Calcination Of Co Research Articles

Tuning electron orbits and reducibility of spinel Co3O4 via defect engineering for enhanced acetone sensing

Defect engineering is an effective method to regulate the electronic structure and chemical properties of functional materials to improve the catalytic, electrochemical and gas-sensitive properties. However, it is still a major challenge to rationally design defects to boost the amounts and activity of reaction sites. Herein, a strategy is proposed for regulating the content of Co2+ (Oh, octahedron) and oxygen vacancies in spinel Co3O4 (Co-LDH-x, x refers to temperature) via calcination of Co layered double hydroxides (Co-LDH). Where Co2+ (Oh) serves electrons in eg orbitals with a high energy state, and rich oxygen vacancies can act as strong Lewis acid sites to generate Lewis acid-base effects with lone pair electrons. Co-LDH-700 shows excellent repeatability, stability and selectivity in acetone sensing, as well as a low detection limit of 80 ppb. The response of the sensor to 100 ppm acetone is 262.3 at 185 °C, with a rapid response rate (9.8 s). In addition, the formation of the acceptor impurity CoCo′ establishes an acceptor level above the top of the valence band, which is beneficial to the formation of thermal-induced electrons. H2-TPR confirms that the increase of Co2+ content improves the reducing capacity and catalytic effect of Co-LDH-700 in the sensing process. This work proposes a method to increase active sites by modulating Co2+ (Oh) eg orbital and rich oxygen vacancies, which provides a new idea for enhancing the activity of sensitive materials.

Mechanism of peroxymonosulfate activation and the utilization efficiency using hollow (Co, Mn)3O4 nanoreactor as an efficient catalyst for degradation of organic pollutants

Development of efficient catalysts for peroxymonosulfate (PMS) activation and further understanding its mechanism on organic pollutants degradation is of significant importance for advanced oxidation processes (AOPs). Herein, hollow (Co, Mn)3O4 catalysts were synthesized by calcination of Co, Mn containing metal-organic frameworks (MOFs) and further used to evaluate the effectiveness of organic pollutants (Bisphenol A (BPA), atrazine (ATZ), and diethyl phthalate (DEP)) degradation by PMS activation. The PMS utilization efficiency in (Co, Mn)3O4/PMS system (36.4%) was estimated to be 28.0% and 43.8% higher than that of Co3O4/PMS and Mn5O8/PMS system, respectively. Notably, the metal leaching in (Co, Mn)3O4/PMS system was significantly suppressed. The utilization efficiency also reveals an inverse proportionality relationship with BPA mineralization but decreases with increasing initial pH value. A synergy between oxides of Co and Mn was perceived to enhance PMS utilization efficiency and BPA degradation. The results indicate enhanced catalytic performance with (Co, Mn)3O4 compared to Co3O4 derived from Co-MOF and other reported catalysts, with 99% of BPA degradation within 4 min. The oxidation mechanism was then proposed based on the electron paramagnetic resonance (EPR) and XPS results. Our findings might have contributed to designing heterogeneous catalysts for efficient PMS utilization in AOPs.

Synthesis of Co(OH)2@SiO2 core–shell based silver deposited cobalt oxide nanoflower for rechargeable Zinc-air batteries

The studies of core–shell nanoparticles have gained significant interests due to the high stability and probable template to form a core–shell complex by coating on them with organic or inorganic substances. The silica nanoparticle covered with cobalt is especially important because it has a chemically stable core. Co3O4-NF was synthesized by the calcination of Co(OH)2@SiO2 under atmospheric air for oxygen reduction and evolution reactions. After calcination, Ag deposition was performed to produce Ag@Co3O4-NF and their surface area reduces from 125.68 to 108.12 m2/g. The crystallanity and morphological features were observed by the X-ray diffraction (XRD) and scanning electron microscopy (SEM). Furthermore, Ag@Co3O4-NF catalysts exhibited superior electrochemical performance as a cathode material for Zinc-air batteries. The cyclic test for charging and discharging was performed for 500 h revealing Ag@Co3O4-NF a potential catalyst, having splendid stability for the OER and ORR.

