CuFe2O4 Spinel Research Articles

Stability of CuZnOAl2O3/HZSM-5 and CuFe2O4/HZSM-5 catalysts in dimethyl ether steam reforming operating in reaction–regeneration cycles

The study focuses on the regenerability of bifunctional catalysts prepared with different metallic functions (CuZnOAl2O3 and CuFe2O4 spinel) and HZSM-5 zeolite (SiO2/Al2O3=30) as the acid function. These catalysts have been employed for H2 production in the steam reforming of dimethyl ether in a fluidized bed reactor, operating in reaction-regeneration cycles. The regeneration of the catalysts was carried out by combustion in air (at 315 or 500°C) of the deposited coke, in order to establish: i) the coke combustion temperature required for recovering the activity of the metallic and acid functions; and ii) the kinetic behavior of the catalysts after removing the coke deposited on the metallic function and after the complete removal of coke. At 315°C only the coke deposited on the metallic sites is burned, whereas 500°C is required to remove the coke deposited on the zeolite. The catalyst with CuFe2O4 spinel metallic function exhibits higher stability and allows operating uninterruptedly under reaction–regeneration cycles, since it recovers its activity after regeneration at 500°C. The catalyst with CuZnOAl2O3 metallic function, which is more active than the Cu-Fe spinel for the dymethyl ether steam reforming, deactivates irreversibly at 500°C due to Cu sintering.

Copper ferrites: A model for investigating the role of copper in the dynamic iron-based Fischer–Tropsch catalyst

Copper is a well-known reduction promoter for Fe-based Fischer–Tropsch catalysts. The role of copper is investigated using spinel copper ferrite, CuFe2O4, and delafossite, CuFeO2, as model compounds and compared with hematite. The incorporation of copper within the crystal structure results in a facile, initial reductive decomposition of the structure into magnetite and metallic copper during the catalyst pre-treatment in either hydrogen or carbon monoxide. Copper facilitates the consecutive conversion of magnetite to α-Fe in hydrogen, but not its conversion to predominantly χ-Fe5C2 in CO. The amount of carbide in the catalyst under Fischer–Tropsch conditions is dependent on the presence of copper in close proximity to the iron phases. The observed increase in catalytic activity in the catalysts ex copper ferrites is primarily due to the increased carbide surface area within the catalyst. The copper-containing model compounds show a higher CO2-selectivity, which is ascribed to the presence of a larger amount of small magnetite crystallites present during the Fischer–Tropsch synthesis. Furthermore, copper seems to facilitate secondary olefin hydrogenation.

Reduction behaviors and catalytic properties for methanol steam reforming of Cu-based spinel compounds CuX2O4 (X=Fe, Mn, Al, La)

In this study, various Cu-based spinel compounds, i.e., CuFe2O4, CuMn2O4, CuAl2O4 and CuLa2O4, were fabricated by a solid-state reaction method. Reduction behaviors and morphological changes of these materials have been characterized by H2 temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Moreover, the catalytic properties for steam reforming of methanol (SRM) of these Cu-based spinel compounds were investigated. H2-TPR results indicated that the reducibility of Cu-based spinel compounds was strongly dependent on the B-site component while the CuFe2O4 catalyst revealed the lowest reduction temperature (190°C), followed respectively by CuAl2O4 (267°C), CuMn2O4 (270°C), and CuLa2O4 (326°C). The reduced CuAl2O4 catalyst demonstrated the best performance in terms of catalytic activity. Based on the SEM and XRD results, pulverization of the CuAl2O4 particles due to gas evolution and a high concentration of nanosized Cu particles (≈50.9nm) precipitated on the surfaces of the Al2O3 support were observed after reduction at 360°C in H2. The BET surface area of the CuAl2O4 catalyst escalated from 5.5 to 13.2m2/g. Reduction of Cu-based spinel ferrites appear to be a potential synthesis route for preparing a catalyst with high catalytic activity and thermal stability. The catalytic performance of these copper-oxide composites was superior to those of conventional copper catalysts.

