Pure Co3O4 Research Articles

High catalytic performance of neodymium modified Co3O4 for toluene oxidation

Co-based catalysts are the most promising catalysts in catalytic oxidation of volatile organic compounds (VOCs). Precious metal doping is adopted to improve the catalytic activity of toluene on Co3O4 catalysts, but greatly increases its cost along with it. It is found that doping a small amount of rare earth (Ce, Pr, Sm and Nd) can dramatically promote the catalytic activity of Co3O4. Especially, the Nd-doped Co3O4 catalyst exhibits excellent catalytic activity with a toluene removal rate of 90% at 162.1 °C, which is even better than that of Pt-doped Co3O4. Compared with other rare earth metal doping, the Nd doping leads to a higher ratio of Co3+/Co2+ and has more oxygen vacancies. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments show that the lattice oxygen of Nd–Co sample can be utilized at a quite low temperature, while that of pure Co3O4 cannot engage in oxidation reaction when the temperature is below 200 °C, which visually demonstrates the main reason for the improved catalytic performance of Nd–Co catalyst.

Dual role of g-C3N4 microtubes in enhancing photocatalytic CO2 reduction of Co3O4 nanoparticles

The activity of photocatalytic CO2 reduction (PCR) remains inadequate due to the thermodynamically stable CO2 molecules and sluggish carrier kinetics. This work simultaneously adopts active site and heterojunction engineering to collaboratively enhance PCR. A heterojunction of g-C3N4 microtube-supported Co3O4 nanoparticle has been developed through the hydrothermal pretreatment and calcination processes. The g-C3N4 microtubes play dual roles in enhancing PCR of Co3O4: (1) they act as a substrate to support Co3O4 nanoparticles, thereby making small size and good dispersion of Co3O4 nanoparticles. The Co active sites can be highly exposed to accept photogenerated electrons and capture CO2 molecules; and (2) the p-type Co3O4 nanoparticles and n-type g-C3N4 microtubes build a p–n junction. An internal electric field is created to expedite the charge transfer. As a result, the g-C3N4 microtube-supported Co3O4 nanoparticle affords a significantly high turnover number (TON) of 24.72, which is 24-fold higher than that of the pure Co3O4 and comparable to state-of-the-art photocatalysts.

Co2.8Mg0.2O4 as a promising thermochemical energy storage material with lower reduction onset temperature and higher energy density

Co-based oxides have been considered as one of the most promising materials for thermochemical energy storage (TCES) systems, however, the high operation temperature limits their applications. Specially, when Co3O4-based materials are used in concentrated solar power (CSP) system, a large mirror field area is required to meet the high endothermic temperature, which significantly increases the cost of a CSP system. In addition, the high cost of Co-based materials also limits its application. Improving the energy density can effectively reduce the use of the materials. Thus, in this work, to reduce the reduction onset temperature and increase the energy density of Co-based oxides, the TCES performance of Co3-xMgxO4 oxides is investigated. Co2.8Mg0.2O4 shows the best TCES performance. The reduction onset temperature of Co2.8Mg0.2O4 is ∼775.6 °C, which is 133.7 °C lower than that of the pure Co3O4 (∼909.3 °C). Mg-decoration can also improve the energy density of Co3O4 by 8.02 %. Furthermore, the in situ XRD spectra of the oxides indicate that precipitation of MgO from the Co3O4 lattice during the reduction reaction result in a metastable structure of the oxide, which is conducive to its reduction reaction. Density functional theory calculations indicate that Co2.8Mg0.2O4 possessed a higher defect formation energy and shorter chemical bonds than the pure cobalt oxide, which result in its lower reduction onset temperature and higher energy density. The cost-benefit analysis results showed that Mg-decoration could significantly reduce the area of mirror field and the use of energy storage material for a CSP system.

