Thermal analysis and epr studies of carbon black oxidation in the presence of copper loaded Y2O3-CeO2-ZrO2 catalyst

The activity of copper-free and copper-loaded 10Y₂O₃-10CeO₂-80ZrO₂ solid solutions towards carbon black combustion was studied using simultaneous thermogravimetric analysis and differential thermal analysis techniques coupled with gas chromatography. It was demonstrated that all studied catalysts lower the temperature of carbon black combustion. The selectivity of the catalytic reaction in CO₂ formation was 100%. The comparison of electron paramagnetic resonance (EPR) spectra of pure catalysts with those of the samples (catalysts mixed with carbon black) after catalysis allowed to evidence, despite of the strong oxidizing atmosphere, a thermal reduction by carbon of Fe³⁺ (impurities), Cu²⁺ and Zr⁴⁺ during the reaction. Moreover a new EPR signal appeared after catalytic test and was attributed to the presence of paramagnetic metal-carbon or/and metal-sulphur complexes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Potential of Supported Copper and Potassium Oxide Catalysts in the Combustion of Carbonaceous Particles

Different oxide carriers (TiO₂ and ZrO₂) as supports for low amounts of Cu²⁺ and K⁺ species (2 wt % as equivalent oxide) were tested in the catalytic oxidation of carbon black. The K-Cu/oxide catalysts were shown to have a lower soot combustion temperature than K/oxide, Cu/oxide, and pure oxide carriers. The K-Cu/ZrO₂ catalyst was found to be the most active; it exhibited activity in a loose contact nearly similar to that obtained in a tight contact mode. Physicochemical characterization by EPR, XPS, and TPR revealed the interaction of K⁺ species with Cu²⁺ species and the ZrO₂ carrier in K-Cu/ZrO₂ as well as a strongly distorted Cu²⁺ species on the ZrO₂ surface. The potassium ions ensure promoting effects towards the contact between the carbon black and the catalyst surface. Although potassium ions were found to lower the reducibility of the cupric oxide species, the oxidation rate of carbon black increased in the presence of K/oxide and K-Cu/oxide.     

Chemisorption of copper(II) at zinc and cadmium dialkyldithiocarbamates: EPR and X-ray diffraction studies

Chemisorption of Cu²⁺ cations at zinc and cadmium dialkyldithiocarbamates was studied. According to EPR data, in the first step, the zinc and cadmium atoms are partially replaced by copper in the starting molecular structure to form heterobinuclear and heteropolynuclear complexes. In the second step, copper replaces up to 90 to 97% of the total number of the metal atoms, yielding binuclear and polynuclear copper(II) complexes. The possibility of the existence of heterobinuclear complexes in the individual state was demonstrated with [CuCd{S₂CN(C₂H₅)₂}₄] as an example. Its molecular and crystal structures were determined from X-ray diffraction data.     

Chemical characteristics of the products of the complexation reaction between copper(II) and a tetra-aza macrocycle in the presence of chloride ions

The reaction of copper(II) perchlorate with the hydrochloride salt of 3,6,9,15-tetra-azabicyclo[9.3.1]penta-deca-1,11,13-triene (L1) in acetonitrile forms two macrocyclic complexes that can be characterized: [L1Cu^IICl][ClO₄] (1) and [L1Cu^IICl]₂[CuCl₄] (2). The structural, electronic, and redox properties of these complexes were studied using spectroscopy (EPR and UV–visible) and electrochemistry. In addition, the solid-state structure of 1 was obtained using X-ray diffraction. The copper(II) is five-coordinate ligated by four N-atoms of the macrocycle and a chloride atom. EPR studies of 1 both in DMF and aqueous solution indicate the presence of a single copper(II) species. In contrast, EPR studies of 2 performed in frozen DMF and in the solid-state reveal the presence of two spectroscopically distinct copper(II) complexes assigned as [L1Cu^IICl]⁺ and [Cu^IICl₄]^2?. Lastly, electrochemical studies demonstrate that both [L1Cu^IICl]⁺ and [Cu^IICl₄]^2? are redox active. Specifically, the [L1Cu^IICl]⁺ undergoes a quasi-reversible Cu(II)/(I) redox reaction in the absence of excess chloride. In the presence of chloride, however, the chemical irreversibility of this couple becomes evident at concentrations of chloride that exceed 50 mM. As a result, the presence of chloride from the chemical equilibrium of this latter species impedes the reversibility of the reduction of [L1Cu^IICl]⁺ to [L1Cu^ICl]⁰.     

