Study on thermal decomposition of copper(II) acetate monohydrate in air

The thermal decomposition of copper(II) acetate monohydrate (CuAc₂·H₂O) under 500 °C in air was studied by TG/DTG, DTA, in situ FTIR and XRD experiments. The experimental results showed that the thermal decomposition of CuAc₂·H₂O under 500 °C in air included three main steps. CuAc₂·H₂O was dehydrated under 168 °C; CuAc₂ decomposed to initial solid products and volatile products at 168–302 °C; the initial solid products Cu and Cu₂O were oxidized to CuO in air at 302–500 °C. The copper acetate peroxides were found to form between 100 and 150 °C, and the dehydration of these peroxides resulted in the presence of CuAc₂·H₂O above 168 °C. The initial solid products were found to be the admixture of Cu, Cu₂O, and CuO, not simply the single Cu₂O as reported before. Detailed reactions involved in these three steps were proposed to describe the complete mechanism and course of the thermal decomposition of CuAc₂·H₂O in air.     

Semiempirical dynamic phase diagrams of nanocrystalline products during copper (II) acetylacetonate vapour decomposition

Nanoparticle production by Cu(acac)₂ vapour decomposition was studied. The composition of the produced particles varied from Cu to Cu₂O depending on experimental conditions. In order to explain the crystalline phase behaviour, a kinetic model to build a semiempirical dynamic phase diagram of the products was proposed. Prevailing role of copper dimers in the processes of copper and copper (I) oxide particle growth was demonstrated. The composition of products was determined by reactions on the surface of growing particles and depended on the ratio of gaseous species. The calculated dynamic phase diagrams were in excellent agreement with the experimental results.     

Plasma-assisted oxidation of Cu(100) and Cu(111)

Oxidized copper surfaces have attracted significant attention in recent years due to their unique catalytic properties, including their enhanced hydrocarbon selectivity during the electrochemical reduction of CO₂. Although oxygen plasma has been used to create highly active copper oxide electrodes for CO₂RR, how such treatment alters the copper surface is still poorly understood. Here, we study the oxidation of Cu(100) and Cu(111) surfaces by sequential exposure to a low-pressure oxygen plasma at room temperature. We used scanning tunnelling microscopy (STM), low energy electron microscopy (LEEM), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and low energy electron diffraction (LEED) for the comprehensive characterization of the resulting oxide films. O₂-plasma exposure initially induces the growth of 3-dimensional oxide islands surrounded by an O-covered Cu surface. With ongoing plasma exposure, the islands coalesce and form a closed oxide film. Utilizing spectroscopy, we traced the evolution of metallic Cu, Cu₂O and CuO species upon oxygen plasma exposure and found a dependence of the surface structure and chemical state on the substrate''s orientation. On Cu(100) the oxide islands grow with a lower rate than on the (111) surface. Furthermore, while on Cu(100) only Cu₂O is formed during the initial growth phase, both Cu₂O and CuO species are simultaneously generated on Cu(111). Finally, prolonged oxygen plasma exposure results in a sandwiched film structure with CuO at the surface and Cu₂O at the interface to the metallic support. A stable CuO(111) surface orientation is identified in both cases, aligned to the Cu(111) support, but with two coexisting rotational domains on Cu(100). These findings illustrate the possibility of tailoring the oxidation state, structure and morphology of metallic surfaces for a wide range of applications through oxygen plasma treatments.

A low-pressure oxygen plasma oxidized Cu(100) and Cu(111) surfaces at room temperature. The time-dependent evolution of surface structure and chemical composition is reported in detail for a range of exposure times up to 30 min.     

Zeolite ZSM-5 containing copper ions: The effect of the copper salt anion and NH<Subscript>4</Subscript>OH/Cu<Superscript>2+</Superscript> ratio on the state of the copper ions and on the reactivity of the zeolite in DeNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir’s monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in N₂O decomposition. The amount of Cu²⁺ that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu²⁺ cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO _x ) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO _x properties of Cu-ZSM-5 depend considerably on the NH₄OH/Cu²⁺ ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NH₄OH/Cu²⁺ = 6–10 stabilize, in the Cu-ZSM-5 structure, Cu²⁺ ions bonded with extraframework oxygen, which are more active in DeNO _x than isolated Cu²⁺ ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NH₄OH/Cu²⁺ = 3).     