Co3O4@Fe3O4/cellulose blend membranes for efficient degradation of perfluorooctanoic acid in the visible light-driven photo-Fenton system

Co3O4@Fe3O4/cellulose membrane was synthesized by coating rod-like MOF-derived Fe3O4 with Co3O4 nanoparticles and blending with cellulose solution, further applied in the visible light-driven photo-Fenton system for perfluorooctanoic acid (PFOA) degradation. In the H2O2/membrane/visible light system, the Electron paramagnetic resonance (EPR) analysis and scavenger experiment results suggested that PFOA degradation was a co-dependent mechanism via photogenerated electrons, photogenerated holes (h+) and various radical species, rather than a single active constituent. Co3O4@Fe3O4/cellulose membrane showed outstanding degradation performance, stability and recyclability under optimal conditions. Compared with pure Fe3O4 or Co3O4 nanoparticles, the Co3O4@Fe3O4/cellulose membrane can degrade around 94.5% PFOA within 180 min in reaction system, and the leached Fe and Co was only 0.05 and 0.49 ppm, respectively. Moreover, Co3O4@Fe3O4/cellulose was reused by rinsing with ultra-pure water and the degradation capacity was still 80.4% after five cycles. The degradation pathway of PFOA also was proposed based on UHPLC-MS analysis.

Novel n-MoSSe/p-Co3O4 Z-scheme heterojunction photocatalyst for highly boosting photoelectrochemical and photocatalytic activity

The development of stable, efficient photocatalyst for environmental antibiotics degradation is great significant and remains a major challenge. Herein, novel 2D/0D n-MoSSe/p-Co3O4 Z-scheme heterojunction catalysts (MSCO) are developed to combine the advantages of n-type MoSSe nanoplates and p-type Co3O4 nanoparticles. With an optimized Co3O4 loading ratio, the MSCO2 sample exhibited 7.8 and 28.8 times of photocurrent density more than that of pure MoSSe and Co3O4, and likewise showed 2.54 and 8.91 times of photocatalytic tetracycline hydrochloride removal rate more than that of pure MoSSe and Co3O4. Moreover, the heterojunction displayed outstanding recyclability after five cycles. The remarkably enhanced catalytic properties were mainly ascribed to the 2D/0D structure, built-in electric field between p-n heterojunction and electron transfer the Z-Scheme pathways which was helpful to promote the separation of photogenerated carriers. Additionally, the corresponding reaction pathway and photocatalytic mechanism were further elucidated by the results of the electron spin resonance (ESR) and high-pressure liquid chromatography-mass spectrometry (HPLC-MS). This research provided a new idea for the construction of Z-Scheme p-n heterojunction with 2D/0D structure in photocatalysis, photoelectrochemistry, and electrocatalysis.

Regulating electronic structure of hollow LaxCoyO4@NC by La incorporation for electrochemical oxygen evolution reaction

Developing efficient and low-cost electrocatalysts to substitute noble metals is crucial for oxygen evolution reaction (OER). Herein, we successfully synthesized hollow porous La-doped Co3O4 dodecahedral nanoparticles (LaxCoyO4@NC) through using ZIF-67 as precursor. Wherein, La could regulate electronic structure of Co3O4 and thus promotes the OER performance efficiently. La doped Co3O4 displays enhanced OER activity than pure Co3O4, as confirmed by experience results and density functional theory (DFT) calculation. Due to La doping, the ratio of Co2+ and Co3+ would increase obviously and generate new electronic states near the Fermi level. The La0.17Co2.83O4@NC exhibites excellent OER performance and high durability, which only requires an overpotential of 363 mV at the current density of 10 mA·cm−2 in alkaline medium and markedly outperforms Co3O4@NC (414 mV). These findings might provide a new strategy for controllable synthesis of transition metal nanocatalysts for high-performance OER electrocatalysis.

