Characterization of CoMn catalyst by in situ X-ray absorption spectroscopy and wavelet analysis for Fischer–Tropsch to olefins reaction

Cobalt carbide has recently been reported to catalyse the FTO conversion of syngas with high selectivity for the production of lower olefins(C_2–C_4). Clarifying the formation process and atomic structure of cobalt carbide will help understand the catalytic mechanism of FTO. Herein, hydrogenation of carbon monoxide was investigated for cobalt carbide synthesized from CoMn catalyst, followed by X-ray diffraction, transmission electron microscopy, temperature programmed reaction and in situ X-ray absorption spectroscopy. By monitoring the evolution of cobalt carbide during syngas conversion, the wavelet transform results give evidence for the formation of the cobalt carbide and clearly demonstrate that the active site of catalysis was cobalt carbide.     

Characterization of TcCl4 and β-TcCl3 by X-ray absorption fine structure spectroscopy

Technetium tetrachloride and β-TcCl₃, synthesized from the reaction of Tc metal and Cl_2(g) in sealed tubes, were characterized by X-ray absorption fine structure spectroscopy. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements are in good agreement with the X-ray diffraction structures of the two compounds. For TcCl₄, the absorbing Tc atom is surrounded by Cl atoms at 2.34(2) Å and Tc atoms at 3.66(4) Å. For β-TcCl₃, the absorbing Tc atom is surrounded by Cl atoms at 2.40(2) Å and Tc atoms at 2.81(3), 3.66(4) and 5.71(6) Å. EXAFS spectroscopy indicates that the TcCl₄ and β-TcCl₃ samples obtained by sealed tube reactions are single phase. The X-ray absorption near edge structure spectra of TcCl₄ and β-TcCl₃ were recorded; the positions of the Tc K-edges of β-TcCl₃ (21,050.5 eV) and TcCl₄ (21,053.0 eV) are compared to the ones measured for α-TcCl₃ (21,051.0 eV) and TcCl₂ (21,048.8 eV). A correlation between the positions of the Tc K-edges and the oxidation state of the Tc atom in technetium binary chlorides was determined.     

Effect of thickness and monolayer location on thermostability of metal stearate LB films studied by FT-IR reflection—absorption spectroscopy

LB films of Cd and Ca stearates with 1, 3, 9, and 21 monolayers were fabricated on silver-coated glass slides. 9-Monolayer LB films of Cd and Ca salts of deuterated stearic acid, in which the 1st, 5th, or 9th layer was replaced by 1 monolayer of undeuterated analogues, were also prepared on the above substrates. Temperature dependences of Fourier transform infrared (FT-IR) reflection—absorption (RA) spectra were examined for these LB films in the range 31–140°C. At room temperature, the hydrocarbon chains in these LB films were in a well-ordered state with a high degree of perpendicular orientation to the substrate. However, they became disordered at elevated temperatures. These order-disorder phase transition temperatures were dependent on the film thickness, to a small degree in the Cd stearate LB film (102–108°C), but to a large degree in the Ca stearate LB film (103–129°C). In the latter LB film, the effect of dehydration was inferred. The degree of disorder at high temperatures was dependent on the film thickness and the location of monolayer in the 9-monolayer LB films. This result is discussed in terms of the internal pressure within the LB film.     

In situ phosphorus K-edge X-ray absorption spectroscopy studies of calcium–phosphate formation and transformation on the surface of bacterial cellulose nanofibers

In this work, for the first time, in situ formation and transformation process of embryo calcium phosphate (Ca–P) minerals on three-dimensional bacterial cellulose nanofibers was investigated. Combined with XRD, X-ray absorption near-edge structure results revealed that the embryo precursor was amorphous calcium phosphate which was subsequently converted to β-tricalcium phosphate, octacalcium phosphate, and finally to the more thermodynamically stable form of hydroxyapatite. The methodology reported herein may be extended to the studies of Ca–P and other minerals on various substrates.     