Bis -(3,5-dimethyl-pyrazolyl-1-methyl)-(3-phosphanyl-propyl)-amine complexes of copper(II), nickel(II), and cobalt(II)

A series of Cu(II), Co(II), and Ni(II) complexes of bis-(3,5-dimethyl-pyrazolyl-1-methyl)-(3-phosphanyl-propyl)-amine C₁₅H₂₆N₅P (1), prepared from 3-aminopropylphosphine and 1-hydroxymethyl-3,5-dimethylpyrazole were characterized. The nature of bonding and the geometry of the complexes have been deduced from elemental analysis, infrared, electronic, ¹H NMR, ³¹P NMR spectra, magnetic susceptibility, and conductivity measurements. The studies indicate octahedral geometry for nickel complex and square pyramidal geometry for copper and cobalt complexes. The EPR spectra of copper complex in acetonitrile at 300 K and 77 K were recorded. Biological activities of the ligand and metal complexes have been studied on Staphylococcus aureus, Escherichia coli, Aspergillus niger, and Aspergillus flavus by well-diffusion method. The zone of inhibition values were measured at 37°C for a period of 24 h. The electrochemical behavior of copper complexes was studied by cyclic voltammetry. Catalytic study indicates the copper complex has efficient catalytic activity in oxidation of amitriptyline.     

Distribution and properties of catalytically active Cu2+ sites in mesoporous MCM-41 modified with Al, Zr, or W ions

The surface of pure mesoporous SiO₂ with an MCM-41 structure has been modified by introducing Al, Zr, or W ions (1 mmol/g). The original and modified materials have been loaded with Cu²⁺ ions. The distribution, properties, and thermal stability of different Cu²⁺ sites have been studied by EPR and IR spectroscopy. The resulting catalysts have been tested for activity in ethane oxidation. The modification of original MCM-41 exerts a very strong effect on the stability of isolated Cu²⁺ ions on the support surface. Among the modified supports, Al-MCM-41 affords the highest thermal stability and degree of dispersion (70–80%) of the copper-containing phase. There is no correlation between the total number of surface Cu²⁺ sites and the catalytic activity. The specific catalytic activity (per Cu²⁺ ion accessible to the reactants) depends strongly on the local structure of the sites. The isolated pentacoordinated Cu²⁺ sites stabilized by the Al-MCM-41 surface show a comparatively high activity in the sample calcined at 520°C. The heat treatment of Cu/Al-MCM-41 at 650–750°C reduces the specific activity of the catalytic sites by a factor of ～20 without sintering the copper phase, as in the case of CuHZSM-5 zeolite. The least dispersed copper phase, which is observed in the original MCM-41 and likely consists of aggregates of weakly interacting Cu²⁺ ions, exhibits the highest specific activity and thermal stability. In the case of Cu/W-MCM-41, heat treatment causes both the sintering of copper particles and a decrease in the specific activity of the surface Cu²⁺ ions.     

Density functional theory study of the interaction of CP2*ZrCH 3+ (Cp* = C5H5, C5Me5, and C13H9) with ethylene molecule

Density functional theory was used to study gas-phase reactions between the Cp₂*ZrMe⁺ cations, where Cp* = C₅H₅ (1), Me₅Cp = C₅Me₅ (2), and Flu = C₁₃H₉ (3), and the ethylene molecule, Cp₂*ZrMe⁺ + C₂H₄ → Cp₂*ZrPr⁺ → Cp₂*ZrAllyl⁺ + H₂. The reactivity of the Cp₂*ZrMe⁺ cations with respect to the ethylene molecule decreased in the series 1 > 3 ≈ 2. Substitution in the Cp ring decreased the reactivity of the Cp₂*ZrMe⁺ cations toward ethylene, in agreement with the experimental data on the comparative reactivities of complexes 1 and 3. The two main energy barriers along the reaction path (the formation of the C-C bond leading to the primary product Cp₂*ZrPr⁺ and hydride shift leading to the secondary product Cp₂*Zr(H₂)Allyl⁺) vary in opposite directions in the series of the compounds studied. For Flu (3), these barriers are close to each other, and for the other compounds, the formation of the C-C bond requires the overcoming of a higher energy barrier. A comparison of the results obtained with the data on the activity of zirconocene catalysts in real catalytic systems for the polymerization of ethylene led us to conclude that the properties of the catalytic center changed drastically in the passage from the model reaction in the gas phase to real catalytic systems.     