Heterostructured ultrafine metal oxides nanoparticles anchored on Co-MOF nanosheets obtained by partial pyrolysis for promoted oxygen evolution reaction

The anchor of functional materials on metal-organic frameworks (MOFs) nanosheets to precisely construct fascinated heterostructures for electrocatalysis is highly promising but challenging owing to the different interfacial thermodynamics and nucleation kinetics. In this work, we design and synthesize ultrafine metal oxides nanoparticles (NPs) homogenously distributed on cobalt-based MOF (Co-MOF) nanosheets for oxygen evolution reaction (OER) by a facile solvothermal reaction and subsequent partially controlled pyrolysis. The ultrafine Co3O4 NPs with a particle size of about 1.5 nm can be obtained from the dispersed elemental Co in Co-MOF and uniformly generated on the surface of the MOF, which is crucial for the formation of the unique heterostructure. The well-designed Co-MOF-350 exhibits an efficient electrocatalytic activity with a low overpotential of 239 mV at a current density of 10 mA cm−2 and a small Tafel slope of 63 mV dec−1, and an outstanding catalytic stability for OER, much superior to the pure Co-MOF and Co3O4 electrocatalyst. The intriguing OER performance mainly originates from the desirable combination of the abundant active sites, the extended electron transport channel between ultrafine metal oxides and Co-MOF nanosheets. More importantly, the work will help to design novel heteroarchitectured MOFs-based composites as efficient and robust electrocatalysts for practical applications.

In-situ oriented Sc-Co3O4 nanowire arrays for highly efficient ethanol detection

Improving the response of gas sensors has always been a hot research topic. Due to their unique electronic energy level structure, the compositing rare-earth (RE) element materials display unique properties in many fields such as catalysis, luminescence, and energy conversion. Along these lines, combining materials with the RE element of scandium (Sc) is considered a new method to optimize the performance of sensors based on the employment of ZIF-67 derived Co3O4 nanowire arrays. In this work, the Sc element was uniformly distributed on the surface of the Co3O4 nanowires, which were grown by enforcing hydrothermal and chemical bath-based methods. Based on the 30 % Sc composite Co3O4 nanowire array, the sensors show a maximum response of 32–100 ppm ethanol at a lower operating temperature (110 °C). The variation of the response was small range even after 35 days. Interestingly, the extracted response has increased more than three times that of the pure Co3O4 nanowire array devices. In addition, we tested the ethanol concentration range of 10–500 ppm and showed good performance. The gas-sensing properties of the sensors were systematically tested towards volatile organic compounds, including ethanol, acetone, methanol, etc. Based on the 30 % Sc composite Co3O4 nanowire array, the sensors still exhibit excellent selectivity to ethanol. The enhanced sensing performance is attributed to the strong catalytic effect of Sc and the modification of the surface morphology of Co3O4 by Sc. Our work provides an effective and promising method for improving the ethanol sensing performance of the ZIF-67 derived Co3O4 nanowires at low-temperature values.

Co2P/CoP quantum dots surface heterojunction derived from amorphous Co3O4 quantum dots for efficient photocatalytic H2 production

Amorphous/crystalline heterostructures show excellent potential in the hydrogen evolution reaction (HER) as they can significantly facilitate surface adsorption and redox reactions. Herein, a unique amorphous Co2P/crystalline CoP quantum dots (Co2P/CoP QDs) Type-II surface heterojunction was derived from amorphous Co3O4 QDs via phosphorization. The intimate contact between Co2P QDs and CoP QDs was conducive to charge transfer, thereby promoting surface reaction kinetics. The unique structure and properties were beneficial to providing more active sites and controlling the electronic structures thus making amorphous/crystalline composites show superior photocatalytic hydrogen (H2) production performance. Additionally, the amorphous Co2P QDs had a plethora of unsaturated bonds and abundant defects; the disordered structure led to increased active sites that promoted surface reaction kinetics. Due to the synergistic effect of the quantum confinement of QDs and the surface heterojunction, the charge transfer efficiency of Co2P/CoP QDs was extremely high, and high H2 evolution activity and photostability were achieved. The maximum H2 generation rate over the Co2P/CoP QDs composite reached 11.88 mmol h−1 g−1 with an apparent quantum efficiency (AQE) of 3.88 % at 420 nm, which is roughly 20-times that of the pure Co3O4 QDs. In addition, high photostability was realized; even the photocatalyst that stood for a week reached initial photoactivity. This work offers a novel idea for reasonably establishing amorphous/crystalline photocatalysts to achieve efficient H2 evolution.

