Copper Manganese Spinel Research Articles

Optimization of electrophoretic deposition and thermal treatment of Cu–Mn spinel matrix for spinel/perovskite composite coating used as SOC metallic interconnect

The electrophoretic deposition of a mixture of copper-manganese spinel oxide matrix with perovskite oxide dispersion phase and subsequent two-step sintering was investigated as a means of obtaining a new spinel/perovskite composite coating for application in metallic interconnects for solid oxide cell (SOC) technologies. The effect of a number of factors was examined, including electrophoretic deposition parameters such as solvent type, time, voltage, and dispersant content as well as different heat treatment conditions on the quality of the matrix of the coating material. A solution of ethanol-acetone (25/75 v/v) and 2.0 g L−1 of iodine dispersant with a deposition time of 60 s and a voltage of 60 V provided the thickest, most uniform coating as deposited. SEM observations showed that a dense coating of Cu–Mn spinel was obtained after 8 h of reduction at 1000 °C followed by 6 h of oxidation at 850 °C. Selected preparation parameters were applied to deposit composite coatings with a Cu–Mn spinel matrix and the addition of LNF, LSC and LSCF perovskites.

Selective catalytic reduction of NO with NH3 over copper-manganese spinel oxides at low temperature: effects of calcination temperature and dispersant

Selective catalytic reduction of NO with NH3 over copper-manganese spinel oxides at low temperature: effects of calcination temperature and dispersant

Oxygen vacancy engineering on copper-manganese spinel surface for enhancing toluene catalytic combustion: A comparative study of acid treatment and alkali treatment

Copper-manganese spinel is a low-cost VOCs catalytic combustion catalyst with good performance. Oxygen vacancy has excellent properties for oxygen activation and VOCs dehydrogenation activation, which is beneficial for the catalytic combustion of VOCs. In this study, a large number of oxygen vacancies were introduced on the copper-manganese spinel surface by selective dissolution method (acid treatment and alkali treatment) for catalytic combustion of toluene. Furthermore, the effects of acid treatment and alkali treatment on the catalytic performance, oxygen vacancy amount, physical and chemical properties, and toluene catalytic combustion mechanism of copper-manganese spinel were studied. Both acid treatment and alkali treatment can produce large quantities of oxygen vacancies on the copper-manganese spinel surface. The generation of surface oxygen vacancies can greatly improve the catalytic combustion activity of copper-manganese spinel. At 240 °C, the combustion rate of toluene increased by 8.8 times for the acid-treated catalyst and 11.2 times for the alkali-treated catalyst. The numerous surface oxygen vacancies, Mn3+/Mn4+ at the ratio of 1.11 and appropriate acidity result in the alkali-treated catalyst exhibiting excellent catalytic activity and stability for toluene combustion. This strategy provides a new method to further improve catalytic combustion activity of copper-manganese spinel and a reference for the development of the surface oxygen vacancy engineering of transition metal oxides.

Control of the mechanism of chemical-looping of ethanol in non-stoichiometric ferrites by Cu-Mn substitution

Copper-manganese spinel ferrites have been evaluated as solid oxygen carriers for the production of hydrogen from water by ethanol-steam redox cycles. The materials were characterized by X-ray diffraction, Mössbauer spectroscopy, temperature-programmed reduction, oxygen isotope exchange and textural analysis. Surface reactions were followed by DRIFT spectroscopy. The amount and purity of hydrogen, produced in redox cycles at constant temperature of 450 °C, were highly affected by the nature of the oxygen carrier phases in the reduction step of the cycle. Cu-rich ferrites were reduced by ethanol to metallic copper and iron carbides, whereas Mn-rich ferrites were less deeply reduced to manganowustite. Ethanol was mainly oxidized by Cu-ferrites to CO and CO2, while mainly oxydehydrogenation products were formed on Mn-ferrites. In the reoxidation of the oxygen carrier by steam, the production of CO and CO2 by oxidation of carbides negatively affected the purity of the hydrogen formed.

