Spinel-type Oxides Research Articles

High temperature corrosion and wear behavior of HVOF-sprayed coating of Al2O3-NiAl on AISI 304 stainless steel

High velocity oxy-fuel (HVOF) technique was used to deposit an Al2O3-30(Ni20Al) coating on AISI 304 stainless steel substrate to improve its corrosion and wear performance at high temperature. First, thermal cycling tests at 750 and 850 °C were conducted in air atmosphere on both coated and uncoated stainless steel substrates to study the effectiveness of coating protection system at different exposure times (2, 6, 10 and 15 days). Then, high temperature corrosion and wear mechanisms were studied by SEM and XRD techniques. These analyses revealed that uncoated specimens were severely corroded but no oxidation on the coated substrates was detected. Oxide growth on the uncoated substrate was mainly formed by spinel (MnCr2O4 and FeCr2O4) and corundum (Fe2O3 and Cr2O3) type oxides. Meanwhile, these oxides were not found on the coated substrate. Wear rate of the coated specimen was found to be reduced from 6.9·10−4 to 8.3·10−5 mm3/N·m compared to that of the uncoated specimen. The exposure to high temperatures improved coating wear resistance: wear rate was four times lower in the coated sample exposed to high temperatures compared to that of the non-exposed coated sample due to the formation of a harder phase of NiO.

Hydrothermal Approach to Spinel-Type 2D Metal Oxide Nanosheets.

The peculiar physical and chemical properties of 2D nanostructures have aroused global research interest in developing new members, synthetic technology, and exploring their potential applications in functional nanodevices. However, it is extremely challenging to directly obtain the 2D nanosheets for these extrinsic layered structures using conventional routines. In this work, we demonstrate the facile and general synthesis of 2D spinel-type metal oxides nanosheets through a simple hydrothermal reaction. Using this method, cubic γ-Ga2O3, ZnGa2O4 and MnGa2O4 nanosheets with triangular/hexagonal configuration and ultrathin thickness have been synthesized, and all these nanosheets show preferential growth along (111) plane with the minimum formation energy. Microstructural and composition analyses using HRTEM, EDS, XPS, and so on reveal that the as-synthesized 2D nanosheets are well-crystallized in cubic fcc-phase and show high purity in composition, and the formation process of MGa2O4 nanosheets can be regarded as the competition of M2+ and Ga3+ in tetrahedral site. Spatially resolved cathodoluminescence measurement of individual 2D nanosheet shows that the γ-Ga2O3, ZnGa2O4, and MnGa2O4 nanosheets exhibit distinct luminescence behavior, and ZnGa2O4 nanosheets show the strongest emission in visible region. It is expected that the facile synthesis of spinel-type metal oxides of γ-Ga2O3, ZnGa2O4, and MnGa2O4 nanosheets will further promote the exploration of a variety of semiconductor nanostructures that could not be achieved using conventional technology suitable for layered structures and will also open up some opportunities for the integration of advanced functional nanodevices such as photodetectors, phosphors on the basis of them.

Solid State Synthesis of Spinel-Type Metal Oxide Mg1.5Fe0.5MnO4 and Study of Its Exchange Capability for Li+

The spinel-type composite metal oxide, magnesium-manganese-titanium oxide (Mg1.5Fe0.5MnO4), was prepared by the method of solid state crystallization. As a spinel-type structure, it is versatile in chemical composition and its stoichiometric number. It could keep crystal structure stability by changing stoichiometric number method to insert or extract some substitutable ions. This characteristic can be special studied to meet some requirements. This spinel-type composite metal oxide was detected by XRD and SEM for the valuating partition coefficient of saturated exchange capacity and the other parameters to confirm certain characteristics. The dissolution rate of Fe2+ and Mn4+ from Mg1.5Fe0.5MnO4 which was treated by acid were less than 9.3%, meanwhile the extraction rate of Mg2+ was more than 75%. The experimental data showed that the acidifying of MgFeMn-620 (H) can reach 12.1 mmol g–1 ion exchange capacity for Li+ in solution.