Vibrational spectroscopy at high pressures—LVI. A Raman study of some alkali metal halates,and the X-ray compressibility of KClO3

Raman spectra at high pressure have been obtained for KBrO₃, NaClO₃ and NaBrO₃ in a diamond anvil cell. A phase change has been found for KBrO₃ at 19 kbar; at 24 kbar for NaBrO₃; and at 36 kbar for NaClO₃. The bulk compressibility of KClO₃ has been determined by X-ray diffraction using synchrotron radiation and found to be 2.36 × 10⁻² GPa⁻¹, in good agreement with Bridgman's value.     

X-ray absorption spectroscopy to analyze nuclear geometry and electronic structure of biological metal centers—potential and questions examined with special focus on the tetra-nuclear manganese complex of oxygenic photosynthesis

X-ray absorption spectroscopy (XAS) has become a prominent tool for the element-specific analysis of transition metals at the catalytic center of metalloenzymes. In the present study the information content of X-ray spectra with respect to the nuclear geometry and, in particular, to the electronic structure of the protein-bound metal ions is explored using the manganese complex of photosystem II (PSIII) as a model system. The EXAFS range carries direct information on the number and distances of ligands as well as on the chemical type of the ligand donor function. For first-sphere ligands and second-sphere metals (in multinuclear complexes), the determination of precise distances is mostly straightforward, whereas the determination of coordination numbers clearly requires more effort. The EXAFS section starts with an exemplifying discussion of a PSII spectrum data set with focus on the coordination number problem. Subsequently, the method of linear dichroism EXAFS spectroscopy is introduced and it is shown how the EXAFS data leads to an atomic resolution model for the tetra-manganese complex of PSII. In the XANES section the following aspects are considered: (1) Alternative approaches are evaluated for determination of the metal-oxidation state by comparison with a series of model compounds. (2) The interpretation of XANES spectra in terms of molecular orbitals (MOs) is approached by comparative multiple-scattering calculations and MO calculations. (3) The underlying reasons for the oxidation-state dependence of the XANES spectra are explored. Furthermore, the potential of modern XANES theory is demonstrated by presenting first simulations of the dichroism in the XANES spectra of the PSII manganese complex.     

Chiral ferrocenes derived from (+)-longifolene—determination of the configuration by NMR spectroscopy and X-ray crystallography

The addition of monolithium ferrocene to exo-longifolyl aldehyde and endo-longifolyl aldehyde, respectively, prepared from (+)-longifolene, leads to four diastereoisomeric α-hydroxyalkyl ferrocenes, which were isolated in pure form. The configurations of the newly formed stereogenic centers were determined by means of NMR spectroscopy and X-ray crystallography.     

Silver electrodeposition from water–acetonitrile mixed solvents. Part III—an in situ investigation by optical second harmonic generation spectroscopy

In this work, we report an investigation based on silver electrodeposition from water–acetonitrile mixed solvents onto a polycrystalline Au electrode, based on in situ optical second harmonic generation (SHG) spectroscopy. This paper is the last one of a series attacking the same topic by cyclic voltammetry and potentiostatic current transients (Mele et al., J Solid State Electrochem in press, 1) and in situ surface-enhanced Raman scattering (Mele et al., J Solid State Electrochem in press, 2). SHG intensity transients following the application of potentiostatic cathodic steps have been measured in order to obtain detailed information on the formation of Ag clusters and nuclei during the electrodeposition process. Our SHG data have been rationalised in terms of a simple optical model accounting for SHG enhancement brought about by Ag cluster formation.     

Study of N,N′-dihydroxyethyldithiooxamide by X-ray diffraction,u.v.-vis,NMR, Raman and i.r. spectroscopy

The vibrational, NMR and electronic spectra of HO(CH₂)_xNHCSCSNH(CH₂)_xOH (x = 2,3,5,6) are discussed. A vibrational analysis has been proposed for the N,N′-dihydroxyethyldithiooxamide (x = 2) and its deuterated (NH/ND, OH/OD) analogue. The structure of N,N′-DHEDTO was solved by X-ray analysis. M_r = 208, monoclinic, space group P2₁/n, a = 9.8800(5) Å, b = 11.3260(7) Å, c = 9.7806(8) Å, β = 119.366(5)°, V = 953.8 ų, Z = 4, Dc = 1.365 Mgm⁻¹,μ(CuKα) = 0.47 mm⁻¹, F(000) = 440.00, T = 300 K. Final conventional R-factor = 0.036, R_w = 0.037, for 1608 unique reflections with I > 3.σ(I) out of 1800 measurements. The structure was solved using the automatic programs PATSYS and DIRDIF. The two νOH bands in the i.r. spectrum are in agreement with the crystallographic structure, which proposes that the unit cell of the compound consists of two independent molecules.     