Microwave-assisted removal of benzene with high efficiency on cobalt modified copper-manganese spinel oxides

Microwave-assisted process has been demonstrated to have immense potential for promoting chemical reactions and reducing energy consumption. In this study, catalytic oxidation of benzene was carried out over Co-Cu-Mn mixed oxides (CoxMn1−xCuOy) under microwave irradiation. The spinel-type mixed oxides were mainly formed for the Co-Cu-Mn mixed oxides with different Co/Mn ratios. The substitution of Mn sites by Co was confirmed by Fourier and Wavelet transformed extended x-ray absorption fine structure spectra. As the Co/Mn ratio increased, the heating characteristics of the catalysts under microwave irradiation monotonically improved. The benzene oxidation activity increased on the Co/Mn ratio of 2/3 due to the enhanced specific surface area, benzene adsorption properties, and lattice-oxygen reactivity. Microwave inducing significantly lowered the reaction temperature required for benzene oxidation. Co0.4Mn0.6CuOy completely oxidized benzene at a relatively low microwave power compared to pristine Cu-Mn oxides. The Co-Cu-Mn oxides showed high activity and stability for benzene oxidation even under humid conditions. Combining pre-adsorption and thermal oxidation processes on Co0.4Mn0.6CuOy improved the low concentration of benzene oxidation efficiency by rapid microwave heating. The compound of Co0.4Mn0.6CuOy and Co0.8Mn0.2CuOy mixed at 3:1 showed even higher activity than Co0.4Mn0.6CuOy.

An electrophoretic co-deposition of metal oxides followed by in-situ copper manganese spinel synthesis on AISI-430 for application in SOFC interconnects

Electrophoretic co-deposition of copper and manganese oxides followed by in-situ reactive sintering is investigated as a method of Cu–Mn spinel coating for application in SOFC interconnects. Effect of electrophoretic deposition parameters including time, voltage, solid concentration and dispersant content on the quality and quantity of deposition are examined. A uniform layer of oxides is co-deposited at 100 V, in 10 min, with 10 g/L oxides in ethanol-acetone solution and 1:16 w/w dispersant:oxides. Based on XRD and SEM-EDS results, rate of Fe and Cr diffusion is unacceptable at above 850 °C. 3 h of sintering in air at 800 and 850 °C is best to synthesize spinel without severe Fe–Cr contamination. In a 100-h cyclic oxidation test, coatings prevent chromium poisoning and reduce the oxidation rate by a minimum of two orders of magnitude decrease in the parabolic rate constant of oxidation from 1.34 × 10−12 in uncoated to 8.50 × 10−14 g2 cm−4 s−1 and 32.3% decrease in Cr at.% in the coated samples.

Cu1.5Mn1.5O4 spinel type composite oxide modified with CuO for synergistic catalysis of CO oxidation

Composite oxides of copper and manganese are widely used in oxidation reactions, and the main active component is copper-manganese spinel, whereas the copper oxide and manganese oxide show extremely low activity, despite that they are beneficial for CO oxidation. In this paper, it was found that the synergistic effect of Cu1.5Mn1.5O4 and CuO can promote the catalytic oxidation of CO. The catalysts were prepared using the citric acid complexation method and they were characterized through combined the techniques of N2-adsorption desorption, XRD, H2-TPR, TEM, CO-TPD and O2-TPD. The catalytic performance of various catalysts in CO oxidation was then evaluated. The results confirmed that Cu1.5Mn1.5O4 modified with CuO exhibited the best catalytic performance and the highest unit surface activity (defined as the CO conversion rate per unit surface area of catalyst). CuO and Cu1.5Mn1.5O4 had a synergistic effect, where O2 was activated by CuO and it then interacted with CO, activated by Cu1.5Mn1.5O4, to form CO2, thus increasing the catalytic activity.