A lithium selective adsorption composite by coating adsorbent on PVC plate using epoxy-silica hybrid binder

The industrial demand for lithium especially in a battery is expected to be high in near future. The use of lithium selective adsorbents, such as spinel-type lithium manganese oxides (LMOs) show the potential candidates for recovery of lithium from seawater. Here we report the approach for recovery of lithium from seawater using a new composite composed of LMO and epoxy-silica hybrid binder (HB) prepared by sol-gel method. The LMO and HB composites were coated on polyvinyl chloride (PVC) plate and its adsorption efficiency was studied in terms of binder contents and thickness. The composite showed excellent physicochemical and mechanical durability in seawater. The adsorption capacity of 6.5 mg/g (67% in comparison to that by powder LMO) was obtained in natural seawater when the composition of HB/LMO was 30/70 (in dry wt%) at a thickness of 300 μm. The kinetic study showed that the lithium adsorption on composite obtained using 30 mg/L Li spiked seawater was found to be matched to pseudo-second order model as the coating thickness was <230 μm, and turned to follow intra particle model over 230 μm due to diffusion limit of lithium ion into the inside of coated adsorbent. The results displayed good reproducibility over 5 consecutive adsorption/desorption cycles without significant efficiency drop. The results suggest that the composite tested in this study has good feasibility in practical application to seawater on large scale.

One-step synthesis and deposition of ZnFe2O4 related composite films via SPPS route for photodegradation application

Binary spinel-type metal oxides (AB2O4) related materials, including ferrites (AFe2O4), are attractive photocatalysts thanks to their excellent visible light response for the photodegradation of organic pollutants. Currently, these materials are synthesized via conventional chemical routes suffering from long preparation duration and multistep. Moreover, the photocatalysts are obtained as nano-powders from conventional chemical routes would introduce another drawback for their recycling and reuse. From an industrial perspective, it is desirable to develop an efficient and facile synthesis process to produce photocatalysts in a non-dispersible form. Herein, we demonstrate that the solution precursor plasma spray (SPPS) process is a single-step method for depositing photocatalytically active zinc ferrite-based films within several minutes. The influence of the precursor ratio on the microstructures and phase compositions of the ZnFe2O4 films was investigated by XRD and Raman analyses. In addition, two optimized ZnFe2O4 films were prepared by increasing the ZnO loading and tailoring injection pattern of the precursor solution. The surface morphologies and optical bandgap were also determined by SEM and UV–visible spectroscopy. The photocatalytic activities of the ZnFe2O4 films were evaluated through the degradation of the Orange II dye and of tetracycline hydrochloride under UV or visible light irradiation. The results show that compositional ratios and composition distribution of the ZnFe2O4 films prepared via SPPS played a key role on the photocatalytic activity. The SPPS route was demonstrated to be a promising method for the synthesis and the deposition of metal oxide (i.e. perovskite type and spinel type) films within a single-step for functional applications.

Copper in Natural Oxide Spinels: The New Mineral Thermaerogenite CuAl2O4, Cuprospinel and Cu-Enriched Varieties of Other Spinel-Group Members from Fumaroles of the Tolbachik Volcano, Kamchatka, Russia