Co3O4 Nanoparticles : Synthesis, Characterization and Its Application as Performing Anode in Li-Ion Batteries

In this research, a convenient, simple and rapid route for the preparation of Co3O4 nanoparticles using the calcination of Co(NO3)2∙6H2O at the presence of benzoic acid (1:1 weight ratio) is reported. Further, the as-prepared Co3O4 nanoparticles were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). XRD result confirmed the Co3O4 nanoparticles are pure phase and the average crystallite size for Co3O4 nanoparticles was found 77 nm. The TEM images reveal nanoparticles with size ranging from 50 to 100 nm, which is in conformity with the calculation of average crystallite sizes from XRD patterns. Furthermore, the prepared Co3O4 nanoparticles were investigated as an anode material for Li-ion batteries. Results showed that the Co3O4 nanoparticles exhibited excellent electrochemical performance and cycling stability, a capacity of 1127 mA h g-1 was obtained at 100 mAg-1 and the samples exhibited stable discharge behavior up to 130 cycles with high rate capability.

Co nanoparticles coupling induced high catalytic activity of nitrogen doped carbon towards hydrogen evolution reaction in acidic/alkaline solutions

The development of highly-efficient and noble-metal-free catalysts with low cost and high durability for hydrogen evolution reaction (HER) is of great importance to many energy-related technologies. This work reports that nitrogen-doped carbon coated Co nanoparticles encapsulated in bamboo-like nitrogen-doped carbon nanotubes (Co@NC/B-NCNTs), synthesized by a simple calcination of Co(NO3)2, melamine and P123, is a promising catalyst for HER in both acidic and alkaline solutions. In acidic solution, the Co@NC/B-NCNTs has the HER onset potential of ∼0 V and only needs an overpotential of 7 mV to drive the current density of 10 mA cm−2. Its HER catalytic activity is very close to that of Pt/C. In alkaline solution, its onset potential and overpotential to drive 10 mA cm−2 are 100 and 182 mV, respectively. Both the values are lower than those of many other catalysts reported. The DFT calculations show electronic coupling between Co nanoparticles and NC layer plays an important role in high catalytic activity of Co@NC/B-NCNTs. The Co nanoparticles can change the charge density distribution of the outer NC layer, affecting its properties for hydrogen adsorption and desorption. Additionally, the pyridinic N in the outer NC layer is calculated to be a promising active site for HER.

Morphology and defect modification on in-situ derived Co9S8-porous nitrogen-doped carbon as a bifunctional electrocatalyst for oxygen evolution and reduction

Exploration high-efficient bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of great significance for several renewable energy applications. In this paper, a catalyst composed of Co9S8 and porous carbon (Co9S8–C) is prepared first via the calcination of Co–S–C based precursor coating on carbon-fibre-paper (CFP) substrate under argon atmosphere. Then, the Co9S8–C is modified via the decomposition gas of dicyandiamide, thus Co9S8–N-doped carbon (Co9S8-NC) catalyst is synthesized. As revealed, the morphology and defect features are effectively modulated by the modification, suggesting the reduced particle sizes of Co9S8 component and obviously improved N proportion and various defects. As a result, Co9S8-NC represents excellent activities electrocatalytic performances toward OER and ORR, which surpass those of its three counterparts including Co9S8–C, Co9S8, and NC. A half-wave potential of 0.86 ​V versus RHE for ORR and a low overpotential of 280 ​mV ​at 10 ​mA ​cm-2 current density for OER are achieved, with the ΔE value of 0.64 ​V. Additionally, the catalyst also demonstrates desirable application prospect for Zn-air battery. The post-treatment method reported here might be utilized widespread to promote the synergistic effects between the Co-contained particles and N-doped carbons in composite catalysts.