Synthesis,spectral characterization,electrochemistry and catalytic activities of Cu(II) complexes of bifunctional tridentate Schiff bases containing O?N?O donors

Paramagnetic copper(II) complexes of the type [Cu(PPh₃)(L)] (where L = bifunctional tridentate Schiff bases) were synthesized from the reaction of anthranillic acid with salicylaldehyde (H₂L¹), 2‐hydroxy‐1‐naphthaldehyde (H₂L²), o‐hydroxyacetophenone (H₂L³) and o‐vanillin (H₂L⁴) with monomeric metal precursor [CuCl₂(PPh₃)₂]. The obtained complexes were characterized by elemental analysis, magnetic susceptility and spectroscopic methods (FT‐IR, UV–vis and EPR and cyclic voltammetry). EPR and redox potential studies have been carried out to elucidate the electronic structure, nature of metal–ligand bonding and electrochemical features. EPR spectra exhibit a four line pattern with nitrogen super‐hyperfine couplings originating from imine nitrogen atom. These planar complexes possess a significant amount of tetrahedral distortion leading to a pseudo‐square planar geometry, as is evidenced from EPR properties. Cyclic voltammograms of all the complexes display quasireversible oxidations, Cu(III)? Cu(II), in the range 0.31–0.45 V and reduction peaks, Cu(II)? Cu(I),in the range ?0.29 to ?0.36 V, involving a large geometrical change and irreversible. The observed redox potentials vary with respect to the size of the chelate ring of the Schiff base ligands. Further, the catalytic activity of all the complexes has been found to be high towards the oxidation of alcohols into aldehydes and ketones in the presence of N‐methylmorpholine‐N‐oxide as co‐oxidant. The formation of high valent Cu^IV?O oxo species as a catalytic intermediate is proposed for the catalytic process. Copyright © 2008 John Wiley & Sons, Ltd.     

Determination of Trace Copper by Fluorescence Spectrophotometry Based on Cu(DP)2+ and Cu‐4.0‐Generations Polyamidoamine Dendrimers Catalyze Cu2+ to Oxidize Fluorescein

Abstract

Fluorescein can emit strong and stable fluorescence. Cu²⁺ can oxidize fluorescein, which causes the fluorescence signal to diminish. Cu(DP)²⁺ (DP refers to α,α′‐dipyridyl) and Cu‐GPD‐4.0 (GPD‐4.0 refers to 4.0‐generations polyamidoamine dendrimers) both can catalyze Cu²⁺ to oxidize fluorescein, which causes the fluorescence signal to diminish sharply. The ΔF is directly proportional to the content of copper. Based on the facts above, a new catalytic fluorescence spectrophotometry for the determination of trace copper using Cu(DP)²⁺ and Cu‐GPD‐4.0 was established. The linear range of this method is 0.040–28 pg mL^?1. The regression equation for working curve is ΔF=209.5+14.39 C_Cu ²⁺ (pg mL^?1), n=7; correlation coefficient is 0.991. The detection limit of this method is 1.0×10^?14 g mL^?1. After replicate measurement times, RSDs are 3.1% and 4.2% for samples containing 0.040 and 28 pg mL^?1 Cu²⁺, respectively. This method is rapid and precise with high sensitivity and good repeatability. The method has been applied to the determination of trace copper in tea and human hair with satisfactory results. Meanwhile, the mechanism for the determination of trace copper by catalytic fluorescence spectrophotometry using Cu(DP)²⁺ and Cu‐GPD‐4.0 was also discussed.     