This paper is the first description of natural copper-rich oxide spinels. They were found in deposits of oxidizing-type fumaroles related to the Tolbachik volcano, Kamchatka, Russia. This mineralization is represented by nine species with the following maximum contents of CuO (wt.%, given in parentheses): a new mineral thermaerogenite, ideally CuAl2O4 (26.9), cuprospinel, ideally CuFe3+2O4 (28.6), gahnite (21.4), magnesioferrite (14.7), spinel (10.9), magnesiochromite (9.0), franklinite (7.9), chromite (5.9), and zincochromite (4.8). Cuprospinel, formerly known only as a phase of anthropogenic origin, turned out to be the Cu-richest natural spinel-type oxide [sample with the composition (Cu0.831Zn0.100Mg0.043Ni0.022)Σ0.996(Fe3+1.725Al0.219Mn3+0.048Ti0.008)Σ2.000O4 from Tolbachik]. Aluminum and Fe3+-dominant spinels (thermaerogenite, gahnite, spinel, cuprospinel, franklinite, and magnesioferrite) were deposited directly from hot gas as volcanic sublimates. The most probable temperature interval of their crystallization is 600–800 °C. They are associated with each other and with tenorite, hematite, orthoclase, fluorophlogopite, langbeinite, calciolangbeinite, aphthitalite, anhydrite, fluoborite, sylvite, halite, pseudobrookite, urusovite, johillerite, ericlaxmanite, tilasite, etc. Cu-bearing spinels are among the latest minerals of this assemblage: they occur in cavities and overgrow even alkaline sulfates. Cu-enriched varieties of chrome-spinels (magnesiochromite, chromite, and zincochromite) were likely formed in the course of the metasomatic replacement of a magmatic chrome-spinel in micro-xenoliths of ultrabasic rock under the influence of volcanic gases. The new mineral thermaerogenite, ideally CuAl2O4, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption. It forms octahedral crystals up to 0.02 mm typically combined in open-work clusters up to 1 mm across. Thermaerogenite is semitransparent to transparent, with a strong vitreous lustre. Its colour is brown, yellow-brown, red-brown, brown-yellow or brown-red. The mineral is brittle, with the conchoidal fracture, cleavage is none observed. D(calc.) is 4.87 g/cm3. The chemical composition of the holotype (wt.%, electron microprobe) is: CuO 25.01, ZnO 17.45, Al2O3 39.43, Cr2O3 0.27, Fe2O3 17.96, total 100.12 wt.%. The empirical formula calculated on the basis of 4 O apfu is: (Cu0.619Zn0.422)Σ1.041(Al1.523Fe3+0.443Cr0.007)Σ1.973O4. The mineral is cubic, Fd-3m, a = 8.093(9) Å, V = 530.1(10) Å3. Thermaerogenite forms a continuous isomorphous series with gahnite. The strongest lines of the powder X-ray diffraction pattern of thermaerogenite [d, Å (I, %) (hkl)] are: 2.873 (65) (220), 2.451 (100) (311), 2.033 (10) (400), 1.660 (16) (422), 1.565 (28) (511) and 1.438 (30) (440).

Layered Nickel-Cobalt Oxide Coatings on Stainless Steel as an Electrocatalyst for Oxygen Evolution Reaction

In this work, we have obtained spinel-type nickel-cobalt oxide nanostructures on low-cost and easy-handling AISI304-type stainless steel substrate via simple potentiostatic electrodeposition. Nickel and cobalt hydroxide layers were formed by varying the deposition potential at the same time intervals (− 1.15 V for Ni(OH)2 and − 0.85 V for Co(OH)2). An electrolyte bath containing 0.05 M Ni(NO3)2, 0.05 M Co(NO3)2, and 0.1 M KNO3 was used for the electrodeposition. Structural analysis confirmed the formation of a spinel NiCo2O4 after thermal treatment. The influence of annealing temperature in the range of 473–1073 K on the films activity in OER has been investigated using 0.1 M NaOH. Nickel-cobalt oxide coatings demonstrated OER activity close to the benchmark IrO2 with the onset potential value of + 1.6 (vs. RHE), overpotential of 530 mV at 10 mA cm−2, and Tafel slope of 49 mV dec−1. Meanwhile, the electrocatalytic activity of separate Co3O4 and NiO is far smaller.

Transition metal based CuxNiyCoz-x-yO4 spinel composite solar selective absorber coatings for concentrated solar thermal applications

Solar selective absorber coatings, combining of nanostructured, ternary transition metal spinel structure and composite oxides were prepared by a series of transition metal (Co, Ni and Cu) based nitrate salts. A single-layered structure of crystalline phase spinel-type oxide AB2O4 in the framework of simple wet chemical route and dip coating method was prepared in the crystalline structure of CuxNiyCoz-x-yO4. The X-ray diffraction profile of the oxide film was found to coincide with that of crystalline [Cu2+0.31Co3+0.16Co2+0.53]A[Cu2+0.17Ni3+0.16Co3+1.67]BO4 in the ICDD database. Precursor salts were heated at a particular temperature to form hydroxy nitrate solution followed by suitable solvent with different binders to form adherent sol for dip coating technique. By optimizing sol concentration, withdrawal speed and annealing temperature, uniform absorber layer with solar absorptance of 0.91 and emittance of 0.14 were achieved in a single layer coating with a composite oxide formation. The optical, structural and morphological properties of the optimized coatings of single layer CuxNiyCoz-x-yO4 spinel and composite oxide have been characterized by UV–Vis–NIR spectrophotometer, emissometer, X-ray diffraction, field emission - scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy.