Liquefied petroleum gas sensing performance of cerium doped copper ferrite

Undoped and cerium (Ce) doped nanocrystalline copper ferrite (CuFe2O4) materials were synthesized via the molten-salt (M-S) method. Effects of Ce doping on the structural, morphological and gas sensing properties of the CuFe2O4 ferrite have been investigated. X-ray diffraction (XRD) analysis revealed the formation of spinel CuFe2O4. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations showed that the synthesized ferrite is made up of very fine spherical nanoparticles. Moreover, the gas sensing properties of sintered samples were studied towards different reducing gases such as liquefied petroleum gas (LPG), acetone, ethanol and ammonia. The sample with 4% cerium doped CuFe2O4 (Ce4) showed the maximum gas sensitivity (86%) towards LPG with fast response time of 5 s and good recovery time of 68 s.

Investigation on effects of surface morphologies on response of LPG sensor based on nanostructured copper ferrite system

Synthesis of a copper ferrite system (CuFe2O4) via chemical co-precipitation method is characterized by X-ray diffraction, surface morphology (scanning electron microscope) and optical absorption spectroscopy. These characteristics show their dependence on the relative compositions of the two subsystems. They are further confirmed by the variation in the band gap.A study of gas sensing properties shows the spinel CuFe2O4 synthesized in 1:1 molar ratio exhibit best response to LPG adsorption/resistance measurement. Thus resistance based LPG sensor is found robust, cheap and may be applied for kitchens and industrial applications.

Cu-Fe Spinel Coating as Oxidation Barrier for Fe-16Cr Metallic Interconnect in Solid Oxide Fuel Cells

A conductive spinel CuFe2O4 is used to protect the metallic interconnect of solid oxide fuel cells (SOFCs) from oxidation and prevent the cathode from chromium poisoning. It is coated by the sol-gel method on a typical metallic interconnect material of Fe-16Cr alloy and evaluated by oxidation at 800°C for 200 h in air (the cathode atmosphere) under an applied current of 0.5 A cm−2. The results show that the coating is promising in providing oxidation resistance, and the oxide scale formed on both the positive and negative sides of the substrate are similar, which consists of a thin inner layer of Cr2O3, a middle layer of Cu-doped MnCr2O4 and a top layer of Fe2O3 with an overall thickness around 2 μm and grows less than 0.5 μm during the 200 h oxidation. The extrapolated area specific resistance (ASR) of the oxide scale at 800°C is approximately one seventh that formed on the uncoated Fe-16Cr alloy, suggesting that the outward migration of cations from the alloy substrate to the oxide scale is driven by the gradient of chemical potential rather than that of electrical potential in this particular situation due to the relatively high scale conductivity.

Preparation, structure and catalytic properties of magnetically separable Cu–Fe catalysts for glycerol hydrogenolysis

The Cu–Fe catalysts with stoichiometric proportion (Cu/Fe molar ratio was 0.5) were prepared by an epoxide assisted route. The structural properties of Cu–Fe catalysts were determined by X-ray diffraction (XRD), and Mossbauer spectroscopy measurements. These results indicated that a crystalline phase transformation from c-CuFe2O4 to t-CuFe2O4 occurred when elevating the calcination temperature from 500 to 600 °C. The M–H plots exhibited that all Cu–Fe catalysts had ferromagnetic nature and the saturation magnetization values monotonously increased with increasing calcination temperature irrespective of the phases composition. The significant superparamagnetic behavior was observed in the results of magnetic and Mossbauer spectroscopy measurements. The H2 temperature-programmed reduction (H2-TPR) was also conducted for examining the reducibility of Cu–Fe catalysts. The catalytic performance of Cu–Fe catalysts was examined for the hydrogenolysis reaction of glycerol. It is found that the formation of spinel CuFe2O4 greatly enhances the hydrogenolysis activity. The highest glycerol conversion (47%) was obtained over CuFe-500 catalyst, while the selectivity of 1,2-propanediol was maintained at about 92% for all catalysts.

