Copper Manganite Research Articles

Copper-perovskite interfacial engineering to boost deNOx activity

By adjusting the Cu doping level and calcination temperature during synthesis of a series of noble metal-free lanthanum copper manganite perovskites LaCuxMn1-xO3, we show the importance of tuning the redox chemistry for optimum steering of the catalytic activity and N2 selectivity in the catalytic reduction of NO by CO. A prerequisite is the in situ formation of an extended copper-perovskite phase boundary. The associated improvement of redox and surface properties by Cu addition leads to an optimized balance of the reduction of the catalyst in the NO+CO reaction mixture. The creation of oxygen vacancies improves the reaction kinetics and initiates the NO dissociation. Strongly dependent on the calcination temperature, the Cu/Mn ratio, the reducing agent, as well as the reaction temperature as parameters for Cu-perovskite interfacial control, surface reduction can induce partial copper exsolution, significant perovskite reduction, agglomeration of exsolved Cu particles and eventual decomposition of the catalyst structure. We show that increasing the amount of initial copper incorporated into the perovskite structure can beneficially extend the phase boundary, but exceeding the amount of copper leads to increased sintering of the copper particles at the expense of catalyst activity, especially in repeated catalytic cycles. Increasing the calcination temperature, in addition to the initial sintering of the catalyst and shifting the reaction onset temperature to higher temperatures in the first cycle, improves the reduction resistance of the catalyst. Consequently, in order to form a higher amount of phase boundary-bound active sites, stronger reducing conditions than provided by the NO+CO reaction mixture are needed. This effect can be counterbalanced by using stronger reduction agents prior to performing subsequent catalytic cycles by inducing the exsolution process.

Room temperature thermocatalytic removal of formaldehyde in air using a copper manganite spinel-supported palladium catalyst with ultralow noble metal content

The room temperature (RT)-catalytic oxidation of gaseous formaldehyde (FA) in the dark is regarded as one of the most viable technical options for its removal from indoor air. Herein, the copper manganite spinel (CuMn2O4) supported palladium (Pd) catalysts are firstly synthesized for the thermocatalytic oxidation of FA in air. In particular, 0.05% Pd-CuMn2O4-R (‘R’ denotes high-temperature reduction pre-treatment using hydrogen) achieves 100% conversion (XFA) of 50 ppm FA at RT (gas hourly space velocity of 4342 h−1). The performance of 0.05% Pd-CuMn2O4-R against FA, if assessed in terms of the reaction kinetic rate (r at 10% XFA), is estimated as 3.01E−02 mmol g−1h−1. The lowering of XFA with the increases in FA concentration, flow rate, and relative humidity indicates the detrimental effects of such variables on the catalytic activity. FA oxidation kinetics predominantly follows the Mars van Krevelen mechanism. In-situ diffuse reflectance infrared Fourier transform spectroscopy shows that FA oxidation proceeds through multiple reaction intermediates (e.g., dioxymethylene and formate). The density functional theory simulations indicate that the catalytic oxidation efficacy of FA over CuMn2O4 increases by the synergy between Pd loading and surface reduction. The present study represents the first report on the synthesis of CuMn2O4-supported Pd catalysts and their application for the RT oxidative removal of FA in air under dark conditions. The findings of the present work offer valuable insights into the construction of efficient and cost-effective catalysts with ultra-low noble metal content for the RT oxidative removal of VOCs in indoor environment.

Low-temperature thermocatalytic removal of formaldehyde in air using copper manganite spinels