Thermal decomposition of basic cobalt and copper carbonates

Basic cobalt and copper carbonates were prepared by precipitation from solutions of their nitrates using KHCO₃ at room temperature in CO₂ atmosphere. The thermal decomposition of the prepared basic carbonates was studied by means of TG and DTA techniques and the phases produced were identified by XRD measurements. The products obtained at 400C were subjected to different doses of gamma-rays (40–160 M rad) and the thermal stabilities of these solids were investigated.The results obtained revealed that basic cobalt carbonate decomposed at 335C to produce Co₃O₄ which remained stable up to 850 and then decomposed above this temperature giving CoO which transformed into Co₃O₄ on cooling to room temperature. Basic copper carbonate dissociated at 290C yielding CuO which yielded Cu₂O and metallic copper at 1060 and 1150C, respectively. However, the produced cuprous oxide and metallic copper solids were converted into CuO and CU₂O, respectively by cooling in air to room temperature.Gamma-irradiation decreased the thermal stability of Co₃O₄ to an extent proportional to the dose employed. On the other hand, this treatment increased the thermal stability of both CuO and Cu₂O.     

A Polarographic Method Determing Cu(II), Cu(I) and Metallic Copper Contents in Copper Oxide Samples

Abstract

A polarographic procedure was developed which permits the analysis of powdered cupric and cuprous oxides in the presence of metallic copper. To determine CuO, Cu₂O and metallic copper content in the sample two weight aliquots were used. The first aliquot was dissolved in medium of 50 % ethanol + 3 M hydrochloric acid + saturated ascorbic acid solution. Insoluable metallic copper was determined polarographically after its' separation and additional dissolving in concentrated nitric acid.

The second sample aliquot was dissolved in 6 M hydrochloric acid and the ratio of Cu(I) / Cu(II) in the solution was determined from the polarographic curves. To calculate CuO, Cu₂O and Cu content in a sample the proposed procedure was applied. The developed method provides the accurate results of the determination of CuO, Cu₂O and Cu content in a powdered mixture. The reproducibility expressed as the relative standard deviation is from 1 % to 5 %.     

Effect of copper precursors on the catalytic activity of Cu/ZSM-5 catalysts for selective catalytic reduction of NO by NH<Subscript>3</Subscript>

The Cu/ZSM-5 catalysts prepared by different copper precursors were used for the selective catalytic reduction (SCR) of NO _x with NH₃. The Cu/ZSM-5 catalyst prepared by the copper nitrate (Cu/ZSM-5-N) presented the best performance among the Cu/ZSM-5 catalysts and showed above 90 % NO _x conversion at 225–405 °C. The average particle size of CuO was 5.82, 9.20, and 11.01 nm over Cu/ZSM-5-N, Cu/ZSM-5-S (prepared by copper sulfate), and Cu/ZSM-5-C (prepared by copper chloride), respectively. The Cu/ZSM-5-N catalyst showed the highly dispersed copper species, the strong surface acidity, and the excellent redox ability compared with the Cu/ZSM-5-C and Cu/ZSM-5-S catalysts. The Cu⁺ and Cu²⁺ existed in the Cu/ZSM-5 catalysts and the abundant Cu⁺ over Cu/ZSM-5-N might be responsible for the superior SCR activity.     

Copper and copper oxides nanopowders in the oxidative condensations of phenylacetylene and <Emphasis Type="Italic">tert</Emphasis>-butylacetylene

Transformations of phenylacetylene and tert-butylacetylene in the presence of copper and copper oxide (Cu₂O, CuO) nanopowders prepared by gas-phase condensation of copper in argon were studied. The reaction of phenylacetylene with copper oxide nanopowders having different phase compositions in the absence of a solvent at room temperature resulted in oxidative condensation of phenylacetylene and complex formation of the condensation product. The complex undergoes decomposition by the action of acids, bases, and compounds capable of forming complexes. According to the X-ray diffraction data, one of the products is a new “parquet” modification of diphenyldiacetylene. Under analogous conditions, tert-butylacetylene gave rise to a complex mixture of products among which di-tert-butyldiacetylene was identified by gas chromatography-mass spectrometry. No copper complexes with the tert-butylacetylene condensation products were detected.     

Synthesis,structure and spectral studies on mixed ligand copper(II) complexes of diimines and acetylacetonate

Two new mixed ligand complexes of copper(II) with acetylacetonate (acac), 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) belonging to the class of cytotoxic and antineoplastic compounds known as CASIOPEINAS^® were synthesized and structurally characterized. Crystals of both complexes [Cu(acac)(bpy)(H₂O)]NO₃ · H₂O (1), [Cu(acac)(phen)Br] (2) contain square pyramidal Cu(II) complex species. In frozen solution both compounds give well resolved EPR spectra with very similar parameters.     