Magnetic properties of nanocrystalline CuFe2O4 and kinetics of thermal decomposition of precursor

CuFe2(C2O4)3·4.5H2O was synthesized by solid-state reaction at low heat using CuSO4·5H2O, FeSO4·7H2O, and Na2C2O4 as raw materials. The spinel CuFe2O4 was obtained via calcining CuFe2(C2O4)3·4.5H2O above 400 °C in air. The CuFe2(C2O4)3·4.5H2O and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform FT-IR, X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer, and vibrating sample magnetometer. The result showed that CuFe2O4 obtained at 400 °C had a saturation magnetization of 33.5 emu g−1. The thermal process of CuFe2(C2O4)3·4.5H2O experienced three steps, which involved the dehydration of four and a half crystal water molecules at first, then decomposition of CuFe2(C2O4)3 into CuFe2O4 in air, and at last crystallization of CuFe2O4. Based on KAS equation, OFW equation, and their iterative equations, the values of the activation energy for the thermal process of CuFe2(C2O4)3·4.5H2O were determined to be 85 ± 23 and 107 ± 7 kJ mol−1 for the first and second thermal process steps, respectively. Dehydration of CuFe2(C2O4)3·4.5H2O is multistep reaction mechanisms. Decomposition of CuFe2(C2O4)3 into CuFe2O4 could be simple reaction mechanism, probable mechanism function integral form of thermal decomposition of CuFe2(C2O4)3 is determined to be 1 − (1 − α)1/4.

Synthesis, structural and magnetic characterization of nanocrystalline CuFe2O4 as obtained by a combined method reactive milling, heat treatment and ball milling

Nanocrystalline copper ferrite has been synthesized using a combined method which involves reactive milling, heat treatment and mechanical milling. After 4h of reactive milling a solid solution between the starting oxides (CuO and α-Fe2O3) and a spinel phase is obtained. Increasing the milling time leads to a decomposition of those phases. After a heat treatment of the 30h milled sample a single spinel CuFe2O4 phase is obtained. By mechanical milling the crystallite size of the copper ferrite is reduced down to 9nm after 1h of milling. For the CuFe2O4 samples milled between 2 and 4h a decomposition of this phase is remarked and α-Fe2O3 is formed during milling. The spontaneous magnetization of the spinel decreases with increasing the milling time as results of the partial redistribution of the cations in the spinel and of spin canted effect. The magnetization of the milled samples does not saturate due to the presence of very fine ferrite particles which are superparamagnetic.

Self-assembled porous nano-composite with high catalytic performance by reduction of tetragonal spinel CuFe2O4

Abstract A tetragonal spinel CuFe 2 O 4 reduced in H 2 flow at 633 K shows a self-assembled microstructure that exhibits fine dispersion of copper nanoparticles within the porous Fe 3 O 4 matrix and high catalytic performance. Sintering of copper particles was inhibited significantly even after H 2 reduction at 873 K when CuFe 2 O 4 was used as a precursor, while it readily occurred for CuO and physically mixed CuO + Fe 2 O 3 . The high thermal stability of copper nanoparticles from the CuFe 2 O 4 after H 2 reduction is ascribed to the immiscible interaction between copper and iron (or iron oxides). The spinel CuFe 2 O 4 can be regenerated after an intentional sintering treatment (e.g., in H 2 at 873 K) by calcinations in air at 1273 K where the activity and the morphology restored completely. We show that metallurgical knowledge is available to tailor microstructure for designing catalysts.