The removal of formaldehyde (FA) is vital for indoor air quality management in light of its carcinogenic propensity and adverse environmental impact. A series of copper manganite spinel structures (e.g., CuMn2O4) are prepared using the sol-gel combustion method and treated with reduction or oxidation pretreatment at 300 °C condition. Accordingly, CuMn2O4–O (“O” suffix for oxidation pre-treatment in air) is identified as the best performer to achieve 100% conversion (XFA) of FA (50 ppm) at 90 °C; its performance, if assessed in terms of reaction kinetic rate (r) at XFA = 10%, is 5.02E-03 mmol g−1 h−1. The FA removal performance increases systematically with decreases in flow rate, FA concentration, and relative humidity (RH) or with increases in bed mass. The reaction pathways and intermediates of FA catalytic oxidation on CuMn2O4-A are studied with density functional theory simulations, temperature-programmed characterization experiments, and in-situ diffuse reflectance infrared Fourier transform spectroscopy. The synergistic combination of large quantities of adsorbed oxygen (OA) species and oxidized metal species (e.g., Cu2+) contribute to the enhanced catalytic performance of CuMn2O4–O to oxidize FA into CO2 with the reaction intermediates of H2CO2 (DOM), HCOO−, and CO. The present study is expected to provide valuable insights into the thermocatalytic oxidation of FA over spinel CuMn2O4 materials and their catalytic performances in relation to the key process variables.

Alkali-modified copper manganite spinel for room temperature catalytic oxidation of formaldehyde in air

Formaldehyde (FA) is present ubiquitously in indoor environment as a hazardous pollutant with carcinogenic risks. For the efficient mitigation of FA, catalytic oxidation is a recommendable option to simultaneously satisfy both material cost (e.g., avoiding noble metals) and low-energy requirement (under dark and at room temperature (RT)). From this perspective, a cost-effective alkali modified copper manganite spinel (CuMn2O4) catalyst has firstly been prepared and employed for FA oxidation. Specifically, alkali (1 mol L−1 potassium hydroxide)-modified CuMn2O4 (1-CuMn2O4) achieves 100% FA (50 ppm (gas hourly space velocity of 4777 h−1)) conversion (XFA) at RT. The steady-state reaction rate of 1-CuMn2O4 at 10% XFA is 8.18 × 10−2 mmol g−1 h−1. According to in situ diffuse reflectance infrared Fourier transform spectroscopy, FA molecules are oxidized into water and carbon dioxide through dioxymethylene and formate intermediates. Based on density functional theory simulation, the higher catalytic performance of 1-CuMn2O4 for FA oxidation is attributed to the combined effects of firmer attachment of FA molecules to 1-CuMn2O4 surface, lower energy cost of FA adsorption, and lower desorption energy for the final products from the substrate surface. The present work is expected to provide insights into high-performing non-noble metal catalysts for RT oxidative removal of FA from indoor air.

Synthesis, characterization and investigation of hydrophobic and self-cleaning properties of modified Zn–Mn and Cu–Mn nano spinels

Nano spinels of zinc-manganite and copper-manganite were synthesized by the co-precipitation method. Characterization of synthesized nanoparticles has been carried out using X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV–vis diffuse reflectance spectroscopy (DRS), Field emission scanning electron microscopy (FESEM) and Atomic force microscopy (AFM) methods resulting in confirmation of the target phase formation performance of synthesized nanoparticles evaluated in photodegradation methyl red organic dye. In addition, synthesized nanoparticles were coated on sand-blasted glass and modified using palmitic acid to reach the hydrophobic surface. The contact angles of water droplets were measured for both surfaces which were 159° and 152° for zinc-manganite and copper manganite, respectively. The hydrophobicity of both coatings was available after 360 days making them a good candidate for the production of hydrophobic coating with photocatalytic activity in a blend with cement-like materials.

STUDY OF LOW-TEMPERATURE OXIDATION OF CARBON MONOOXIDE ON Cu–Mn–Fe CATALYTIC OXIDE SYSTEMS OBTAINED BY THE SOL-GEL COMBUSTION METHOD

The oxidation of carbon monoxide was studied on oxide Cu–Mn–Fe catalytic systems with metal ratio Cu:Mn:Fe=1:1:1; 2:1:1; 1:2:1 and 1:1:2 obtained by the sol-gel method with combustion. The results of X-ray phase analysis showed that the catalytic systems have a complex phase composition. Along with double oxides of manganese and iron, ferrites of copper-, manganese, copper manganite, manganese-substituted copper ferrites were formed (CuFe2O4; Mn0.43Fe2.57O4, Mn0.98Fe2.02O4; CuMn2O4; Cu1.2Mn1.8O4; Cu0.5Mn0.5Fe2O4). It has been found that depending on the ratio of metals in the catalyst, the reaction start temperature is in the temperature range of 120–1700C. And after 3–5 minutes after the start of the reaction, the conversion begins to increase sharply, reaching 100% within the next 5 minutes

