganite

Electrode materials Y_0.5Ca_0.5Mn_1–x (Co,Ni)_xO₃(x = 0–0.1) have an o-orthorhombic perovskite structure. Doping with transition metals raises the content of ions Mn⁴⁺ from 49% at x = 0 to 62% at x = 0.05 Ni. At 500–650 K there takes place an o-o-orthorhombic transition, with the thermal expansion coefficient rising from (7.1–8.1) × 10^–6 to (10.5–11) × 10^–6 K^–1. Composition Y_0.5Ca_0.5Mn_1–x (Co, Ni)_xO₃ is n-type semiconductor with a considerable oxygen constituent at >1000 K. Effect of the electrode material composition on the resistance parameter (/d) of an intermediate layer E/SE and on the polarization resistance (R ) of the triple-phase boundary E/SE/GP is similar. At 300–1100 K and 10²–10⁵ Pa, minimum values of these quantities are exhibited by samples with the Y_0.5Ca_0.5Mn_0.95Ni_0.05O₃ electrode layer 50 mg cm^–2 thick.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 291–297.Original Russian Text Copyright © 2005 by Tikhonova, Poluyan, Glushko, Vecher, Znosok.     

Electrosynthesis and magnetic behaviour of neutral cobalt(II) complexes of pyridine-2-carbaldehyde pyridin-2′-ylhydrazone (papyH) and its analogues

Summary Neutral cobalt(II) complexes with the tridentateN-heterocyclic ligand pyridine-2-carbaldehyde pyridin-2-ylhydrazone (papyH) and its analogues have been prepared by the electrochemical oxidation of cobalt in an acetone solution of the hydrazone. The [Co(papy)₂] complexes are obtained as red-green dichroic microcrystals due to the extended-conjugation system in the anionic ligand. The magnetic moments of the octahedral cobalt(II) chelates decrease continuously from _eff = 1.81–4.63 B.M. at room temperature to 1.7–4.08 B.M. atca. 90K. The changes in magnetic moment have been accounted for by a⁴ T ₁² E spin crossover system.     

Synthesis, Structure and Spectroscopy of Clathrate Inclusion Compounds of Cobalt(II), Cadmium(II) and Zinc(II) trans-4-styrylpyridine nitrates as Host with trans-4-styrylpyridine as Guest (2 : 1)

New clathrate inclusion compounds with the general formula,MA₃X₂ 1/2G (M = Co(II)(1),Cd(II)(2), and Zn(II)(3), X = NO₃ ^- andA and G = trans-4-styrylpyridine), differing from the usualWerner clathrates, MA₄X₂ 2G, have been prepared and characterized by elemental and thermal analyses,IR and electronic spectroscopy and X-ray crystallography. Tworepresentative compounds [Co(stpy)₃(NO₃)₂] 1/2stpy (1) and [Cd(stpy)₃(NO₃)₂] 1/2 stpy (2)are investigated by single crystal X-ray diffraction. Compound (1)crystallizes in the triclinic space group P¯1 with a = 10.966(2),b = 12.802(4), c = 16.063(5) Å = 83.38(3), = 71.30(2), = 76.88(3) °,Z = 2. The structure is made up of discretemolecules of [Co(stpy)₃(NO₃)₂]. The central Co(II) issurrounded by three stpy nitrogen atoms and four oxygen atoms of twoasymmetrically coordinated bidentate nitrate ligands. One of the oxygensis semicoordinated leading to a distorted octahedral geometry for Co(II).Compound (2) crystallizes in the monoclinic space group P2₁/nwith a = 15.597(3), b = 18.313(5), c = 16.188(3) Å = 115.998(14)° and Z = 4. The structure consists of neutralmolecules of [Cd(stpy)₃(NO₃)₂]. The geometry aroundCd(II) is best described as pentagonal bipyramid with four oxygen atomsfrom symmetrical bidentate nitrate groups and one stpy nitrogen atom inthe equatorial positions. Two other nitrogen atoms from stpy ligands occupythe axial positions. The guest stpy molecules are trapped in the centrosymmetricalcavities in lattices of both 1 and 2. Compound 3is found to beisomorphous with 2. A large splitting of the symmetric and asymmetricNO₂ stretching vibrations reveals the presence of bidentate nitrate ligands.Thermogravimetric and DTA studies on the Cd(II) compound, show it to be athermally stable inclusion compound.     

Application of cross-correlation analysis to EXAFS: Investigation of the cobalt phase on boron modified cobalt/alumina catalysts

Boron modified Co/Al₂O₃ catalysts, previously characterized by ESCA, are examined by EXAFS. A method of data analysis based on cross-correlation of the (E) spectra is used to determine the relative amounts of Co₃O₄ and cobalt surface phase present on the catalysts. The results are compared with those obtained previously by ESCA. The EXAFS analysis agrees well with the ESCA results. No gas-phase reactions were required to elucidate the relative proportion of cobalt species by EXAFS as is necessary for the ESCA analysis.