Enhancing enzymatic activity of Mn@Co3O4 nanosheets as mimetic nanozyme for colorimetric assay of ascorbic acid

In nanozyme-based assays, increasing enzymatic activity is very desirable for enhancing sensitivity and lowering the detection limit. In this study, novel Mn doped cobalt oxide nanosheets (Mn@Co3O4 NSs) were synthesized by hydrothermal process. The obtained Mn@Co3O4 possessed enhanced dual-enzyme mimetic, oxidase and peroxidase, and can catalytically oxidize of 3, 3′, 5, 5′-tetramethylbenzidine (TMB), to a blue product of oxidized TMB. The enzyme kinetics were well-described mathematically using a common Michaelis-Menten and Lineweaver Burk model. The enzyme kinetics constant (Km) was found to be 0.15 mM, which is relatively low comparing with pure Co3O4 nanosheets (0.35 mM) and natural enzyme HRP (0.434 mM). Therefore, the efficient colorimetric method was achieved for determination of H2O2 and ascorbic acid. The limit of detection (LOD) of H2O2 was 8.0 μM and the linear range was 20–200 μM based on direct turn on of the peroxidase-like activity of Mn@Co3O4. While, for ascorbic acid detection based on turn-off approach, the linearity range for the ascorbic acid was 1–8 μM with LOD of 0.4 μM. Moreover, the colorimetric system exhibited good stability and selectivity toward the detection of ascorbic acid effectively in real samples (vitamin C tablets) with satisfactorily accuracy and precision.

Modulation of rGO-Co3O4 heterojunction with multi-walled carbon nanotubes for efficient ethanol detection

A carbon nanomaterials-modified MOF-derived Co3O4 p–p heterojunction was successfully constructed using a solution-combination-calcination method. The morphological and structural characteristics and their gas sensing performances were comprehensively investigated. Particularly, the synergistic effect between different carbon nanomaterials and Co3O4 mesoporous structures was carefully studied. The gas sensing results revealed that the sensor based on the CNT-rGO-Co3O4 nanocomposites exhibited better gas sensing properties toward the ethanol gas, including higher response, admirable antihumidity, and shorter response–recovery time than the other Co3O4 samples. The gas sensitivity of CNT-rGO-Co3O4 nanocomposites reached to be as high as 127.1, which was 5.8 times higher than that of a pure Co3O4 gas sensor when exposed to 100 ppm ethanol. The enhanced gas sensing performance of the sensor fabricated by the CNT-rGO-Co3O4 nanocomposites could be attributed to the promising synergistic effect between carbon nanomaterials and Co3O4 nanobox, implying that the heterojunction structure and coupling effect would dramatically optimize the gas sensing reaction process, resulting in improved gas sensing performance.

Microrecycled Co3O4 from waste lithium-ion battery: Synthesis, characterisation and implication in environmental application

Microrecycling based techniques are developed to synthesise phase pure porous Co3O4 using thermal isolation and controlled recycling pathways to achieve environmental outcomes that could manufacture and recycle hazardous spent Lithium-ion batteries (LIBs). The existing synthesising strategies for high surface area and small crystal grains of Co3O4 rely on raw materials, complex chemicals and experimental conditions. Herein the proposed facile technique produces Co3O4 with nanosized crystal grains and a large specific surface area of 79.2 m2 g−1 by utilising the cathode and anode material (CAM) of spent LIBs. The controllable synthesis of the Co3O4 also offers value added co-product of Lithium in the form of Li2CO3. Further utilisation of synthesised Co3O4 as a catalyst for toxic dye degradation offers an excellent opportunity to deliver benefits for society by creating a resource from waste that could treat other waste in our environment.

