Amount Of Co3 Research Articles

Effects of B-site Co3+ doping on physicochemical characteristics and hydrogen production performance of novel LaCuxCo1-xO3 perovskite coated on monolithic catalyst in methanol steam reforming

A series of B-site Co3+-doped LaCuxCo1-xO3 (x = 1, 0.8, 0.6, 0.4, 0.2) perovskites were synthesized by solution combustion method and their physicochemical properties were comprehensively characterized. The perovskite-coated Cu foams were applied as monolithic catalysts for methanol steam reforming to produce H2. Results showed that an appropriate amount of Co3+ doping led to the stabilization of crystal structure, the reduction of particle size, the improvement of chemical constitution, the enhancement of reduction behavior, the decrease of acidity, the increase of specific surface area, and the optimization of surface chemical state. The monolithic catalyst loaded with LaCu0.4Co0.6O3 showed the highest methanol conversion rate and H2 production rate, the lowest CO selectivity, the best stability and the lowest carbon deposition. However, excess Co3+ resulted in a degradation of the catalytic performance. The findings of this work suggested that introducing Co3+ might be a promising way to enhance the activity of Cu species for obtaining a better Cu-containing perovskite-based monolithic catalyst.

Morphology engineering of Co3O4 spinel for efficient oxidation of lean methane at low temperature

Nowadays, the development of high-performance non-noble metal catalysts is an important research direction for controlling methane emissions from liquefied natural gas (LNG)-powered vehicles and vessels, and Co3O4 spinel has attracted great attention. In this work, Co3O4 catalysts with different morphologies (flower, sheet, particle, and cube) were synthesized by hydrothermal method and their catalytic performance was evaluated. The results showed that the flower-like Co3O4 (Co3O4-F) catalyst exhibited the highest activity in the lean methane oxidation with the T90 (temperature at the methane conversion of 90%) of 365 °C. Compared to other catalysts, Co3O4-F contained an amount of Co3+ sites and the weakest Co3+-O bond, which facilitated the extraction of active lattice oxygen and the initial oxidation of methane to intermediate products (formate and -COO-) on the catalyst surface. Meanwhile, the abundant oxygen vacancies on the surface of the Co3O4 catalyst could efficient activate O2 to form active oxygen species, which promoted the oxidation of intermediate products to CO2 and H2O. The methane oxidation over the Co3O4-F was confirmed to conform with Mars-van Krevelen mechanism. This work provides a facile way to enhance the methane oxidation activity of Co3O4 catalysts by modulating the morphology.

Suppressed phase separation in high-voltage LiNi0.5Mn1.5O4 cathode via Co-doping

Spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode material with high operating voltage and energy density. However, the poor rate performance caused by the two-phase reaction during charging and discharging limits its large-scale application. In this work, Co3+ doped LNMO cathode materials are prepared by co-precipitation method, and the effect of Co3+ doping replacing Mn4+, as well as the amount of Co3+ doping (LiNi0.5CoxMn1.5-xO4) are explored. Co3+ doping increases the content of Mn3+, thus improving the electronic conductivity of LNMO. Co3+ doping suppresses the phase transition of LNMO during discharging, which results in a smaller volume change and improves cycling stability. The presence of a solid solution intermediate allows for more uniform changes within the particles during the discharge process, thus increasing the diffusion rate of Li+ ion. LiNi0.5Co0.05Mn1.45O4 exhibits the best electrochemical performance compared to other samples, with a discharge specific capacity of 111.1 mAh g−1 after 500 cycles at 1 C and a capacity retention of 92.4%. At 10 C high rate, the specific discharge capacity is 106.8 mAh g−1. Our research reveals that Co3+ doping can improve the electrochemical performance of LNMO and provide a deeper insight into Co3+ doping of other cathode materials.

Influence of Co-Ni interactions on catalytic activity of xCo/NiO nanosheet catalysts in situ grown on monolithic cordierite for soot combustion

Co3O4-loaded NiO monolithic catalysts were successfully prepared on cordierite substrates using a simple hydrothermal and impregnation method. The mass transfer of gaseous reactants and products during soot combustion is facilitated by the constructed macroporous voids, thereby enhancing the soot-catalyst contact efficiency. The results demonstrate that the interaction of Ni and Co (Co2+ + Ni3+ ↔ Ni2+ + Co3+) leads to an increase in the amount of Co3+ cations, resulting in a higher quantity of oxygen vacancies. Besides the surface adsorbed oxygen (Oads), it demonstrates that the hydroxyl group (-OH) also acts as active oxygen species in soot oxidation. And, the impact of Co loading on the catalysts displays a volcano-type on the performance of soot oxidation. 0.5Co/NiO with the strongest CO-Ni interaction possesses the highest intrinsic activity. As a result, 0.5Co/NiO shows the highest activity with T50 at 382 °C in 600 ppm NO/10 % O2/N2 flow, as well as high stability and water resistance. Moreover, the prepared catalysts can efficiently catalyze NO to NO2, which possesses higher reactivity for soot oxidation than O2 and NO. Consequently, the as-designed Co/NiO monolithic catalysts hold great potential for applications in soot combustion and other non-homogeneous catalytic systems.