Structure and Composition of the Anionic Chloride Complexes of Copper(II) as the Precursors of Catalysts for C–Cl Bond Metathesis

The chloride complexes of copper(II) (catalysts or catalyst precursors for various reactions of halogenated hydrocarbons) were characterized using electron, EPR, and EXAFS spectroscopy. It was found that chlorocuprates occur as mononuclear ([CuCl₄]^2–), binuclear ([Cu₂Cl₆]^2–), and, probably, polynuclear species in chlorobenzene solutions. The Cu–Cl bond length in [CuCl₄]^2– is 2.25 ± 0.2 Å, which is close to the same values for crystalline tetrachlorocuprates. It was assumed that the chloride complexes of copper with counterions occur as globules in chlorobenzene.     

Cu(II) and Cu(I) complexes with 2-(3,5-diphenyl-1H-pyrazole-1-yl)-4,6-diphenylpyrimidine: Synthesis and structure. Catalytic activity of Cu(II) compounds in reaction of ethylene polymerization

The Cu(II) and Cu(I) complexes with 2-(3,5-diphenyl-1H-pyrazole-1-yl)-4,6-diphenylpyrimidine (L) of the composition CuLX₂ (X = Cl, Br) and CuL(MeCN)Br are synthesized. According to X-ray diffraction data, the complexes have molecular structures. The molecules L are coordinated to the copper atom in bidentate-cyclic mode, i.e., through the N² atom of pyrazole and N¹ atom of pyrimidine rings. The coordination polyhedron of the Cu²⁺ ion in CuLX₂ compounds is completed to a distorted tetrahedron with halide ions, that of the Cu⁺ ion in CuL(MeCN)Br compounds, with the bromide ion and the nitrogen atom of acetonitrile molecule. The CuLX₂ complexes (X = Cl, Br) in combination with cocatalysts (methylaluminoxane and triisobutylaluminium) exhibit catalytic activity in ethylene polymerization.     

Cu2+-complexes of polyamino acids in aqueous solutions catalytic activity (H202-decomposition) and structure

The decomposition of H₂O₂ (8 · 10^?3M ) catalyzed by complexes of Cu²⁺ (4 · 10^?4M ) with various oligomers and polymers of glycine, L-lysine or L-glutamic acid was investigated in aqueous solution in the pH range 5–11, at 24°C and at low ionic strength. Previous investigations have shown that the decomposition of H₂O₂ is catalyzed by Cu²⁺-complexes capable of forming Cu²⁺-peroxocomplexes. With increasing pH the catalytic activity of Cu²⁺-complexes with glycine or glycylglycine (1:1) increases while the activity of Cu²⁺-complexes with tri- or tetraglycine (1:1) is comparatively small at higher pH values apparently because in the latter cases the coordination positions of the copper become progressively occupied by the peptides. This interpretation is in accordance with the pH-dependence of the light-absorption spectra of the latter complexes. Cu²⁺-complexes with poly-α, L -lysines of various molecular weights (molar ratios Cu²⁺: lysine residues = 1:15) have a catalytic activity comparable to or higher than that of the complex Cu²⁺-ethylenediamine (1:1), indicating two available coordination positions for formation of peroxo-complexes. On the other hand, the system Cu²⁺-L -lysine (1:15) showed no significant activity probably because all coordination positions at the Cu²⁺ are occupied by lysine. Despite the excess of ligand groups over Cu²⁺ in the polylysine systems the structure of this polyamino acid apparently does not allow its full coordination with these groups under the conditions investigated. Two adjacent chelating ε-amino groups are considered as the main ligand groups of the polymer to each copper ion. The Cu²⁺-poly-α, L -glutamic acid complex examined (Cu²⁺: glutamic acid residues = 1:5) shows comparatively little activity. In this case, absorption spectra indicate formation of hydroxo-complexes at higher pH. Besides the effects of structure, the electrostatic fields of the charged polyelectrolytes polylysine or polyglutamic acid are also considered to affect the rates of catalysis.     