Synthesis, structure and simulation of magnetic disorder of doped copper manganite La0.65Ce0.05Sr0.3Mn1−x Cu x O3

Synthesis, structure and simulation of magnetic disorder of doped copper manganite La_0.65Ce_0.05Sr_0.3Mn_1−<i>x</i>Cu_<i>x</i>O₃

Fabrication of Cu1.5Mn1.5O4 Nanoparticles Using One Step Self-Assembling Route to Enhance Energy Consumption

The preparation of copper manganite (hopcalite, Cu1.5Mn1.5O4), as a single phase, was achieved by using a sustainable method of green synthesis. This method is based on the replacement of the conventional “brute force” ceramic preparation by the recent “soft force” green synthesis via the egg white assisted one-step method. In other words, we present a facile and rapid methodology to prepare the nanocrystalline Cu1.5Mn1.5O4 spinel as a single phase, compared to our previous work using ceramic and glycine-assisted combustion methods. The as-synthesized copper manganite was characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), energy-dispersive spectroscopy (EDS), and scanning electron microscope (SEM). We used a vibrating sample magnetometer to determine the magnetic properties of the prepared sample (VSM). XRD, FTIR, SEM, EDS and transmittance electron micrograph (TEM) resulted in synthesis of a successful cubic spinel Cu1.5Mn1.5O4 system with a sponge crystal structure. The particles of the prepared materials are polycrystalline in their nature and the sizes ranged between 50 and 100 nm. The magnetic measurement demonstrated that the generated nanostructure has been found to exhibit ferromagnetism at room temperature with an optimum saturation magnetization value (0.2944 emu/g).

Temperature-Limited Synthesis of Copper Manganites along the Borderline of the Amorphous/Crystalline State and Their Catalytic Activity in CO Oxidation.

Copper manganese oxides (CMO) with CuMn2O4 composition are well-known catalysts, which are widely used for the oxidative removal of dangerous chemicals, e.g., enhancing the CO to CO2 conversion. Their catalytic activity is the highest, close to those of the pre-crystalline and amorphous states. Here we show an easy way to prepare a stable CMO material at the borderline of the amorphous and crystalline state (BAC-CMO) at low temperatures (<100 °C) followed annealing at 300 °C and point out its excellent catalytic activity in CO oxidation reactions. We demonstrate that the temperature-controlled decomposition of [Cu(NH3)4](MnO4)2 in CHCl3 and CCl4 at 61 and 77 °C, respectively, gives rise to the formation of amorphous CMO and NH4NO3, which greatly influences the composition as well as the Cu valence state of the annealed CMOs. Washing with water and annealing at 300 °C result in a BAC-CMO material, whereas the direct annealing of the as-prepared product at 300 °C gives rise to crystalline CuMn2O4 (sCMO, 15–40 nm) and ((Cu,Mn)2O3, bCMO, 35–40 nm) mixture. The annealing temperature influences both the quantity and crystallite size of sCMO and bCMO products. In 0.5% CO/0.5% O2/He mixture the best CO to CO2 conversion rates were achieved at 200 °C with the BAC-CMO sample (0.011 mol CO2/(m2 h)) prepared in CCl4. The activity of this BAC-CMO at 125 °C decreases to half of its original value within 3 h and this activity is almost unchanged during another 20 h. The BAC-CMO catalyst can be regenerated without any loss in its catalytic activity, which provides the possibility for its long-term industrial application.