Superior sensitive NiFe2O4 electrode for mixed-potential NO2 sensor

A spinel-type metal oxide NiFe2O4 prepared by solid state synthesis was utilized as sensing electrode on a YSZ (yttria stabilization zirconia) based mixed potential NO2 sensor. NO2 sensing performances were evaluated at an operating temperature range of 350–500 °C. The sensor exhibited maximum response (81.3 mV to 100 ppm NO2) at 400 °C and optimal sensitivity of 82.8 mV/decade at 450 °C. Both cycling response and cross-sensitivity were evaluated, indicating good stability and selectivity. Furthermore, the EIS (electrochemical impedance spectrum) was also investigated to claim its sensing mechanism.

Structural, magnetic and dielectric properties of pure and Dy-doped Co3O4 nanostructures for the electrochemical evolution of oxygen in alkaline media

In this study, spinel-type cobalt oxide (Co3O4) and Co3-xDyxO4 (x = 0.04 and 0.05 molar ratio) nanoparticles were synthesized via combustion method at 700 °C. Crystallite nature, phase purity and thermal analysis of the prepared compounds were investigated by PXRD, FT-IR and TGA techniques. Structural analyses were performed by the FullProf program employing profile matching with constant scale factors. The results showed that the patterns had a main cubic structure with space group of Fd3m. The cell parameter data calculated by rietveld analysis showed that the cell parameters were nearly constant. The morphological and structural properties of the obtained materials were examined by FESEM and TEM images. Besides, the magnetic measurements of Co3O4 and Co3-xDyxO4 nanoparticles were performed by vibration sampling magnetometer (VSM). Coercivity (Hc) and remanent magnetization (Mr) were found to be reduced in Dy3+ doped Co3O4 while saturation magnetization (Ms) was increased moderately. The effect of dysprosium ion addition was also studied using cyclic voltammetry (CV) for the oxygen evolution reaction in an alkaline environment. The obtained data showed that the presence of Dy3+ exhibited a much higher oxygen evolution activity and lower over potential compared to Co3O4.

Sol–gel preparation of hierarchically porous magnesium aluminate (MgAl2O4) spinel monoliths for dye adsorption

Hierarchically porous spinel-type binary metal oxide MgAl2O4 with cocontinuous skeletons and interconnected macropores has been synthesized by a facile sol–gel method accompanied by phase separation, in which poly (ethylene oxide) (PEO) works as phase separation inducer to form micrometer-scale phase-separated macrochannels at the same time of sol–gel transition. The obtained xerogels exhibit in the form of a monolith with well-defined macropores and cocontinuous dense skeletons by adjusting the amount of PEO. The xerogel and those heat-treated at or below 600 °C are amorphous, and heat-treatment at or above 700 °C allows the precipitation of complete crystalline MgAl2O4 spinel with a macropore size of 0.7–0.9 μm, a porosity of 60–70%, and a BET surface area of 40–80 m2 g−1, without spoiling the macrostructure of monoliths. Three anionic dyes and two cationic dyes are selected as targeted adsorbates to investigate the selective adsorption ability of a hierarchically porous MgAl2O4 spinel. The resultant MgAl2O4 spinel shows a high affinity and adsorption rate toward anionic dyes Congo Red, Methyl Orange, and Methyl Blue. The maximum adsorption capacity of MgAl2O4 spinel toward these three anionic dyes are 2721.6 mg g−1 for Congo Red, 2469.7 mg g−1 for Methyl Orange, and 6771.9 mg g−1 for Methyl Blue, respectively.

Mixed-Oxide Catalysts with Spinel Structure for the Valorization of Biomass: The Chemical-Loop Reforming of Bioethanol

This short review reports on spinel-type mixed oxides as catalysts for the transformation of biomass-derived building blocks into chemicals and fuel additives. After an overview of the various methods reported in the literature for the synthesis of mixed oxides with spinel structure, the use of this class of materials for the chemical-loop reforming of bioalcohols is reviewed in detail. This reaction is aimed at the production of H2 with intrinsic separation of C-containing products, but also is a very versatile tool for investigating the solid-state chemistry of spinels.