The impact of indium metal as a minor bimetal on the anodic dissolution and passivation performance of zinc for alkaline batteries. Part II: galvanostatic,impedance spectroscopy,and charge–discharge evaluations

Journal of Solid State Electrochemistry - The anodic dissolution and passivation processes of zinc and zinc-indium alloys were investigated in an alkaline solution of 6 M KOH using...     

Transformations of cyclohexa-1,4-diene under the action of biphenyl—alkali metal systems in THF. Synergistic acceleration by mixtures of lithium and sodium

In the interaction of cyclohexa-1,4-diene (1,4-CHD) with a mixture of biphenyl and metallic lithium or sodium in THF at 20 °C, three processes occur, viz., disproportionation of 1,4-CHD to form benzene and cyclohexene, dehydrogenation of 1,4-CHD to form benzene and molecular hydrogen, and dehydrogenation of 1,4-CHD to form benzene and lithium or sodium hydride. In the case of lithium on the use of an equimolar amount of biphenyl, the isomerization of 1,4-CHD to cyclohexa-1,3-diene is also observed. When the molar ratio Li(Na): Ph₂ increases from 1 : 1 to 2 : 1, i.e., when the reaction is carried out in the presence of an alkali metal solid phase, the overall conversion of 1,4-CHD into benzene and cyclohexene increases. The use of mixtures of lithium and sodium leads to acceleration of the processes of the formation of benzene and cyclohexene. The possible mechanism of the synergistic effect found is discussed.     

6,6′-Dimethyl-1,1′,5,5′-tetraaza-6,6′-bi(bicyclo[3.1.0]hexane): synthesis and investigation of molecular structure by quantum-chemical calculations,NMR spectroscopy and X-ray diffraction analysis

Structural Chemistry - A new diaziridine derivative with two bicyclic diaziridine-containing moieties in one molecule,...     

A macrocyclic ligand incorporating both a 2,2′-bipyridyl and a 2,9-diphenyl 1,10-phenanthroline fragment: Reciprocal control of one site by complexation of the other site to a transition metal.

A coordinating system containing two different complexing sites has been synthesised. Binding of ruthenium(II) to the octahedral-preferred part allows complexation of copper(I) at the tetrahedral site.     

Electronic structure of lanthanum transition-metal oxyarsenides LaMAsO (M = Fe,Co, Ni) and LaFe1−xM′xAsO (M′ = Co,Ni) by X-ray photoelectron and absorption spectroscopy

The electronic structures of the quaternary oxyarsenides LaMAsO (M = Fe, Co, Ni) were examined with X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). Interpretation of the metal 2p_3/2 and arsenic 3d_5/2 binding energies, as well as a satellite feature in the Co 2p XPS spectrum, suggests charges that are much less extreme than expected (i.e., not M²⁺ and As^3?) because of the strong covalent character within the M–As bonds. As M is varied, the differing degrees of charge transfer from M to As atoms within these bonds are manifested by shifts in the As 3d_5/2 binding energies and changes in the As K-edge intensities. This charge transfer is isolated within the [MAs] layer and does not influence the O 1s and La 3d XPS spectra. Fitting the experimental valence band spectra of these oxyarsenides LaMAsO yielded electron populations of states that support the formal charge assignment [La³⁺O^2?][M²⁺As^3?]. The mixed-metal series LaFe_1?xM′_xAsO (M′ = Co, Ni) was examined by XANES; analysis of the metal K- and L-edges, as well as of the Co 2p XPS satellite feature, revealed that no metal–metal charge transfer takes place.     