Synthesis and Characterisation of Structural and Electrical Properties of CuMn2O4 Spinel Compound

CuMn2O4 was synthesized by the solid-state method. MnO2 and CuO were used as precursors. The optimum temperature of synthesis was 850°C. XRD results showed that the prepared compound had a cubic structure with Fd3 ̅m space group. The lattice constant and unit cell volume were a=8.359Å and V=584.14A°3 respectively. The grain size was calculated by the Debye-Scherrer method and was 33.49 nm for CuMn2O4 annealed at 850°C. The experimental density was calculated and compared to the theoretical density. The results were ρt= 5.399 gr/cm3 and ρE = 5.24 gr/cm3. The electrical properties of the compound showed that it behaves like a semiconductor, and the activation energy of the compound was 0.1535 eV. KEYWORDS Activation energy, copper manganite (CuMO), mixed oxide, solid-state reaction, spinel

Studies on structural and optical behavior of SnO2/CuMn2O4 nanocomposite developed via two-step approach for photocatalytic activity

In this current work, tin oxide (SnO2)/copper manganite (CuMn2O4) nanocomposite (NCs) were developed form the two step process. In this process, CuMn2O4 NPs were prepared by co precipitation approach and subsequently SnO2/CuMn2O4 NCs were synthesized via hydrothermal method. The crystalline phase structures of CuMn2O4 (face centered cubic) and SnO2 (tetragonal rutile structure) were reveals from the Power x-ray Diffraction (PXRD) pattern. The observed various range of functional groups in the CuMn2O4 and SnO2/CuMn2O4 NCs were investigated by Fourier transform infrared spectroscopy (FTIR) studies. The surface morphology of the prepared material was primarily examined by Scanning Electron Microscopy (SEM) analysis and presence of elemental composition from the prepared material was investigated by the EDAX analysis. The photocatalytic performance of the prepared SnO2/CuMn2O4 NCs was evaluated from the organic dyes of Methylene Blue (MB) and Malachite Green (MG). The dye degradation efficiency of the prepared catalyst was achieved to be 90% and 88% against MG and MB dyes under sun light irradiation. These superior photocatalytic activity exhibits that the prepared SnO2/CuMn2O4 NCs is a potential candidate for waste water treatment.

Flake-like CuMn2O4 nanoparticles synthesized via co-precipitation method for photocatalytic activity

In present work, flake-like CuMn2O4 (Copper manganite) Nanoparticles (NPs) were prepared by Co-precipitation method. The FCC spinel phase structure was determined from the PXRD pattern. The optical properties were analyzed by UV–Vis DRS spectroscopy and energy band gap is found to be 2.54 eV. From the FTIR analysis, two bands are observed at 605 cm−1and 498 cm−1 respectively for metal oxide bonds of Cu–O and Mn–O which is originating from the stretching vibration modes. From the SEM analysis, the size of the prepared material was found to be 50–100 nm. The EDAX spectrum reveals that there are no impurities were present in the CuMn2O4 NPs. Towards the application perspective, the photocatalytic performance was examined by the prepared CuMn2O4 NPs against the organic dyes of Methylene Blue (MB) and Malachite Green (MG) and their corresponding degradation efficiencies are 86% and 92% under sunlight irradiation.

Composites of Laponite and Cu–Mn Hopcalite-Related Mixed Oxides Prepared from Inverse Microemulsions as Catalysts for Total Oxidation of Toluene

Composites of Laponite and Cu–Mn hopcalite-related mixed oxides, prepared from hydrotalcite-like (Htlc) precursors obtained in inverse microemulsions, were synthesized and characterized with XRF, XRD, SEM, TEM, H2 temperature-programmed reduction (TPR), and N2 adsorption/desorption at −196 °C. The Htlc precursors were precipitated either with NaOH or tetrabutylammonium hydroxide (TBAOH). Al was used as an element facilitating Htlc structure formation, and Ce and/or Zr were added as promoters. The composites calcined at 600 °C are mesoporous structures with similar textural characteristics. The copper–manganite spinel phases formed from the TBAOH-precipitated precursors are less crystalline and more susceptible to reduction than the counterparts obtained from the precursors synthesized with NaOH. The Cu–Mn-based composites are active in the combustion of toluene, and their performance improves further upon the addition of promoters in the following order: Ce < Zr < Zr + Ce. The composites whose active phases are prepared with TBAOH are more active than their counterparts obtained with the use of the precursors precipitated with NaOH, due to the better reducibility of the less crystalline mixed oxide active phase.