Transition Metal Complexes of Mixed Bioligands: Synthesis, Characterization, DFT Modeling, and Applications

Divalent transition metal complexes [MGlu-Arg (H2O)]H2O and [MGlu-Arg (H2O)]H2O, where M = Co, Ni, Cu, and Zn, Glu = glutamic acid, and Arg = L-arginine, are prepared and characterized using different techniques. DFT and TD-DFT modelling validated and interpreted some experimental results. Weight loss technique reveals efficient corrosion inhibition action of these complexes towards aluminum metal at different temperatures. Our results point to corrosion inhibition through chemical adsorption on the aluminum surface. Additionally, a facile calcination of Co and Cu complexes at 550°C yields nanosized oxides of Co3O4, CoO, and CuO crystalline phases. The complexes show remarkable biological activities towards pathogenic bacteria and fungi. Moreover, in vitro anticancer activity evaluation of these complexes is achieved against hepatocellular carcinoma (HepG-2). The results are correlated with molecular descriptors such as chemical potential and hardness obtained from the frontier orbitals.

Pyrolyzing Co/Zn bimetallic organic framework to form p-n heterojunction of Co3O4/ZnO for detection of formaldehyde

he Co3O4/ZnO composites with porous and high specific surface were prepared by calcination of Co and Zn-based bimetallic organic framework (MOFs). The influence of the calcination temperature on structure and morphology of composite has been discussed by means of the analysis of XRD, FESEM, HRTEM and XPS spectra. Gas-sensing experiment reveals that the response of composite (Co/ Zn =4:1 At.) is 5 times higher than that of pristine Co3O4 to 10 ppm HCHO at 120 °C and exhibits a rapid response, good selectivity, and stability. Such excellent performance is attributed to the large specific surface area and porous structure resulting from pyrolyzing of MOFs framework, which is beneficial to gas adsorption, diffusion and surface reaction. This MOF-driven strategy is expected to be a promising method for preparation of other metal oxide composites and application in detecting toxic gas.

K-Doped Co–Mn–Al Mixed Oxide Catalyst for N2O Abatement from Nitric Acid Plant Waste Gases: Pilot Plant Studies

The K-doped Co–Mn–Al mixed oxide deN2O catalyst was prepared by calcination of Co–Mn–Al layered double hydroxide, subsequent impregnation with KNO3, and shaping into tablets of 5 mm × 5 mm. Tablets were tested for N2O decomposition in pilot scale reactor connected at the bypassed tail gas from the nitric production plant downstream of the SCR NOx/NH3 catalyst with the aim to perform kinetic measurements. Special attention was paid to study the changes in the catalytic performance, which was monitored using both the long-term catalytic test and the comparison of physical–chemical properties of the fresh and used catalyst. The changes in the surface composition, caused by the time-on-stream operation for 112 days in the pilot reactor, provided stable catalytic performance; average value of N2O conversion of 90 ± 6% at 450 °C was kept (GHSV = 11 000 m3 mbed–3 h–1). The obtained kinetic data were applied in modeling of a full-scale reactor for the N2O emissions abatement and can be used for estimation of the ...

Understanding Co‐Mo Catalyzed Ammonia Decomposition: Influence of Calcination Atmosphere and Identification of Active Phase

AbstractTo elucidate the effect of textural and chemical properties of catalysts and to discriminate the active phase are fundamental issues in heterogeneous catalysis, but they are often complicated by the nature of support adding a new dimension. In this work, metal amine metallate (Co(en)3MoO4) precursor was directly treated by calcination and prenitridation to understand these two issues in Co‐Mo catalyzed ammonia decomposition. The calcination atmosphere (i.e., Ar and Air) is found to remarkably affect the textural and chemical properties of catalysts, and air atmosphere is favorable for higher stable reactivity despite incomplete nitridation of the catalyst. Further prenitridation of the sample from the calcination of Co(en)3MoO4 under air gives rise to higher catalytic activity, and Co3Mo3N is suggested as the dominant active phase of Co‐Mo catalysts. The insights revealed here shed new light on the design of Co‐Mo catalysts for ammonia decomposition.