Effect of dopant on the thermal stability of core-shell ferrite nanoparticles

In this study, a series of core–shell ferrite nanoparticles were obtained by the thermal decomposition method of iron(III) acetylacetonate. Various amounts of Co3+, Mn3+, or Ni2+ ions as dopants were used. The prepared nanoparticles were treated at 500 °C for 24 h in the air atmosphere to determine the influence of doping on magnetite/maghemite crystalline structure and the following oxidation process. The nanoparticles before and after thermal treatment were evaluated by transmission electron microscopy, energy dispersive X-ray, X-ray diffraction and Mössbauer spectroscopy. The conducted studies show that doping primary structures by different 3d elements modulates the oxidation process of ferrite nanoparticles which, therefore, gives new possibilities for their application. However, the resistance to the oxidation of layered particles is different in comparison to the one-pot synthesis procedure. The susceptibility to oxidation varies not only due to the presence of different dopants in variable concentrations, but it also is dependent on layer positioning in the particle (core, shell, or both). The most protective element is Mn, and the least one – Co.

Beneficial effects of nickel promoter on the efficiency of alumina-supported Co3O4 catalysts for lean methane oxidation

In this work bimetallic Ni catalysts supported over Co-Al2O3 and monometallic Co-Al2O3 and Ni-Al2O3 catalysts were examined for the complete oxidation of methane. With a 30 % total metallic loading, the samples were synthesized by a sequential precipitation route. All samples were characterized by nitrogen physisorption, X-ray fluorescence, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, scanning-transmission electron microscopy, X-Ray photoelectron spectroscopy, and temperature-programmed reduction with hydrogen and methane. Their catalytic performance was investigated in the temperature range of 200–600 °C with a space velocity of 60.000 h−1. The bimetallic catalysts showed a better behavior in the oxidation reaction than the monometallic counterparts, mainly due to the good dispersion of Ni on the surface of the Co-Al2O3 samples. This has enabled the insertion of Ni2+ ions into the cobalt spinel lattice, which in turn provoked an increase in the amount of Co3+ species, and a subsequent enhanced mobility of oxygen species in the spinel. In this sense, the 5Ni/25Co catalyst showed the best performance, thus reducing the value of the T50 by 25 °C with respect to the monometallic catalysts.

Tuning the structure of Co3O4@MnOx catalyst by in situ redox approach for enhancing activity of the catalytic combustion of toluene

A novel in-situ redox method is proposed to prepare Co3O4 based catalysts with a core-shell-like structure toward the catalytic oxidation of toluene. The results of XRD, SEM and HRTEM reveal that Co3O4@MnOx with a core-shell-like structure was obtained after the precursor was partially oxidized by potassium permanganate. The as-prepared Co3O4@MnOx catalyst exhibits considerably high efficiency for the catalytic combustion of toluene, achieving 90% conversion of toluene at 233 ​°C that is at least 65 ​°C lower than that of the sole Co3O4 sample. The real reason is that Co3O4@MnOx is remarkably active than the other samples was explored by analyzing the results of a series of characterizations including Raman, XPS, TEM and H2-TPR. The results show that the catalytic activity of the samples is affected by the amount of Co3+ species, the concentration of oxygen species, and the content of oxygen vacancies to some extent, however, the result of H2-TPR indicates that their reactivity rather than the absolute content is the decisive factor for the activity of these catalysts. In addition, Co3O4@MnOx presents a satisfactory long-term stability, suggesting its great potential in industrial application.

Surface oxidation of cobalt carbonate and oxide nanowires by electrocatalytic oxygen evolution reaction in alkaline solution