Transition Metal Manganites Prepared by a Green and Low-Temperature Wet Chemistry Route, Investigated by XPS

In the present contribution, three transition metal manganites, namely the copper manganite CuMnO2 and the zinc manganites ZnMnO3 and ZnMn2O4, were investigated through X-ray photoelectron spectroscopy (XPS). The chosen synthesis route involved the combination of coprecipitation of oxalates from an aqueous solution and hydrothermal processing at a mild temperature (180 °C). The precipitates were then separated and dried for 4 h at 80 °C, yielding crystalline nanostructured powders without the need for calcination. Along with survey scans of the analyzed samples, detailed spectra of the C 1s, O1s, Mn 2p, Mn 3p, Mn LMM as well as Cu 2p, Cu 3p, Cu LMM, Zn 2p and Zn LMM (depending on the sample in question) were collected. The data obtained from these analyses is discussed.

MOD법으로 제조된 Copper Manganite 박막의 구조 및 NTCR 특성

Copper manganite thin films were fabricated on <TEX>$SiN_x/Si$</TEX> substrate by metal organic decomposition (MOD) process. They were burned-out at <TEX>$400^{\circ}C$</TEX> and annealed at various temperatures (<TEX>$400{\sim}800^{\circ}C$</TEX>) for 1h in ambient atmosphere. Their micro-structure and negative temperature coefficient of resistance (NTCR) characteristics were analyzed for micro-bolometer application. The copper manganite film with a cubic spinel structure was well developed at <TEX>$500^{\circ}C$</TEX> which confirmed by XRD and HRTEM analysis. It showed a low resistivity (<TEX>$47.5{\Omega}{\cdot}cm$</TEX>) at room temperature and high NTCR characteristics of <TEX>$-4.12%/^{\circ}C$</TEX> and <TEX>$-2.15%/^{\circ}C$</TEX> at room temperature and <TEX>$85^{\circ}C$</TEX>, implying a good thin film for micro-bolometer application. Furthermore, its crystallinity was enhanced with increasing temperature to <TEX>$600^{\circ}C$</TEX>. However, the appearance of secondary phase at temperatures higher than <TEX>$600^{\circ}C$</TEX> lead to deteriorate the NTCR characteristics.

OXYGEN REDUCTION ON Cu1 ,Mn16O4 SPINEL PARTICLES COMPOSITE ELECTRODES EFFECT OF PARTICLES SIZE

ABSTRACT The oxygen reduction reaction (orr) was studied on CG/PPy/PPy(Ox)/PPy and CG/paint/CC(Ox)PPy composite electrodes, CG representing conducting glass, PPy polypyrrole, CC carbon cloth and Ox mixed valence spinel oxide particles of transition metals Cu 1.4 Mn 1.6 O 4 in 0.2 M KCl pH = 9.2, at room temperature. PPy is electrochemically polymerized and serves as a protective layer to dispersed oxide particles in the carbon cloth. Oxide particles size varied from 7.6 to 11.2 µm. The orr takes place on the oxide particles with formation of hydrogen peroxide which diffuses to electrolyte solution. The amount of peroxide ions produced was detected using the rotating ring-disk electrode technique and determined indirectly by iodine spectroscopy. The peroxide ions production depends strongly on the oxide particle size. Keywords: Copper manganites, Spinel oxide, Composite electrode, Polypyrrole, Oxygen electroreduction. INTRODUCTION The importance of the cathodic oxygen reduction reaction (orr) to water either directly or indirectly via hydrogen peroxide is widely recognized due to their applications such as oxygen electrode in fuel cells, lithium-air batteries, wastewater treatments and, organic and inorganic synthesis. In fuel cells the orr is the only employed reaction to accept electrons from chemicals such as methanol, ethanol or other molecules

Magnetic, oxidation and reduction behavior of spinel Ni–Cu manganite Ni x Cu 1-x Mn 2 O 4 powders