Fabrication of multi-layered Co3O4/ZnO nanocatalysts for spectroscopic visualization: Effect of spatial positions on CO2 hydrogenation performance

Controlled fabrication of spatial positions of different active sites on catalyst structures is critical to exploring the reaction mechanisms for CO2 hydrogenation. Herein, two isomorphous zeolitic imidazolate frameworks (ZIF-67 and ZIF-8) were used as sacrificial templates to synthesize multi-layered Co3O4/ZnO catalysts with tunable core-shell structures and well-controlled spatial positions. The multi-layered catalysts were then evaluated for the catalytic performance for CO2 hydrogenation. A series of characterization techniques were applied to investigate the morphology and structure of the Co3O4/ZnO composites with different spatial locations. Due to the unique multi-layered structure, the distinct interfacial structures, and the synergistic effects, the resultant core-shell structured Co3O4/ZnO nanocatalysts exhibited significantly enhanced activity as compared to their monometallic counterparts (pure Co3O4 and ZnO). In addition, the ZnO@Co3O4 with Co3O4 as shell showed significantly higher CO2 conversion (25%) than that of Co3O4@ZnO with ZnO as shell (0.82%). Furthermore, in-situ Diffuse Reflection Fourier Transform Infrared Spectroscopy (DRIFTS) analysis suggested that formate (HCOO*) and methoxy (CH3O*) species were the crucial intermediates in the CO2 hydrogenation over the Co3O4/ZnO composite nanocatalysts. However, pure ZnO could not activate the CO2; consequently, the use of the Co3O4/ZnO nanocatalysts derived from multiple-layered ZIFs structures provides new insights into improving the catalytic efficiency of CO2 hydrogenation.

High sensitivity and low detection limit of acetone sensor based on Ru-doped Co3O4 flower-like hollow microspheres

In this paper, we successfully prepared Ru-doped Co3O4 flower-like hollow microspheres by a simple hydrothermal method. The microstructure characterization results indicated the formation of well-organized microflowers with a size of 0.5–1 µm, which were composed of nanosheets. The gas sensing performances of sensors by using the synthesized Ru-doped Co3O4 hollow microflowers as sensing material were investigated. The 1 at% Ru-doped Co3O4 sensor showed the best acetone sensing performance and had a response 18.8–10 ppm acetone, which was almost 5.4 times that of pure Co3O4. Significantly, the sensor had an ultra-low detection limit, with a response value of 1.5–50 ppb acetone at 137.5 °C (30%RH). We propose a plausible mechanism for sensing performance improvement. Namely, the substitution of Ru4+ regulated the carrier concentration and induced the change of Co3O4 defect oxygen and chemisorbed oxygen.

Enhanced Removal of Methyl Violet Dye from Aqueous Solution by a Novel Co3O4@SiO2@TiO2-Ag Heterogeneous Semiconductor.