(Keynote) Comparison of the Electrode Materials for Li and Na Ion Batteries

Secondary battery is becoming the key enabling technology for 3C products, electric vehicles (EVs) and energy storage system (ESS). Lithium-ion batteries (LIBs) with high energy density are widely used for mobile electronics, EVs and energy storage. Due to the abundant of resources, sodium-ion batteries (SIBs) have been considered as the promising candidate for large-scale energy storage system owing to the economic efficiency. LIBs and SIBs share similar concept and many materials. This presentation will summarize and compare their anode and cathode materials. Carbonaceous materials are commonly used for both of them as anode materials. However, well crystallized graphite is a good anode material for LIBs but not for SIBs. We have made hard carbon from sugar and anthracite for Li+ and Na+ storage. Sn, Sb, Si etc., which can alloy with Li and Na, show higher Na storage capacity. The rate capability of battery electrodes is highly dependent on the grain size, texture, and morphology of the electrode materials. An ordered, high surface area structure of electrochemically active materials on the nano scale can yield enhanced charge/discharge characteristics. Using nano materials as electrodes presents new opportunities for energy density, exceptionally high rate of charge and discharge, high cyclability, and low cost. The spinel Li4Ti5O12, well-known as a ‘zero-strain’ anode for lithium-ion batteries, can also store sodium, displaying an average storage voltage of 0.91 V and a reversible capacity of 155 mAh g1 and presents the best cyclability among all reported oxide-based anode materials. A three-phase separation mechanism, 2Li4Ti5O12 + 6Na+ + 6e- → 2Li7Ti5O12 + Na6LiTi5O12, has been confirmed. Furthermore, we also proposed many organic anode materials for SIBs including: Na2C8H4O4, Na2C6H2O4, Na2C14H6O4. In particular, we resolved the crystal structure of Na2C6H2O4 and found that it consists of alternating Na-O octahedral inorganic layer and π-stacked benzene organic layer in spatial separation. The experiment and calculation results reveal the Na-O inorganic layer provides both Na+ ion transport pathway and storage site, while the benzene organic layer provides electron transport pathway and redox centre. A large variety of cathode materials have been proposed based on the abundant knowledge developed on LIBs. They include layer- and spinel-structured transition metal oxides, and poly-anionic-type compounds. While layer-structured oxides with Co show high capacity for LIBs, the poly-anionic-compounds，spinel-type oxides and organic cathode materials are more promising for wide range of applications. Spinel-type oxides are used for LIBs only and certain nano-layered materials protected their surface and improve their cycling performance even at elevated-temperatures. High-voltage spinel LiNi0.5Mn1.5O4 cathode material has specific energy (~640 Wh/kg) due to the high operation voltage of ~4.7 V. The relatively inexpensive Ni and Mn in LiNi0.5Mn1.5O4 make this cathode material particularly desirable for large-scale applications. The surface regions (~ 2nm) show an irreversible migration of TM ions into lithium tetrahedral sites to form a Mn3O4-like structure. When the surface LiNi0.5Mn1.5O4 was modified by coating and superficial doping, the cycling performance of the material at elevated temperatures has been much improved and the Coulombic efficiency of discharge/charge is also obviously increased. Theoretical calculations analyses reveal that the stability of O at surface layer is enhanced by those surface modifications. Many layered oxide cathode materials with a general formula of NaxMO2 (M = Ni, Co, Mn, Fe, Cr, etc.) have attracted great attention for SIBs. We discovered that a novel Cu2+/Cu3+ redox couple is electroactive in Na containing layered oxides. On the basis of this important finding, we designed a new layered oxide, O3-Na0.9[Cu0.22Fe0.30Mn0.48]O2, showing unexpectedly superior stability against moisture and excellent electrochemical cycling stability. The material delivers a reversible capacity of 100 mAh/g with an average voltage of 3.2 V and stable cycling. A prototype sodium-ion pouch cell using our Cu based cathode and anthracite derived carbon anode is demonstrated to have an energy density of 117 Wh/kg and good cycling as well as high safety. The perspective of future practical application will be discussed based the comparison of materials.