Co-precipitated Cu-Mn mixed metal oxides as oxygen carriers for chemical looping processes

Chemical looping with oxygen uncoupling (CLOU) and chemical looping air separation (CLAS) are novel and potentially promising processes for the combustion of solid fuels (e.g. biomass) for power generation with inherent CO2 capture. Redox-experiments at 850–950 °C confirmed that copper manganese spinel oxides are promising oxygen carriers for these processes, as they combine a relatively high O2 release capacity and fast O2 release kinetics. Furthermore, this work presents a novel method to calculate the O2 partial pressure equilibrium and the heat of O2 release from observed rates of reaction. To demonstrate this method, oxygen carriers were prepared via mechanical mixing and co-precipitation with varying molar Cu:Mn ratios and synthesis conditions, thereby tuning material properties and the pore structure. The precursors and calcined materials were characterised, and the crystalline phases were determined using X-ray diffraction. The insights from the post cycling analysis of the oxygen carriers and the experimentally obtained O2 release capacities were combined to elucidate the redox-reactions relevant for the two processes. It was found that the presence of a higher partial pressure of O2 during the O2 release results in the formation of different (perovskite-like) phases than those occurring during the decomposition in an O2-free environment. The oxygen carriers demonstrated excellent stability at CLOU and CLAS process conditions during extended redox cycling (100 cycles in a thermo-gravimetric analyser and 50 cycles in a fluidised bed reactor), showing no significant loss of reactivity or O2 release capacity and a high resistance towards attrition and agglomeration. The degree of degradation after 100 cycles was in the order: temperature swing (CLAS) < O2 partial pressure swing (CLOU) < reduction with CH4 (chemical looping combustion).

Electrophoretically Deposited Copper Manganese Spinel Coatings for Interconnections in Solid Oxide Fuel Cells

Chromium poisoning of the cathode due to oxidation of metallic interconnections and subsequent formation of vapor phase chromium containing species is a well-known problem. The application of ceramic coatings on the interconnections to prevent this deleterious phenomenon is currently being extensively investigated. Copper manganese spinel coatings of different compositions were deposited on Crofer 22 APU substrates containing grooves, by electrophoretic deposition (EPD). Thermo-gravimetric measurements under oxidizing conditions at 800°C were carried out to study the effectiveness of the coatings as diffusion barriers. Special attention was paid to coating thickness variations and adhesion around corners and the vertical walls of the grooves. Chromium diffusion into the spinel coatings as well as area specific resistance of the coatings at 800°C are reported.

Facile synthesis of copper-manganese spinel anodes with high capacity and cycling performance for lithium-ion batteries

Copper-manganese spinel containing anodes were synthesized by a facile sol-gel method and evaluated in lithium-ion battery applications for the first time. The synergistic effects between copper-manganese and the aqueous binder (sodium carboxymethyl cellulose) provided a high specific capacity and excellent cycling performance. It was found that the specific capacity of the copper-manganese spinel remained at 608mAhg−1 after 100 cycles at a current density of 200mAg−1. Furthermore, a relatively high reversible capacity of 278mAhg−1 could be obtained at a current density of 2000mAg−1, indicating a good rate capability. These studies suggest that copper-manganese spinel is a promising material for lithium-ion battery applications due to a combination of good electrochemical performance and low cost.

Copper–Manganese Spinel Oxide Catalyzed Synthesis of Amides and Azobenzenes via Aminyl Radical Cations

AbstractA highly efficient Cu–Mn‐catalyzed process for the aminolysis of esters was developed. Also, the catalyst promoted the self‐ and cross‐dehydrogenative coupling of anilines to generate symmetrical and unsymmetrical azobenzenes, respectively. The reactions were performed under neutral conditions with an inexpensive catalyst, gave high yields, and offered wide functional group tolerance.