Abstract Nickel copper manganites, Ni x Cu 1-x Mn 2 O 4 (where 0 ≤ X ≤ 1), powders have been synthesized via co-precipitation method. The formed particles were obtained from the precipitate precursors annealed at 800 °C for 2 h. The prepared powders were tested for the catalytic oxidation of carbon monoxide (CO) into carbon dioxide (CO 2 ). The results indicated that the intermediate compositions displayed better catalytic activity than the end compositions for CO oxidation due to the phenomena of synergism. The composition of x = 0.3 and 0.5 showed rapid rise in CO conversion with temperature; about 40% conversion was achieved at 200 °C for the produced manganite sample of chemical composition Cu 0 . 7 Ni 0 . 3 Mn 2 O 4 . A correlation between magnetic properties and hydrogen reduction of manganites was demonstrated. Magnetic properties of reduced manganite were found to be duplicated. The saturation magnetization of reduced NiMn 2 O 4 into Ni/MnO was duplicated of order 15 times from initial value.

Effect of Li2O – Doping on physicochemical, surface and catalytic properties of nanosized CuO–Mn2O3/cordierite system

Physicochemical, surface and catalytic properties of pure and Li2O-doped (0.75–3.0 mol%) CuO–Mn2O3 supported on cordierite (commercial grade) preheated in air at 500 °C were investigated using XRD, EDX, nitrogen adsorption at −196 °C and catalysis of CO-oxidation by O2 at 250 °C. The results revealed that treating the support material with 10 wt% of both CuO and Mn2O3 followed by heating in air at 500 °C which much increased its SBET (several folds) led to the formation of nanosized CuO and CuMn2O4 phases. Li2O-doping enhanced copper manganite (CuMn2O4) formation. The doping process increased effectively the surface concentration of both copper and manganese species due to an enhanced formation of CuMn2O4 on top surface layers of the doped system leading to an important increase in its catalytic activity.

New synthesis of nanosized Cu–Mn spinels as efficient oxidation catalysts

Copper manganese nanoscale oxides were prepared using a novel method with low cost natural biopolymer precursor, alginate, and their catalytic activity was evaluated for the complete oxidation of toluene as a model VOC. Depending on the Cu/Mn ratio the following oxides were formed: Mn3O4, Cu1.5Mn1.5O4, CuO or a mixture of these phases, as detected by XRD. The nanocrystals aggregate in small spheres (≲1mm), which retain the shape of the parent gel and present homogeneous composition as characterized by TEM and SEM-EDX. The best performance for toluene combustion was observed for the cubic spinel Cu1.5Mn1.5O4 nanoparticles (∼10nm), which was able to completely oxidize toluene at ∼240°C. For the pure oxides the activity order: Cu1.5Mn1.5O4>Mn3O4>CuO, correlates with the TPR results as the catalyst with the higher redox potential shows higher activity. For comparison the TiO2 supported oxides were also studied and alginate issued Cu1.5Mn1.5O4 mixed with TiO2 presented similar activity as the Cu–Mn oxide deposited on TiO2 by incipient wetness impregnation however the overall activity of supported oxides was lower than for the unsupported Cu1.5Mn1.5O4. The method used for the synthesis of copper manganite has great potential as it can be extended to other manganite spinels of general formula AMn2O4 and presents the advantage of easy catalyst forming.

Studies on the properties of Ni0.6Cu0.4Mn2O4 NTC ceramic due to Fe doping

The influence of the Fe on the microstructure, electrical and dielectric properties of Ni0.6Cu0.4FeyMn2−yO4 (0.1≤y≤0.5) negative temperature coefficient (NTC) thermistors prepared by well known simple chemical co-precipitation method were studied. The replacement of manganese by iron plays an important role in changing the lattice parameter, X-ray density, sintered density, porosity, DC resistivity at different temperatures and dielectric properties at different frequencies. The X-ray and sintered density increased linearly and porosity decreased with iron. The room temperature resistivity of nickel copper manganite NTC ceramic decreased from 1MΩcm to 68KΩcm and dielectric constant increased from ∼9×107 to 1.5×109 at 20Hz as iron content increased.