Spinel-type cobalt-manganese oxide catalyst for degradation of Orange II using a novel heterogeneous photo-chemical catalysis system

A spinel-type Co-Mn oxide was designed and synthesized through a two-step oxidation-precipitation method at modest temperatures. The Co-Mn oxide was applied as the catalyst in the presence of NaHSO3 under visible light irradiation in order to establish the superiority of heterogeneous photo-chemical catalysis system. In the above system, the Co-Mn catalyst exhibited much better catalytic capability than that in either single photocatalysis or chemocatalysis system, implying that the Co-Mn catalyst could well combine photocatalysis and chemocatalysis to obtain the highest degradation efficiency of up to 94% within 40 min when using Orange II as the target pollutant. Recycling experiments results showed that the as-obtained catalyst has excellent stability and recyclability. Powder X-ray diffraction (XRD) analysis showed that the as-obtained Co-Mn catalyst had a cubic MnCo2O4.5 spinel structure. Because of relatively low temperature (180 ℃) synthesis, the catalyst was formed with nanoparticles (25–65 nm) and high specific surface area as confirmed by SEM and BET analyses. XPS indicated the presence of both manganese and cobalt species that serve as reactive sites for the catalytic oxidation reactions. Rational degradation mechanisms responsible for superior catalytic activity and durability were proposed based on a series of experimental results. The active species such as Mn(III), holes and sulfate and hydroxyl radicals were proposed to be responsible for the outstanding degradation results.

Improving Electrocatalysts for Oxygen Evolution Using NixFe3–xO4/Ni Hybrid Nanostructures Formed by Solvothermal Synthesis

Spinel-type oxides have been found to be active electrocatalysts for OER. However, their semiconductor character severely limits their catalytic performance. Herein, we report a facile solvothermal pathway for the synthesis of spinel-type NixFe3–xO4 oxides/Ni metal nanocomposites. The good electrical contact between the metal and semiconductor oxide interface and well-tuned compositions of NixFe3–xO4 spinel oxides are crucial to achieve better OER performance. Specifically, the NixFe3–xO4/Ni nanocomposite sample prepared from a metal precursor ratio of y = 0.15 [y = Fe/(Fe + Ni)] that results in an x value of about 0.36 exhibits catalytic activity with an overpotential of 225 mV to achieve an electrocatalytic current density of j = 10 mA cm–2 and a Tafel slope of 44 mV dec–1 in alkaline electrolyte. This study not only provides new perspectives to designing nanocomposite catalysts for OER but also opens a promising avenue for further enhancing electrocatalytic performance via interface and composition eng...

Site symmetry approach applied to the supercell model of MgAl2O4 spinel with oxygen interstitials: Ab initio calculations

In this study we simulate structural, electronic and phonon properties of MgAl2O4 spinel containing a single neutral oxygen interstitial (Oi) per crystalline L4 and L8 supercells, e.g., its dumbbell formed with one of the nearest regular oxygen atoms of the lattice (Oi-Oreg). Due to the splitting of the Wyckoff positions in supercell models of a perfect crystal, five possible Oi positions with different site symmetry have been identified and studied (C1, Cs, C3v D2d and Td). First principles hybrid HSE06 DFT functional calculations on perfect and defective spinel structures have been accompanied by geometry optimization. The calculated properties of spinel crystal (lattice constants, bulk modulus, band gap as well as frequencies of infrared- and Raman-active vibrational modes) are in a good qualitative agreement with the corresponding experimental data. The formation energy of Oi is found to be minimal for the interstitial site of the lowest symmetry (C1). The results obtained are important, in particular, for understanding the radiation and chemical stability as well as other key properties of MgAl2O4 spinel-type oxide crystals.

Simultaneous abatement of diesel soot and NOX emissions by effective catalysts at low temperature: An overview

ABSTRACTThe diesel engine generally achieves the highest fuel, energy, and thermal efficiency due to its very high compression/expansion ratio (14:1 to 25:1). Diesel engines can have a thermal efficiency that exceeds 50%. The main problem is that they emit more pollution like fine black soot particulates (C8H to C10H) and nitrogen oxides (NOX). These pollutants have been causing serious problems for human health and the global environment and also impacts on the engine. There are many types of catalysts investigated for simultaneous control of these two pollutants, i.e., platinum group metals (PGM; Pt, Pd, Rh, and Ir) based, spinel-type oxides, hydrotalcite, rare earth metal oxides, mixed transient metal oxides, etc. The high raw material cost of PGM catalysts has become a significant issue, so developing non-PGM catalysts are one of the promising challenges. There are no extra reductants required because soot catalytically oxidizes itself in the presence of NOX at a faster rate than molecular oxygen and simultaneously NOX is reduced to nitrogen. The order of oxidation potential of NOX to oxidized soot in comparison to molecular oxygen is as follows: NO2 > NO > O2. To meet the very strict EPA US 2010 and Euro VI regulations of particulate matter (PM) and NOX for heavy-duty and light-duty vehicular stringent emission, it is very important to apply the integrated catalytic systems to significantly remove PM and NOX simultaneously. Many papers related to simultaneous control of soot and NOX over different catalysts have been published but till now some of effective catalysts showing high conversion at low temperatures (possibly within the range typical of diesel exhaust: 150–450°C) have not been reviewed. Thus, this article provides a summary of published information regarding the effective catalysts, their preparation methods, properties, and application for simultaneous control of diesel soot and NOX.