Enhancement of the Partial Oxidation of Methanol Reaction over CuZn Catalyst by Mn Promoter

A series of in situ experiments on mechanisms and top-down LHHW (Langmuir–Hinshelwood–Hougen–Watson) microkinetic analysis were conducted for the partial oxidation of methanol on CuMnZn (ca. 28.0 wt % Cu, 23 wt % Mn, and 49 wt % Zn) catalyst. In comparison with CuZn (ca. 29 wt % Cu and 71 wt % Zn), CuMnZn catalyst with the structure of copper–manganese spinel CuMn2O4 enhanced the turnover frequency (TOF) for methanol conversion at a lower temperature (from 4.2 to 10.1 s–1 at 150 °C). Mn also played a role in electronic charge transfer, which could enhance formate decomposition and mitigate the accumulation of carbonate species at high temperature. From a kinetic modeling analysis, the activation energy of CuZn-based catalyst was apparently reduced from 22.4 to 16.5 kcal/mol by the Mn promoter.

A novel non-selective coating material for solar thermal potential application formed by reaction between sol–gel titania and copper manganese spinel

A method for preparing a novel bixbyite non-selective coating for solar thermal conversion is described. The coating is formed by a thermal reaction between a titania sol–gel precursor with a copper manganese spinel to form a new material, Cu0.44Ti0.44Mn0.84Fe0.28O3, with a bixbyite structure. The effect of temperature and ratio between the two components on the formation of the bixbyite layer (deposited on Inconel by spray-coating) was studied. The absorptance of the films (AM 1.5; 335–2500 nm) with a thickness of 10±2 µm after annealing at 2 h at 650 °C and 750 °C was 97.4% and 94.7%, respectively. This synthesis represents a novel approach in which the final solar thermal coating is formed as a continuous and uniform layer which combines both the absorber and the ceramic binder. The developed material shows promising results for future applications as absorber in solar thermal energy conversion.

Reaction mechanisms of the copper–manganese spinel cathode in a solid oxide fuel cell

Cu 1.25Mn 1.75O 4 spinel (CMO) was studied as a potential solid oxide fuel cell (SOFC) cathode material at intermediate temperatures. The reaction mechanism of a composite cathode consisting of Cu 1.25Mn 1.75O 4 and yttria-stabilized zirconia (YSZ) was investigated by impedance spectroscopy. The influence of the CMO/YSZ ratio, time exposed to current passage and temperature on the impedance spectra was examined. Activation energy of the corresponding processes was calculated to be near 1 eV and between 1.32 and 1.96 eV for the high and low frequency arcs in the impedance spectra. Comparison between CMO-YSZ and Sr-doped LaMnO 3 (LSM)-YSZ composite cathodes showed they had similar reaction mechanisms. The transport or transfer of oxygen intermediates or oxide ions between the catalyst and electrolyte was suggested to be the rate determining steps between 700 and 800 °C, whereas dissociative adsorption, mass transfer and surface diffusion were rate controlling between 600 and 700 °C.

Solid oxide fuel cell composite cathodes prepared by infiltration of copper manganese spinel into porous yttria stabilized zirconia

Composite cathodes of Cu1.25Mn1.75O4 (CMO) spinel and yttria stabilized zirconia (YSZ) were made by infiltration of a precursor Cu–Mn gel into a porous YSZ matrix. Structural characterization showed no evidence of secondary phases but revealed a continuous network of CMO in the YSZ framework. Impedance spectroscopy and overpotential measurements revealed that the CMO–YSZ composite cathode had better electrochemical performance than the traditional LSM–YSZ cathode between 650 and 800 °C. A 50 wt% CMO impregnated YSZ cathode had a polarization resistance of 0.3 Ω cm2 at 750 °C, compared to 8.5 Ω cm2 for LSM–YSZ. Further investigation showed that charge transfer is the probable rate determining step for oxygen reduction in the CMO–YSZ cathode above 750 °C.