This research proposes the application of a novel photocatalyst including Co3O4@SiO2@TiO2-Ag nanocomposite with highly photocatalytic stability and core-shell structure for the removal of toxic methyl violet from aqueous solution. The removal of toxic dyes and organic contaminants from water is an outstanding research area among the scientists. Methyl violet is a toxic cationic pollutant that has a disruptive influence on humans. In this research, with an aim to remove methyl violet from the wastewater, we developed a new photocatalyst including Co3O4@SiO2@TiO2-Ag nanocomposite as an ecofriendly and low-cost nanostructure with high photocatalytic activity in order to reduce the risks of this pollutant from aqueous media. The Co3O4@SiO2@TiO2-Ag nanostructure was prepared via hydrothermal and sol-gel methods and the structure elucidation of the prepared photocatalyst was analyzed by different spectroscopy techniques, including XRD, FT-IR, FE-SEM, TEM, VSM and EDX. Photodegradation of methyl violet in the presence of different structures showed that Co3O4@SiO2@TiO2-Ag possesses superior photocatalytic activity (about 98% decomposed after 40 min) compared to the previous shells and pure Co3O4 NPs. Loadings of SiO2@TiO2-Ag nanocomposite over the Co3O4 surface led to the reduction in the bandgap energy of visible light and improvement in the photocatalytic activity of Methyl Violet dye f o r the aqueous phase decomposition. The remarkable benefits of this nanocomposite are high photocatalytic efficiency in the degradation of methyl violet (almost 100 % within 1 h), easy magnetic separation, low cost, and high chemical stability. The collected results demonstrated that the rate of degradation increased by increasing the irradiation time, while the rate of degradation decreased with increasing dye concentration.

Co3O4 anchored on ionic liquid modified PAN as anode materials for flexible lithium-ion batteries

Transition metal oxide Co3O4 is a candidate anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity and easy preparation. However, unmodified Co3O4 suffers from distinctly inferior rate capability and poor cycling stability. Here, we design and fabricate a three-dimensional (3D) island bridge structure (IBS) Co3O4 anchored into IL [BMIm][N(CN)2] modified PAN (Co3O4-PAN-IL) composite. The Co3O4 is uniformly dispersed microspheres, and IL modified PAN constitute a conductive network, which together form an IBS. The structure can effectively promote electron transfer, improve the specific surface area of the material, and alleviate the volume effect of cobalt oxide. More importantly, IL modified PAN has been considered as a highly conductive N-doping matrix after annealing. By virtue of these merits, the Co3O4-PAN-IL electrode demonstrates a high reversible capacity of 1499 mA h g−1 at 0.5C. After 800 cycles, the capacity of 1239 mA h g−1 was maintained, and the attenuation rate of each cycle was 0.022%. Compared with pure Co3O4, the electrochemical performance was significantly improved. The excellent electrochemical performance was due to the synergistic effect of nitrogen doping carbon network and uniformly dispersed Co3O4 particles. Furthermore, flexible pouch cells based on the cathode are further fabricated and demonstrate excellent electrochemical properties, highlighting the practical application of our deliberately designed electrode in flexible wearable electronics.

Synthesis of Nb2C MXene-based 2D layered structure electrode material for high-performance battery-type supercapacitors

The supercapacitor is a kind of electrochemical energy storage element, has attracted widespread attention, however, it is limited by a lack of ideal electrode materials with excellent cycle stability and high specific capacitance. To address this issue, we prepared Nb2CTx MXene-framework coated with Co3O4 to construct a robust 2D cross-linked structure. In this design, the self-assembly of Co3O4 between Nb2C MXene layers can effectively prevent the self-stacking of MXene sheets. The high conductivity and abundant active groups on the surface of MXenes provide a large number of active sites for the uniform distribution of Co3O4 on Nb2C MXene. The Co-MXene electrode achieves a specific capacitance of up to 1061 F g−1 at the current density of 2 A g−1, which is higher than the pure Co3O4 electrode and Nb2C MXene electrode. The asymmetric supercapacitors (ASCs) of Co-MXene//AC delivers specific energy densities (Es) of 60.3, 42.5, 31.0, 19.7 Wh kg−1 at specific power density (Ps) of 0.67, 2.0, 3.4, and 6.8 kW kg−1, respectively. The capacitance retention rate of 93% after 1000 cycles at 5 A g−1. The study provides a valuable guideline for fabricating satisfactory electrochemical energy storage devices by a feasible method.