Probing the Chemistry of Adhesion between a 316L Substrate and Spin-on-Glass Coating.

Hydrogen silsesquioxane ([HSiO3/2] n)-based "spin-on-glass" has been deposited on a 316L substrate and cured in Ar/H2 gas atmosphere at 600 °C to form a continuous surface coating with submicrometer thickness. The coating functionality depends primarily on the adhesion to the substrate, which is largely affected by the chemical interaction at the interface between the coating and the substrate. We have investigated this interface by transmission electron microscopy and electron energy loss spectroscopy. The analysis identified a 5-10 nm thick interaction zone containing signals from O, Si, Cr, and Fe. Analysis of the energy loss near edge structure of the present elements identified predominantly signal from [SiO4]4- units together with Fe2+, Cr2+, and traces of Cr3+. High-resolution transmission electron microscopy images of the interface region confirm a crystalline Fe2SiO4 interfacial region. In agreement with computational thermodynamics, it is proposed that the spin-on-glass forms a chemically bonded silicate-rich interaction zone with the substrate. It was further suggested that this zone is composed of a corundum-type oxide at the substrate surface, followed by an olivine-structure intermediate phase and a spinel-type oxide in the outer regions of the interfacial zone.

Secondary-Phase Formation in Spinel-Type LiMn2O4-Cathode Materials for Lithium-Ion Batteries: Quantifying Trace Amounts of Li2MnO3 by Electron Paramagnetic Resonance Spectroscopy

Spinel-type lithium manganese oxides are considered as promising cathode materials for lithium-ion batteries. Trace amounts of Li2MnO3 usually occur as a secondary phase in lithium-manganese spinels in the common high-temperature, solid-state synthesis, affecting the overall Li–Mn stoichiometry in the spinel phase and thereby the electrochemical performance. However, the formation of Li2MnO3 lower than 1 wt.% can hardly be quantified by the conventional analytical techniques. In this work, we synthesized lithium-manganese spinels with different Li/Mn molar ratios and demonstrate that electron paramagnetic resonance (EPR) enables quantifying trace amounts of Li2MnO3 below 10−2 wt.% in the synthesized products. The results reveal that the formation of Li2MnO3 secondary phase is favored by lithium excess in the synthesis. Based on the quantitative evaluation of the EPR data, precise determining Li–Mn stoichiometry in the spinel phase in Li1+xMn2−xO4 materials can be assessed. Accordingly, it is possible to estimate the amount of lithium on 16d-sites in the Li-rich manganese spinels.

Stability of a Cu0.7Co2.3O4 electrode during the oxygen evolution reaction for alkaline anion-exchange membrane water electrolysis

The electrode materials for oxygen evolution, especially non-platinum group metal oxides, have attracted increasing attention. Among the spinel-type transition metal oxides, Cu0.7Co2.3O4 powders were evaluated as a potential replacement for expensive dimensionally stabilized anode materials. Cu0.7Co2.3O4 powder for use as an electrode material for oxygen evolution in an alkaline anion-exchange membrane water electrolyzer was prepared using a thermal decomposition method. The Cu0.7Co2.3O4 powders heat-treated at 250 °C exhibited the same X-ray diffraction patterns without any secondary phases as the Co3O4 spinel structure did. The Cu0.7Co2.3O4 powders heat-treated at 250 °C for 30 minutes showed the smallest mean particle size of approximately 376 nm with the powders having a homogeneous shape and size distribution. The fine powders with a relatively homogeneous size distribution showed a higher current density during the oxygen evolution reaction. The lifetime of the Cu0.7Co2.3O4 electrode was relatively long at a low current density, but was quickly shortened due to physical detachment of the Cu0.7Co2.3O4 powders as the current density was increased. This study showed that the efficiency and the stability of Cu0.7Co2.3O4 powders during the oxygen evolution reaction were related directly to the active electrode area.