Crystal structure and surface species of CuFe2O4 spinel catalysts in steam reforming of dimethyl ether

Copper–iron spinel (CuFe2O4) in cubic phase was prepared via a simple citrate sol–gel method, and was transformed into tetragonal phase of high crystallinity by calcining in air at 900°C. Composites of CuFe2O4 spinel and γ-Al2O3 were investigated for catalytic production of hydrogen from dimethyl ether steam reforming (DME SR). X-ray photoelectron spectroscopy showed Cu1+-rich surface species (Cu1+/Cu0=ca. 3/2 with negligible Cu2+) over the calcined CuFe2O4 subjected to in situ H2 reduction. The spinel-oxides with lower content of reducible Cu species possessed higher amount of Cu1+ species under the reducing atmosphere, corresponding to higher DME SR activity. Copper clusters highly dispersed in the matrix of iron oxides were reduced from the spinel structure, and the strong interaction between them should result in the high activity and durability. The degraded catalysts after DME SR were regenerated by calcining in air in the temperature range of 350–800°C. Slow deactivation of the composites observed during DME SR at 375°C was mainly attributable to non-graphitic carbonaceous species deposited on the catalyst surface.

X-ray photoelectron spectroscopy characterization of copper–iron spinel as a catalyst for steam reforming of oxygenated hydrocarbon

Well-crystallized spinel CuFe2O4 in the tetragonal phase is obtained by calcination at 900 °C of the cubic CuFe2O4 prepared via a citrate sol–gel method. X-ray photoelectron spectroscopy coupled with Auger electron spectroscopy analysis reveals a high Cu1+/Cu0 ratio of ∼3/2 with negligible Cu2+ over the calcined CuFe2O4 subjected to in situ H2 reduction. The Cu1+-rich surface is considered to play a key role on the excellent catalytic performance in steam reforming of dimethyl ether for hydrogen generation.

Spinel CuFe2O4: a precursor for copper catalyst with high thermal stability and activity

Spinel CuFe2O4 has been studied as a precursor for copper catalyst. The spinel CuFe2O4 was effectively formed on the SiO2 by calcination in air at 800 °C with the atomic ratio of Fe/Cu = 2. The spinel CuFe2O4 on the SiO2 was reduced to fine dispersion of Cu and Fe3O4 particles by the H2 reduction at 240 °C. After H2 reduction at 600 °C, sintering of Cu particles over the CuFe2O4/SiO2 (Fe/Cu = 2) was inhibited significantly, while fatal sintering of Cu particles over the Cu/SiO2 (Fe/Cu = 0) occurred. The CuFe2O4/SiO2 catalyst exhibited much higher activity and thermal stability for steam reforming of methanol (SRM), compared with the Cu/SiO2 catalyst. The spinel CuFe2O4 on the SiO2 can be regenerated after an intentional sintering treatment by calcination in air at 800 °C where the activity is also restored completely. Based on these findings, we propose that spinel CuFe2O4 is an effective precursor for a high performance copper catalyst in which the immiscible interaction between Cu and Fe (or Fe oxide) plays an important role in the stabilization of Cu particles.

除菌効果を示す超微粒子フェライトの諸性質

A bacterial removing effect of ultrafine ferrite particles prepared by chemical coprecipitation has been investigated. The ten kinds of ferrite nanoparticles were tested, and CdFe2O4, CuFe2O4, ZnFe2O4, Ca0.5Zn0.5Fe2O4 and Ni0.5Zn0.5Fe2O4 showed the effects to reduce bacterial titers of L. pneumophila, S. aureus, P. aeruginosa, B. subtilis and E. cob. in the liquid culture. The crystal structure of ZnFe2O4, Ca0.5Zn0.5Fe2O4 and Ni0.5Zn0.5Fe2O4 analized by XRD method was the spinel structure, while CdFe2O4 and CuFe2O4 are composed of the spinel structure and small amounts of byproducts. These ferrite particles shared common physical properties, ie, average size of ferrite particles with bacterial removing effects was uniformly less than 15 nm, specific surface area was more than 140m2/g, saturation magnetization was less than 0.35 T and coercivity was less than 6.4kA/m.