Synthesis of precursor-derived 1D to 2D Co3O4nanostructures and their pseudo capacitance behaviour

Co3O4 nanochains and nanosheets consisting of small single crystalline particles have been obtained by controlling the morphology of the precursor Co(CO3)0.5(OH)·0.11H2O via an environmentally friendly hydrothermal method without any addition of CO32− sources. The nanochains were constructed of single crystal grains connected one by one to form a necklace structure. The size of the grains in the nanochains were adjusted through controlling the calcination of Co(CO3)0.5(OH)·0.11H2O nanobelts at 350–600 °C. Porous Co3O4 nanobelts and irregular nanoparticles were created when the precursors were calcined at 300 and 700 °C, respectively. Through changing the volume ratios of ammonia to ethylene glycol in the solution, the morphology of the precursors was adjusted from one-dimensional (1D) nanobelts to a mixture of nanobelts and nanosheets and finally to 2D nanosheets. After calcination, the corresponding Co3O4 with a porous nanostructure was obtained. Importantly, when evaluated as electrode materials for supercapacitors, the as-prepared Co3O4 nanochains exhibit a superior supercapacitive performance with a capacitance of as high as 800 F g−1 which is higher than that from most previous reports, which is possibly due to their special short range order and long range disorder structures as demonstrated by high-resolution transmission electron microscopy. In contrast, the capacitance of porous nanobelts and nanosheets is low compared with that of nanochains. Because of their improved performance, the as-prepared Co3O4 nanochains will be utilizable as electrode materials for supercapacitors.

Optimization of Cs content in Co–Mn–Al mixed oxide as catalyst for N2O decomposition

A series of Co–Mn–Al mixed oxide catalysts with different Cs contents (0.5–4.6 wt%) was prepared by calcination of Co–Mn–Al hydrotalcite (Co:Mn:Al = 4:1:1), followed by impregnation by cesium salt (CsNO3, Cs2CO3) using the pore filling method. Chemical analysis, N2 sorption, temperature programmed reduction (TPR)-H2, temperature programmed desorption (TPD)-CO2 and TPD-NH3 and X-ray photoelectron spectroscopy (XPS) were used to characterize the catalysts. All prepared catalysts were tested for N2O catalytic decomposition in inert gas and in the presence of oxygen, water vapor and nitric oxide. The influence of Cs salts used for catalyst preparation and cesium content on catalyst activity were studied. A significant increase in catalytic activity with increasing amount of cesium promoter was observed without respect to the Cs precursor. The strong promotional effect of cesium is electronic in nature and is discussed in term of changes in surface composition and catalyst reducibility.

Ordered mesoporous Co3O4 for high-performance toluene sensing

Highly sensitive and selective toluene sensors based on ordered mesoporous Co3O4 have been successfully developed. The combined characterizations of X-ray diffraction (XRD) patterns, nitrogen adsorption–desorption isothermal, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicate that mesoporous Co3O4 with ordered mesoporous structure and high surface area has been successfully prepared by the nanocasting method using mesoporous silica (SBA-15) as hard template and Co(NO3)2·6H2O as cobalt source. It is also found that mesoporous Co3O4 thus obtained shows good response toward toluene with the concentrations ranging from 1ppm to 1000ppm. Furthermore, mesoporous Co3O4 also exhibits high selectivity for detection of toluene, compared to other interferences, such as ethanol, formaldehyde, ethanol, acetone, methanol and ammonia. Most importantly, mesoporous Co3O4 exhibits better sensing performance than that of non-porous Co3O4 obtained by direct calcination of Co(NO3)2·6H2O in the absence of any templates, which can be attributed to unique properties of mesopotous Co3O4, such as high surface area, open mesoporous structure as well as relatively small crystal size.