Amplification of chirality by transition metal coordination: synthesis of chiral allenes and allene manganese complexes of high enantiomeric purity. Synthesis of methyl (R,E)-(−)-(2,4,5-tetradecatrienoate (pheromone of Acanthoscelides obtectus (say))

The enhancement of the asymmetry of chiral allenes by coordination with a transition metal can be turned to account for (easy) resolution of the complexes and therefore the allenes themselves. This is illustrated here on allene aldehyde complexes of (η-methylcyclopentadienyl) dicarbonylmanganese, possibly bearing a second electron withdrawing substituent, and by the synthesis of an optically active alkenylallenic insect pheromone of high enantiomeric purity.     

Enhanced lithium electrochemical performance and optical properties of CeO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript> nanocomposite thin films by transition metal (TM: Ni,Mn, and Co) doping

Undoped and transition metal (TM: Ni, Mn, Co)-doped CeO₂–SnO₂ nanocomposite thin films were prepared by sol-gel dip coating (SGDC) technique. The grazing incidence X-ray diffraction (GIXRD) patterns indicated that CeO₂–SnO₂ film has a cubic structure of CeO₂ and the crystallinity deteriorated with incorporation of dopant. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed that the surface morphology of the films was affected by TM incorporation. The surface roughness and fractal dimensions of CeO₂–SnO₂ films increased with doping. The average transmittance of CeO₂–SnO₂ thin film is found nearly 80% in the visible region and increased with doping. The absorption edge revealed a blue shift toward shorter wavelengths after incorporation of TM ions. The compositional dependence of optical parameters such as refractive index, extinction coefficient, and optical conductivity were also investigated. Cyclic voltammetry measurements showed that ion storage capacity was decreased significantly with increasing scan rate. The undoped and doped CeO₂–SnO₂ films showed good reversible cycle of intercalation/deintercalation of Li⁺ ions. The ion storage capacity and electrochemical stability were enhanced with transition metal doping. The Mn-doped CeO₂–SnO₂ composite thin film had better ion storage capacity rather than other samples due to its special porous morphology. The Li diffusion toward electrode surface was described in terms of self-similar fractal dimension. A quenching in blue-green photoluminescence (PL) intensity of CeO₂–SnO₂ films was occurred by transition metal doping.

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Hydrothermal syntheses and crystal structures of two transition metal complexes supported by vanadate {V4O12}: {[ M (dpa)2]2V4O12} ( M = Co,Ni. dpa = 2,2′-dipyridylamine)

Hydrothermal reactions have been exploited in the syntheses of two new metavanadates, {[Co(dpa)₂]₂V₄O₁₂}?·?H₂O (1) and {[Ni(dpa)₂]₂V₄O₁₂}?·?H₂O (2), which were characterized by X-ray diffraction, IR and thermogravimetric analysis. Crystal data: C₄₀H₃₈N₁₂O₁₃Co₂V₄ (1) monoclinic. P2(1), a?=?10.126(2), b?=?17.639(4), c?=?12.930(3) Å,?α?= 90°,?β?= 98.356(4)°,?γ?= 90°, Z?=?2; C₄₀H₃₈N₁₂O₁₃Ni₂V₄ (2) monoclinic. P2(1), a?=?10.1037(9), b?=?17.6680(14), c?=?12.8832(10) Å,?α?= 90°,?β?= 98.423(2)°,?γ?= 90°, Z?=?2. The two complexes are isomorphic and their structures consist of a [V₄O₁₂]^4? cluster bound to two [M(dpa)₂]²⁺ moieties through the terminal oxygen atoms in a trans-conformation; the [V₄O₁₂]^4? cluster adopts a chair-like configuration.     

Homogeneous catalysis by transition metal complexes. Part VI: Hydroformylation of 1-octene catalysed by [η5-C5R5M(CO)2X] and [η5-C5R5M(CO)2]2 species (R = H,CH3, C6H5; M = Fe,Ru; X = Cl,Br, I)

The hydroformylation of 1-octene catalysed by the title compounds has been examined at 135 °C under an atmosphere of H₂ and CO at a pressure of 85 atm. The influence on the activity and selectivity of various parameters such as the nature of the metal, the nuclearity of the original complex and the electronic and steric effects induced by the substituents on the cyclopentadienyl ligand has been investigated and discussed.