Thermal oxidative degradation of isotactic polypropylene catalyzed by copper and copper oxide interfaces

The oxidative degradation of isotactic polypropylene films coated on well-defined Cu(Cu₂O), CuO_0.67, and CuO films in a temperature range of 90–120°C in a quartz-spoon-gauge-reaction vessel was studied. This catalytic reaction has been compared with the oxidation of polypropylene without copper or oxide films. The reaction vessel contained, if needed, P₂O₅ and/or KOH as “getters” for H₂O and CO₂, these substances could be menitored continuously. Cu(Cu₂O) films were transformed during oxidation of the polymer to yellow CuO_0.67 below 100°C and above this temperature to black CuO in the presence of H₂O and CO₂, whereas in the absence of these compounds CuO was formed below 100°C and CuO_0.67 at 120°C. Characteristic autoxidation curves obtained in the absence of H₂O and CO₂ showed induction periods that were shorter for copper oxide-polymer interfaces than for glass-polymer interfaces (i.e., for uncatalyzed oxidation). Abnormalities were observed for Cu(Cu₂O)-polymer interfaces because of further oxidation of Cu during the reaction. The rates of oxygen consumption were faster for CuO_0.67-polymer and CuO-polymer than for the uncatalyzed reaction; the catalytic action of CuO_0.67 was somewhat larger than that of CuO. The important observation was made that the mechanism of oxidation is not the same in the absence and presence of reaction products; that is, H₂O and CO₂. This was confirmed by ion beam scattering experiments, which also revealed that an oxidation-reduction process takes place at Cu and their oxide interfaces. A mechanism for the catalytic oxidation process, based on the ease by which copper ions are released from the metal oxides at the interface, was formulated. These ions diffuse subsequently as actions of carboxylate anions into the bulk of the polymer. Arrhenius equations of oxygen consumption are given for all cases; the energy of activation calculated for the initiation of the uncatalyzed oxidation agrees with its literature value. The energy of activation for the initiation of the catalyzed reaction was a few kilocalories lower than that for the uncatalyzed reaction. Catalytic action is mainly operative for the initiation reaction at the interface and for the decomposition of hydroperoxides by copper ions. Preventing the delivery of copper ions to the polymer would be the most efficient way of inhibiting the catalysis.     

Thermal decomposition of ammonium perchlorate in the presence of bimetallic additives

The catalytic activity of the thermolysis products of double complex compounds in the decomposition reaction of ammonium perchlorate was studied. The products used are C_1.4N_1.6H₃CoFe (I), C₆N₈Co₄Fe₃ (II), O₁₁Co₄Fe₃ (III), O_8.5(CN)_0.3Cu₃Fe₂ (IV), and reactive CuO. All active phases decrease the temperature of complete decomposition of NH₄ClO₄, and the order of temperature decreasing is the following: I ≈ II (120 °C) > IV > III (80 °C) ? CuO.     

Copper(II)–Ammonia Complexation Equilibria in Aqueous Solutions at Temperatures from 30 to 250°C by Visible Spectroscopy

The spectra of copper(II)–ammonia solutions in 2 mol-kg^–1 NH₄NO₃(aq) were recorded as a function of pH with a new UV–visible flow cell, capable of operating at conditions up to 325°C and 300 bars. Equilibrium constants for the formation of copper(II)–ammonia complexes Cu(NH₃)_n ²⁺, 1 n 4, from 30 to 150°C were determined by evolving factor analysis and nonlinear least-squares regression. Measurements at higher temperatures were limited by thermal decomposition of NH₄NO₃(aq). The formation constants of Cu(NH₃)_n ²⁺ decrease with temperature, consistent with extrapolations of literature data from measurements below 100°C. Measurements above 150°C were carried out in 0.5 mol-kg^–1 CF₃SO₃H (aq), at the very high ammonia concentrations required to avoid the precipitation of CuO(s). The spectra are consistent with Cu(NH₃)₄ ²⁺ as the predominant species, based on extrapolations of peak maxima and molar absorptivities from lower temperatures. Shifts in the spectra of Cu²⁺ and the Cu(NH₃)_n ²⁺ species to higher wavelength and increases in molar absorbance with increasing temperature are discussed in terms of the structure of the complexes.     

XPS,UPS, and STM studies of nanostructured CuO films

A Cu₁O_1.7 oxide film containing a large amout of superstoichiometric oxygen was obtained by low-temperature oxidation of metallic copper in the oxygen plasma. An STM study of the film structure showed that ～10 nm planar copper oxide nanocrystallites with particles packed parallel to the starting metal surface. In an XPS study, the spectral characteristics of the Cu2p and O1s lines indicated that particles with a CuO lattice formed (E _bnd(Cu2p _3/2) = 933.3 eV and a shake-up satellite, E _bnd(O1s) = 529.3 eV). The additional superstoichiometric oxygen is localized at the sites of contact of nanoparticles in the interunit space and is characterized by a state with the binding energy E _bnd(O1s) = 531.2 eV. Due to the formation of a nanostructure in the films during low-temperature plasma oxidation, the resulting copper oxide has a much lower thermal stability than crystalline oxide CuO.     