Uptake of Sc 3+ and La 3+ from aqueous solution using ethylenediaminetetraacetate-intercalated Cu–Al layered double hydroxide reconstructed from Cu–Al oxide

A Cu–Al layered double hydroxide intercalated with ethylenediaminetetraacetate (edta·Cu–Al LDH) was prepared by suspending Cu–Al oxide, obtained by the calcination of CO 3 2 − -intercalated Cu–Al LDH, in edta solution. It was found that the reconstruction of Cu–Al oxide to Cu–Al LDH was promoted with an increase in the temperature and time. The reaction in the pH range of around 8 suggests that Hedta 3− was intercalated in the interlayer of Cu–Al LDH. Edta·Cu–Al LDH was found to take up rare metal ions such as Sc 3+ and La 3+ in an aqueous solution at a pH of around 6–6.5. The uptake of Sc 3+ was caused not only by the chelating function of Hedta 3− in the interlayer but also by the chemical behavior of Cu–Al LDH itself. On the other hand, the uptake of La 3+ was caused only by the chelating function of Hedta 3− in the interlayer. The Hedta 3− in the interlayer of edta·Cu–Al LDH had the potential to form a chelate complex more preferentially with Sc 3+ than with La 3+.

Effect of high magnetic field annealing on the microstructure and magnetic properties of Co–Fe layered double hydroxide

The effects of high magnetic field (10 T) on the products obtained by calcination of Co–Fe LDH precursors at different temperatures were investigated. The XRD results indicated that Fe III substituted for Co III in Co 3O 4 to yield Co IICo IIIFe IIIO 4 under the calcination of Co–Fe LDH precursors at 400 °C. The products obtained by magnetic field annealing at 400 °C had a porous plate-like morphology, whereas the products without magnetic field annealing were composed of nanoparticles. It was seen that CoFe 2O 4 phase could be formed at low temperature (about 500 °C) under the magnetic field annealing. The grain size of products obtained by magnetic field annealing at 800 °C was larger than that of zero magnetic field. It was found that the saturation magnetization was significantly enhanced after magnetic field annealing, especially at lower temperature (≤600 °C). The possible reason for the effects on the microstructure and magnetic properties of products obtained by magnetic field annealing was discussed.

Catalytic combustion of methane over mixed oxides derived from Co–Mg/Al ternary hydrotalcites

Co x Mg 3 − x /Al composite oxides ( xCoMAO-800) were prepared by calcination of Co x Mg 3 − x /Al hydrotalcites ( x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, respectively) at 800 °C. The materials were characterized using XRD, TG-DSC, N 2 adsorption–desorption and TPR. The methane catalytic combustion over the xCoMAO-800 was assessed in a fixed bed micro-reactor. The results revealed that cobalt can be homogenously dispersed into the matrices of the hydrotalcites and determines the structure, specific surface areas and porosity of the derived xCoMAO-800 oxide catalysts. The thermal stability and homogeneity of the hydrotalcites markedly depends on the cobalt concentration in the hydrotalcites. The Co-based hydrotalcite-derived oxides exhibit good activity in the catalytic combustion of methane. The catalytic activity over the xCoMAO-800 oxides enhances with increasing x up to 1.5, but subsequently decreases dramatically as cobalt loadings are further increased. The 1.5CoMAO-800 catalyst shows the best methane combustion activity, igniting methane at 450 °C and completing methane combustion around 600 °C. The catalytic combustion activity over the xCoMAO-800 oxides are closely related to the strong Co–Mg/Al interaction within the mixed oxides according to the TG-DSC, TPR and activity characteristics.