Synthesis and characterization of copper(II) complexes of sulfadiazine with amino acids: catalytic activity toward oxidation of phenol and catechol

New copper complexes of DL-methioninoylsulfadiazine (MTS) and L-cystinoylsulfadiazine (CYS) were prepared and characterized using elemental analysis, IR, electronic spectroscopy, EPR spectroscopy, and thermal analysis. The mode of binding indicates that copper binds to MTS through carbonyl oxygen with the amino group nitrogen while for Cu^II–CYS the copper binds through carbonyl oxygen and SH with removal of its proton. The proposed structures were supported by conformational analysis which showed predominance of the trans form of copper(II)-L-cystinoylsulfadiazine. The two complexes enhanced oxidation of phenol and catechol in the presence of H₂O₂ under mild conditions. The catalyst shows proficiency toward oxidation of phenol and catechol compared to the auto-catalytic oxidation. Cu^II–MTS exhibited higher catalytic activity than Cu^II–CYS. The phenol and catechol oxidation is inhibited by Kojic acid.     

Total Oxidation of Propene and Toluene on Copper/Yttrium Doped Zirconia

The catalytic oxidation of propene and toluene has been investigated on pure ZrO₂, pure Y₂O₃, and ZrO₂ doped with 1, 5, and 10 mol % Y₂O₃ in the presence or absence of copper (0.5, 1, and 5 wt%). A synergetic effect has been detected since ZrO₂ and Y₂O₃ exhibit significantly lower activities than the mixed oxides. The higher surface areas, related to structural change from mononoclinic (ZrO₂) to tetragonal (ZrO₂–;;Y₂O₃), partly explained the higher activity of ZrO₂–;;Y₂O₃. However, it has been shown that the number of anionic vacancies, created by the substitution of Zr⁴⁺ by Y³⁺, in yttria-stabilized zirconia solids depends on the yttrium contents. Their effect on propene and toluene oxidation activity is significant. The anionic vacancies should induce better activity of the ZrO₂—5 mol % Y₂O₃ catalyst with or without copper, which presents the higher number of Zr³⁺ species. This support should favor the formation of CuO particles, which should be the most active catalytic sites in the studied reaction.     

Decomposition of H2O2 on copper-containing ion-exchange resins of the vinylpyridine series

By means of kinetic studies and EPR, it has been shown that, in the reaction of hydrogen peroxide decomposition in the presence of copper-containing anion-exchange resins of the vinylpyridine series AN-40, AN-25, and AN-251, the catalytic activity increases in a series of complexes of the following types: Cu(Py)₂ ²⁺3 ²⁺4 ²⁺. Increases in the degree of polymer cross-linking and increases in the content of copper complexes above 0.2 mg-ion/g lead to the appearance of steric hindrance to free diffusion of H₂O₂ molecules within the globules of resin, with a consequent decrease in specific catalytic activity of the ion-exchanger/metal complexes. It has been established by means of EPR and IR spectroscopy that in AN-25 and AN-251 CH₃ groups of the coordinated units are oxidized to carboxyl, with a consequent change in composition and structure of the Cu(II) complexes in the resins. Moreover, the copper ions are partly washed out from the resin into the reaction medium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1970–1975, September, 1989.     

Liquid-crystalline CuII and PdII complexes with nonmesogenic ferrocene-containing β-aminovinyl ketone

New liquid-crystalline heteropolynuclear complexes L₂M (M=Cu²⁺ (2a), Pd²⁺ (2b)) were synthesized by the reactions of C₅H₅FeC₅H₄−C₆H₄NH−C₂H₂−(CO)−C₆H₄OC₁₂H₂₅ (1, LH) with copper(ii) and palladium(ii) acetates. Compound2b was found to possess monotropic nematic and smectic phases;2a exhibits the monotropic nematic phase and a phenomenon of “double melting”. The compositions and structures of compounds1 and2a,b were established by elemental analysis,¹H and¹³C NMR, ESR, and IR spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 381–383, February, 1999.     

Carboxylate-bridged copper(II) complexes: synthesis,crystal structures,and superoxide dismutase activity

Two copper(II) complexes, [Cu₂(μ-benzoato)(L¹)₂]NO₃·2H₂O (1) and [Cu₂(μ-succinato)(L²)₂(H₂O)]ClO₄ (2), have been synthesized, where L¹ = N′-[(E)-phenyl(pyridin-2-yl)methylidene]benzoylhydrazone and L² = N′-[(E)-pyridin-2-ylmethylidene]benzoylhydrazone. These complexes were characterized including by single-crystal X-ray diffraction studies. The copper is five-coordinate in 1 while in 2 one copper is five-coordinate and the other is six-coordinate. Electrochemical behavior of these complexes was measured by cyclic voltammetry. The conproportionation equilibrium constants (K_con) for both complexes have been estimated. The superoxide dismutase (SOD) activities of 1 and 2 were measured by nitro blue tetrazolium assay. Complex 1 has better SOD activity than 2.     