Thermal decomposition of basic copper sulphate monohydrate

The thermal decomposition of copper sulphate hydroxide hydrate, (CuO·CuSO₄). 2Cu(OH)₂·H₂O, to copper oxysulphate and CuO was investigated by X-ray phase analysis, IR spectroscopy, complex thermal analysis and electron microscopy. The effect of water vapour and time of treatment on the formation of decomposition products with a large surface area is studied. The strong decrease in specific surface area of the precipitate (from 80 m²/g to 20 m²/g) thermally treated at a temperature above 250°C is associated with the elimination of water having a coordination bond with the Cu²⁺ ion. During this process, the interplanar distances of the crystal lattice of copper sulphate hydroxide hydrate decrease. The time of decomposition of this compound essentially affects the decrease of the specific surface area. When the decomposition proceeds in an atmosphere containing water vapour sintering processes are predominating and the phase obtained has a considerably smaller specific surface area than in cases of decomposition under dry air.     

Thermal behaviour of precursors for CuInS2 thin films deposited by spray pyrolysis

The thermal decomposition of precursors for copper indium disulphide (CuInS₂) thin films obtained by drying aqueous solutions of copper chloride (CuCl₂), indium chloride (InCl₃) and thiourea (SC(NH₂)₂) at the Cu:In:S molar ratios of 1:1:3 (1) and 1:1:6 (2) was monitored by simultaneous thermogravimetry /differential thermal analysis/ evolved gas analysis-mass spectrometry (TG/DTA/EGA-MS) measurements in a dynamic 80 %Ar + 20 %O₂ atmosphere. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to characterise the dried precursors and products of the thermal decomposition. The precursors 1 and 2 are mixtures of copper and indium chloride thiourea complex compounds, whilst 1 can also contain unreacted InCl₃. The thermal degradation of 1 and 2 in the temperature range of 30–800 °C consists of six steps with a total mass loss of 71.5 and 89.8 %, respectively. According to XRD, CuInS₂ is formed below 300 °C. Decomposition of 1 and 2 is completed at 620 and 600 °C, respectively. The final decomposition product of 1 at 800 °C consists of a mixture of In₂O₃ and CuO phases, whilst 2 consists of In₂O₃, CuO and Cu₂In₂O₅ phases. EGA by MS revealed the release of CS₂, NH₃, H₂NCN and HNCS, which upon their oxidation also yield COS, SO₂, HCN and CO₂.     

Studies of the effects of copper, copper(II) oxide and copper(II) chloride on the thermal degradation of poly(vinyl chloride)

Investigations of the pyrolysis of poly(vinyl chloride) (PVC) in the presence of copper metal (Cu), copper(II) oxide (CuO) and copper(II) chloride (CuCl₂) are of potential importance because of the likelihood of the formation of these copper compounds during the thermal degradation of PVC-coated copper wires, a step in the recovery of copper from waste. The presence of Cu, CuO and CuCl₂ (i) retards the thermal degradation of PVC in air and in nitrogen and (ii) decreases the percentages of volatile products produced at both stages of the decomposition. These effects are greatest for PVC-CuO. The presence of copper, CuO or CuCl₂ in PVC has a major effect on the nature of the gaseous emissions of the thermal decomposition in air and in nitrogen. The concentrations of total chlorine, aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons and soot particulates are all affected relative to an equivalent amount of PVC. These changes are greatest for the PVC-CuO system for which total chlorine emissions in air and nitrogen are reduced by 40% in air and 20% in nitrogen, benzene emissions are reduced by greater than 90% in air and nitrogen, other aromatic and chloroaromatic emissions are reduced, and soot particulate emissions are reduced by more than 50% as the concentrations of aliphatic compounds are increased. These changes are consistent with the presence of copper or its compounds permitting more efficient combustion of the carbon content of the PVC and particularly in the case of PVC-CuO with the removal of chlorine during pyrolysis in the inorganic phase.     