Kinetic analysis of N2O decomposition over calcined hydrotalcites

Kinetics of N2O decomposition over catalyst prepared by calcination of Co–Mn hydrotalcite was examined in integral fixed-bed reactor (V˙/w=12–96 l gcat−1 h−1) at various N2O and O2 initial partial pressure at temperature range of 330–450°C. Kinetic data were evaluated by linear and non-linear regression method, 15 kinetic expressions were tested. Based on the obtained results a redox model of N2O decomposition was proposed. At low pressures of O2, adsorbed oxygen is formed by the N2O decomposition; the N2O chemisorption is considered as the rate-determining step. On the contrary, at high O2 pressure it could be assumed that adsorbed oxygen species appear as a result of O2 adsorption and the Eley–Rideal mechanism is the rate determining. N2O decomposition is well described by the 1st rate law at N2O and O2 concentrations typical for waste gases.

Preparation and characterization of CoO used as anodic material of lithium battery

The characteristics of CoO prepared from the calcination of Co(OH) 2 (precursor of CoO) in the N 2 atmosphere were analyzed, and the charge/discharge properties of CoO was also investigated in this paper. Increasing the calcination temperature from 200 to 900 °C the grain size of CoO increased from 6.59 to 31.5 nm, and the BET surface area decreased from 89.83 to 0.47 m 2 g −1. For CoO calcinated at 200 °C the maximum charge capacity, the coulomb efficiency and the irreversible capacity at the first cycle of Li/CoO battery were found to be 1233.57 mAh g −1, 98.46% and 305.87 mAh g −1, respectively. The irreversible capacity in the first cycle could be recovered in the following charge/discharge cycles.

Structure, Distribution, and Properties of Co Ions in Ferrierite Revealed by FTIR, UV–Vis, and EXAFS

Ion-exchanged Co ions and nitrosyl complexes in CoH– and CoNaK–ferrierites with a Co loading up to Co/Al=0.4 were investigated by diffuse reflectance UV–Vis–NIR, FTIR in the region of the skeletal and NO vibrations, and EXAFS measurements. Co(II) ion coordination, cation-induced perturbations of the framework T–O bonds of the hosted cationic sites, and Co–O distances of three typical ion-exchanged α-, β-, and γ-type Co ions in ferrierite are described. The α-type Co ions, coordinated to the rectangle of framework oxygens in the wall of the main ten-member ring channel, exhibit an open coordination sphere, weak bonding to the framework oxygens, and a high tendency to form dinitrosyl complexes upon NO adsorption. The β-type Co ions, the most populated ones in the whole concentration range, are coordinated to four framework oxygens of the deformed six-member ring of the ferrierite cavity at a distance of 1.99 Å. They exhibit medium-strength bonding to framework oxygens and, compared to the α-type Co ions, a substantially suppressed ability to bind dinitrosyls. The γ-type Co ions provide the highest perturbation of the hosted framework T–O bonds and thus the strongest bonding to framework oxygens attributed to the “boat-shaped” site of ferrierite. The tendency of the Co ions to relocalize under severe thermal/hydrothermal calcination of Co–ferrierite increased in the sequence γ<β⪡α, in agreement with the strength of bonding of the Co ions to framework oxygens at cationic sites.

Study of thermal dehydration of Co [formula omitted]Mg [formula omitted](H 2PO 4) 2·3H 2O

The dehydration and condensation reactions that take place during calcination of Co 1 2 Mg 1 2 (H 2PO 4) 2·3H 2O have been followed by means of thermal analyses under non-isothermal (dynamic) and quasi-isothermal-isobaric conditions. Isothermal calcination of starting binary dihydrogenphosphate was carried out in an electric oven at various temperatures and water vapour pressures. The reaction intermediates and products obtained were analysed by instrumental analytical methods and extraction experiments with solutions of water, acetone and 0.3 M HCl. Results have been obtained on the influence of water vapour pressure on the course, rate and yield of the condensation reactions and on the formation of the main product considered here, binary cyclo-tetraphosphate (tetrametaphospate) c-CoMgP 4O 12.