Darstellung und einige Eigenschaften von Kupfer(I)-Kupfer(II)-Selenocyanaten

Preparation and Some Characteristics of Copper(I)-Copper(II) Selenocyanates From the system Cu²⁺-H₂O-en-SeCN-in dependence on the conditions two new complexes have been prepared: Cu₃en₂(SeCN)(CN)₃· H₂O(I) and Cu₃en₂(SeCN)₂(CN)₂· H₂O(II). They were studied by the methods of infra-red and EPR spectra as well as by those of X-ray diffraction. It has been found that Cu₂₊ is coordinated in these complexes with two molecules of ethylene diamine and one molecule water. The anion ligands have a bridging function and coordinate the copper(I). The EPR spectra show that the two complexes exhibit around the atom Cu²⁺ have different ligand field symmetry. For complex (I) it is a typically axial spectrum with two values of the gfactor g⊥? 2.18 and g⊥? 2.05 while complex (II) has an asymmetrical isotropic spectrum with one g-factor value only g⊥? 2.07.     

NC Palladacycles and C,C-chelating phosphorus ylide complexes: synthesis,X-ray characterization,and comparison of the catalytic activity in the Suzuki-Miyaura reaction

Six secondary amine palladacycles bearing monodentate ligands (1a, 2a), 1,2-bis(diphenylphosphino)ethane (dppe) and 1,3-bis(diphenylphosphino)propane (dppp) containing bridging and bidentate ligands (1b, 2b–d), and four C,C-type phosphorus ylide complexes containing thiourea (tu) (3a), phenyl isothiocyanate (4a), and bridging and terminal azide groups (5 and 5a) have been synthesized. Resulting complexes have been characterized by elemental analyses, IR, ¹H-, ¹³C{¹H}-, and ³¹P{¹H}-NMR spectroscopy with single crystal X-ray structure determination of 1a and 2a. The Pd in 1a and 2a occupies the center of a slightly distorted square planar environment formed by C_aryl, N_amine, N_pyridine, and Cl. The catalytic efficiency of complexes showed that in most cases, amine palladacycles display better catalytic activities than the phosphorus ylide Pd(II) complexes. Comparison between bidentate and bridging dppe complexes showed that dppe-bridged dimer 2d has higher catalytic activity than dppe bidentate complex.     

Two Trinuclear CuII Complexes: Effect of Phosphonate Ligand on the Magnetic Property and Electrocatalytic Reactivity for Water Oxidation

Two trinuclear copper phosphonate complexes, [Cu₃(pda)₃(tBuPO₃)]?2(Et₃NH) ( 1 ) and [Cu₃(pda)₃(PhPO₃)]?2(Et₃NH) ( 2 ), have been synthesized and investigated by a combination of X‐ray crystallography, PXRD, magneto‐ and electrochemistry, EPR, in situ UV‐vis spectroelectrochemistry and DLS. The two complexes feature almost identical crystal structures, the anions of which are both supported by pda^2? and tBuPO₃^2?/PhPO₃^2? groups, bridging three five‐coordinated Cu^II atoms to form a crown‐like structure. This is the first time that trinuclear copper phosphonate complexes have been isolated and characterized. Magnetic susceptibility measurements reveal that complexes 1 and 2 both display overall ferromagnetic characters, but with different exchange interactions between the metal ions within the two clusters. The electrocatalytic activity for water oxidation of the two complexes was preliminarily investigated, which reveals that both of the two complexes can carry out electrocatalytic water oxidation in a neutral system owing to the introduction of phosphonate ligands into the complexes, with a TOF of about 0.82 s^?1 ( 1 ) and 0.58 s^?1 ( 2 ), respectively. We propose that the presence of phosphonate ligands may affect the magnetic property and catalytic activity of the complexes.