Waste-free Soft Reactive Grinding Synthesis of High-Surface-Area Copper–Manganese Spinel Oxide Catalysts Highly Effective for Methanol Steam Reforming

Cu–Mn spinel oxides with a high specific surface area were prepared by a simple and waste-free soft reactive grinding (SRG) technique involving the use of clean precursor salts as the starting materials. The samples were characterized by means of N2 adsorption, X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reduction (H2-TPR). The results show that the catalysts obtained from the SRG route exhibited much higher catalytic activity in methanol steam reforming as compared to their wet-chemically synthesized counterparts prepared by conventional coprecipitation. The superior performance of the SRG-derived Cu–Mn materials was attributed to the favorable formation of Cu1.5Mn1.5O4 spinel phase leading to the creation of much smaller copper nanoparticles with enhanced stability in the working catalyst.

Templated synthesis of high surface area inorganic oxides by silica aquagel-confined co-precipitation

A new and simple synthetic strategy for the preparation of high surface area nanosized metallic oxides using low cost precursors is described in this work. It is based on the coagulation – precipitation processes that occur when the metallic cations of salts dissolved in a silica aquagel medium are forced to precipitate by means of basic reagents. Nanoparticulate aggregates of the metallic oxides can then be obtained by applying the subsequent steps of drying, calcination and silica removal. Here, we illustrate the application of this technique by the preparation of both single and mixed metallic oxides such as copper oxide/ceria, hematite, cobalt ferrite and copper manganese spinel. The materials obtained in this way are made up by aggregates of nanosized particles (2–8 nm) and they exhibit very high surface areas up to 300 m 2/g. Depending on the chemical composition of the oxides, different structures ranging from quasi-rounded nanoparticles to aggregates of needle-shaped nanoparticles were obtained.

Electrical properties of copper–manganese spinel solutions and their cation valence and cation distribution

The cation valence and distribution in copper manganese spinels containing 1.0–1.6 mol copper per formula unit (Cu x Mn 3− x O 4) was resolved from their electrical conductivity and thermoelectric properties. The limit of thermal stability of the cubic spinel phase was also determined for each stoichiometry. A corrected phase diagram for the Cu–Mn–O system in air is proposed accordingly. The electronic defect structure could be described through a chemical approach, involving the competition between the redox of Cu + and Mn 4+ to Cu 2+ and Mn 3+ and the disproportionation of the Jahn–Teller ion Mn 3+ into Mn 2+ and Mn 4+. Thermodynamic parameters for the redox reaction were determined from experimental data as well as calculated, confirming the validity of the modeled defect equilibria.

In situ combustion synthesis of structured Cu-Ce-O and Cu-Mn-O catalysts for the production and purification of hydrogen

The combustion method was employed for the in situ synthesis of nanocrystalline Cu-Ce-O and Cu-Mn-O catalyst layers on Al metal foam, without the need of binder or additional calcination steps. Copper-manganese spinel oxides have been proposed as a catalytic system for hydrogen production via methanol steam reforming, while CuO-CeO2 catalysts have been successfully examined for CO removal from reformed fuels via selective oxidation. In this work, the performance of these catalysts supported on Al metal foam has been investigated in the reactions of methanol reforming and selective CO oxidation. The Cu-Ce-O foam catalyst exhibited similar catalytic performance to the one of the powder catalyst in the selective oxidation of CO. The performance of the Cu-Mn-O foam catalyst in the steam reforming of methanol was inferior to the one of the powder catalyst at intermediate conversion levels, but almost complete conversion of methanol was obtained at the same temperature with both foam and powder catalysts.

Steam reforming of methanol over copper–manganese spinel oxide catalysts

The steam reforming of methanol was studied over a series of copper–manganese spinel oxide catalysts prepared with the urea–nitrate combustion method. All catalysts showed high activity towards H 2 production with high selectivity. Synthesis parameters affected catalyst properties and, among the catalysts tested, the one prepared with 75% excess of urea and an atomic ratio Cu/(Cu + Mn) = 0.30 showed the highest activity. The results show that formation of the spinel Cu x Mn 3 − x O 4 phase in the oxidized catalysts is responsible for the high activity. Cu–Mn catalysts were found to be superior to CuO–CeO 2 catalysts prepared with the same technique.