New insight into degradation of chloramphenicol using a nanoporous Pd/Co3O4 cathode: characterization and pathways analysis

The growing chloramphenicol (CAP) in wastewater brought a serious threat to the activity of activated sludge and the spread of antibiotics resistance bacteria. In this study, a highly ordered nanoporous Co3O4 layer on Co foil through anodization was prepared as cathode for nitro-group reduction and electrodeposited with Pd particles for dechlorination to reduce CAP completely. After 3 h treatment, almost 100% of CAP was reduced. Co2+ ions in Co3O4 served as catalytic sites for electrons transfer to CAP through a redox circle Co2+–Co3+–Co2+, which triggered nitro-group reduction at first. With the presence of Pd particles, more atomic H* were generated for dechlorination, which increased 22% of reduction efficiency after 3 h treatment. Therefore, a better capacity was achieved by Pd/Co3O4 cathode (K = 0.0245 min−1, K is reaction constant) than by other cathodes such as Fe/Co3O4 (K = 0.0182 min−1), Cu/Co3O4 (K = 0.0164 min−1), and pure Co3O4 (K = 0.0106 min−1). From the proposed reaction pathway, the ultimate product was carbonyl-reduced AM (dechlorinated aromatic amine product of CAP) without antibacterial activity, which demonstrated this cathodic technology was a feasible way for wastewater pre-treatment.

Metal organic framework assisted Co-Ce mixed oxide catalyst for carbon monoxide and ethylene oxidation

A series of CeO2/Co3O4 mixed nanocomposites with various Ce loading were fabricated by the pyrolysis of MOFs (metal organic frameworks), and their catalytic performance were evaluated by CO and C2H4 oxidation reaction. The prepared catalysts inherited polyhedral morphology of ZIF-67 (Zeolitic Imidazolate Framework-67) nanoparticles. By means of the synergistic effect of two different transition metal oxides, the catalysts exhibited superior performance for CO and C2H4 oxidation. The results show that for 2% - 8% doping ratio of CeO2, the T50 (50% conversion temperature) of CO and C2H4 decreased by 32 and 33 °C, respectively, as compared with the MOF-assisted pure Co3O4 catalyst. Stability of the catalyst was greatly enhanced with optimal Ce doping to Co3O4. A number of characterization techniques were used to study the morphology and physicochemical properties of the prepared catalysts. With the incorporation of Ce, polyhedral Co-Ce catalysts promoted specific surface area and lower reduction temperature. Likewise, Co3+/Co2+ and Oads/Olatt improved with the addition of Ce, which played a significant role in CO and C2H4 oxidation at low temperatures.

Formation mechanism of strontium cobaltite containing equimolar amounts of Sr and Co from SrCO3 and Co3O4

Strontium cobaltite containing equimolar amounts of Sr and Co was produced by heating the mixture of SrCO3 and Co3O4 starting materials with a mole ratio of 1:0.333 under dynamic air atmosphere. The chemical reactions occurred during heating were determined and the intermediate and final products obtained at each critical temperature were characterized using TG/DTA-MS, ICP-OES, XRD and FT-IR analytical techniques. The volumetric analysis method (iodometric titration) and carbonation process were carried out to determine the oxygen stoichiometry of strontium cobaltite.It was determined by thermal analysis results that pure SrCO3 and Co3O4 were decomposed to SrO and CoO final products, respectively. Sr6Co5O15-β was formed by solid-state reaction between SrO and Co3O4 and by gaining O2 from air. Sr2Co2O5-δ was produced at elevated temperatures by solid-state reaction between Sr6Co5O15-β and Co3O4 by releasing O2. At temperature where the decomposition of SrCO3 is not completed and the decomposition temperature of Co3O4 is reached, firstly the formation of Sr6Co5O15-β and then Sr2Co2O5-δ takes place with CoO instead of Co3O4.Strontium cobaltite releases oxygen from its structure during heating as the temperature increases in the air atmosphere and it gains oxygen during cooling as the temperature decreases. Sr2Co2O5-δ is converted firstly to Sr6Co5O15 and CoO and then CoO reacts with O2 to form Co3O4 when cooled to the room temperature from the temperature it was obtained.