Formation of nanoparticles of a new metastable copper compound in the copper acetate hydrate/poly(acrylonitrile) heterogeneous system

We use X-ray powder diffraction to study heterogeneous solid-phase reactions induced by IR radiation in the system Cu(OOCCH₃)₂·H₂O/PAN and intermediate copper compounds in the synthesis of copper nanoparticles. The composite Cu(OOCCH₃)₂ · H₂O/PAN after annealing contains crystallites of copper (l _Cu = 16 nm), a new metastable compound Cu _x>2O ( $ l_{Cu_{x > 2} O} We use X-ray powder diffraction to study heterogeneous solid-phase reactions induced by IR radiation in the system Cu(OOCCH₃)₂·H₂O/PAN and intermediate copper compounds in the synthesis of copper nanoparticles. The composite Cu(OOCCH₃)₂ · H₂O/PAN after annealing contains crystallites of copper (l _Cu = 16 nm), a new metastable compound Cu _x>2O ( = 20 nm), and Cu₂O ( = 20 nm). After 45 days of air exposure, the intensity of Cu _x>2O reflections in the composite decreases dramatically, whereas that of copper reflections increases. Cu _x>2O has a monoclinic unit cell with the parameters a = 5.424, b = 3.196, c = 3.072 ?, β = 119.51°. Original Russian Text ? V.M. Novotortsev, V.V. Kozlov, Yu.M. Korolev, G.P. Karpacheva, L.V. Kozhitov, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 7, pp. 1087–1089.     

Reactivity of binary mixtures of Cu(II) oxalate and La(III) oxalate

Reactivity of binary mixtures of oxalates of Cu(II) and La(III) was studied by observing their thermal behaviours in decomposition using TG, DTA and XRD techniques to set the temperature conditions for preparations of various composites of oxides of Cu(II) and La(III). In the thermal behaviour it was found that the decomposition of Cu(II) oxalate is not affected while that of La(III) oxalate is drastically affected in the case of all the mixtures. The decomposition temperature at which La(III) oxide is formed is lowered by 250 K in the case of all the mixtures while the complete decomposition occurred at 723 K only in the case of mixtures containing excess Cu(II) oxalate.At 823 K La₂CuO₄ phase is developed in all the mixtures while -La and Cu₂La phases are also detected in mixtures containing excess Cu(II) oxalate. Therefore, the temperature 823 K was found to be suitable to prepare various composites viz. La₂CuO₄, La₂CuO₄·La₂O₃ and La₂CuO₄·CuO to study their electrical properties.Authors are thankful to the authorities of Department of Atomic Energy (DAE), Government of India, for providing the funds for research project and to Professor A. V. Phadke, Department of Geology, University of Poona, for valuable discussion.     

Production of hydrogen by oxidative steam reforming of methanol over Cu/SiO2 catalysts

Selective production of hydrogen by oxidative steam reforming of methanol (OSRM) was studied over Cu/SiO₂ catalyst using fixed bed flow reactor. Textural and structural properties of the catalyst were analyzed by various instrumental methods. TPR analysis illustrates that the reduction temperature peak was observed between 510?K and 532?K at various copper loadings and calcination temperatures and the peaks shifted to higher temperature with increasing copper loading and calcination temperature. The XRD and XPS analysis demonstrates that the copper existed in different oxidation states at different conditions: Cu₂O, Cu⁰, CuO and Cu(OH)₂ in uncalcined sample; CuO in calcined sample: Cu₂O and metallic Cu after reduction at 600?K and Cu⁰ and CuO after catalytic test. TEM analysis reveals that at various copper loadings, the copper particle size is in the range between 3.0?nm and 3.8?nm. The Cu particle size after catalytic test increased from 3.6 to 4.8?nm, which is due to the formation of oxides of copper as evidenced from XRD and XPS analysis. The catalytic performance at various Cu loadings shows that with increasing Cu loading from 4.7 to 17.3?wt%, the activity increases and thereafter it decreases. Effect of calcination shows that the sample calcined at 673?K exhibited high activity. The O₂/CH₃OH and H₂O/CH₃OH molar ratios play important role in reaction rate and product distribution. The optimum molar ratios of O₂/CH₃OH and H₂O/CH₃OH are 0.25 and 0.1, respectively. When the reaction temperature varied from 473 to 548?K, the methanol conversion and H₂ production rate are in the range of 21.9–97.5% and 1.2–300.9?mmol?kg^?1?s^?1, respectively. The CO selectivity is negligible at these temperatures. Under the optimum conditions (17.3?wt%, Cu/SiO₂; calcination temperature 673?K; 0.25 O₂/CH₃OH molar ratio, 0.5 H₂O/CH₃OH molar ratio and reaction temperature 548?K), the maximum hydrogen yield obtained was 2.45?mol of hydrogen per mole of methanol. The time on stream stability test showed that the Cu/SiO₂ catalyst is quite stable for 48?h.