The electrocatalytic water electrolysis is the most eco-friendly technique for hydrogen generation, which is governed by the electrode reaction kinetics involving cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) in common alkaline electrolytes. Cobalt oxide (Co3O4) and related compounds are the most efficient OER catalysts, replacing the noble metals. In this work, the surface oxidations of the cobalt carbonate (Co(CO3)0.5OH·0.11H2O) and Co3O4 nanowires during the OER are carefully investigated by contrasting the polarization curves, Tafel plots, and x-ray photoelectron spectroscopy (XPS) spectra, before and after the 1000th cyclic voltammetry (CV) cycling in 1 M KOH alkaline solution. The overpotentials required to reach a current density (j) of 20 mA cm−2 (η 20) are estimated to be 313 mV for the 300 °C-calcined Co3O4, 350 mV for the 400 °C-calcined Co3O4, 365 mV for the 500 °C-calcined Co3O4, and 373 mV for the cobalt carbonate (Co(CO3)0.5OH·0.11H2O). The Tafel slope of cobalt carbonate (Co(CO3)0.5OH·0.11H2O) nanowires is the highest at 93 mV dec−1, while it is measured to be 57 mV dec−1 for the 300 °C-calcined Co3O4, 47 mV dec−1 for the 400 °C-calcined Co3O4, and 79 mV dec−1 for the 500 °C-calcined Co3O4. As a result, the oxidation from Co2+ to Co3+ within Co3O4 during the OER is detected, which improves the OER activity. On the other hand, the formation of cobalt hydoxide is found on the surface of the Co3O4 nanowires during the OER in alkaline solution, which decreases the OER activity. For the surface oxidation of the cobalt carbonate (Co(CO3)0.5OH·0.11H2O) nanowires, the increase in the amounts of Co3+ and oxygen vacancy and the formation of O-C-O and carbonates are found, which highly enhance the OER activity. These findings indicate that the surface redox kinetics during the electrocatalytic reactions should be considered important in order to enhance the electrocatalytic activity, and furthermore can provide insight into future challenges in designing advanced electrocatalysts.

Nickel-doped Co4N nanowire bundles as efficient electrocatalysts for oxygen evolution reaction

Cost-efficient electrocatalysts composed of earth-abundant elements are highly desired for enhanced oxygen evolution reaction (OER). As a promising candidate, metallic Co4N already demonstrated electrocatalytic performance relying on specific nanostructures and electronic configurations. Herein, nickel was introduced as the dopant into one-dimensional (1D) hierarchical Co4N structures, achieving effective electronic regulation of Co4N toward high OER performance. The amount of Co3+ increased after Ni-doping, and the in-situ formed surface oxyhydroxide during OER enhanced the electrocatalytic kinetics. Meanwhile, the 1D hierarchical structure further promoted the performances of Co4N owing to the high electrical conductivity and abundant active-sites on the rough surface. As expected, the optimal Ni-doped Co4N with a Ni/Co molar ratio of 0.25 provides a small overpotential of 233 mV at a current density of 10 mAcm−2, with a low Tafel slope of 61 mV dec−1, and high long-term stability in 1.0 mol L−1 KOH. Following these results, the enhancement by doping the Co4N nanowire bundles with Fe and Cu was further evidenced for the OER.

Effect of Carbonate to Phosphate Molar Ratios on the Physico-Chemical Properties of Carbonated Hydroxyapatite Nanopowder

The aim of this study was to incorporate carbonate ions (CO3 2–) into the hydroxyapatite (HA) crystal structure followed by investigation on the effect of different carbonate to phosphate (CO3 2–/PO4 3–) ratios on the phase purity, crystal structure as well as CO3 2– content present in the apatite structure. CO3 2– substitution has been proposed to enhance the performance of HA-based material, particularly on the physico-chemical properties. Three different compositions of carbonated hydroxyapatite (CHA) powder with different CO3 2–/ PO4 3– ratios (namely, CHA 1:1, CHA 2:1 and CHA 4:1) were chemically synthesised by nanoemulsion method at 37°C and characterised for their physico-chemical properties. Results demonstrated that all as-synthesised powders formed single phase B-type CHA without any additional phases. Interestingly, an increasing amount of CO3 2– substituted into the apatite structure gives rise to the formation of CHA structure with a variation on their cell parameters and the degree of crystallinity. An increase in the CO3 2–/ PO4 3– ratio was also found to lead a higher amount of CO3 2– content present in the as-synthesised powder (in a range of 4 wt % to 10 wt %), which is comparable to the CO3 2– content found in the human bone mineral.

Anomalous behavior of displacement correlation function and strain in lanthanum cobalt oxide analyzed both from X-ray powder diffraction and EXAFS data

A combined X-ray powder diffraction (XPD) and high-resolution extended X-ray absorption fine structure (EXAFS) at the Co and Ga K-edges study has been performed for LaCoO3 and LaGaO3 ceramics, the latter sample was used as a reference without spin transitions. Based on the X-ray diffraction data, we have found that isotropic atomic displacement parameters (ADP) or mean-squared displacement of the Co–O bond exhibit gradual growth below ~50 K, wherein the strain dependencies testify rapid increase below 150 K for the LaCoO3 having rhombohedral structure. No similar features could be observed for LaGaO3 sample. Above ~100 K the isotropic ADP of the Co–O bond indicate a gradual growth, whereas strain curves show distinct bend near the spin-state transition temperature at about 150 K. According to the EXAFS data, the correlated parallel mean squared relative displacement (MSRD||) of Co–O and Ga–O bonds exhibit a gradual growth above 150 K; however, in the LaCoO3 this parameter is notably bigger. It is supposed that at low temperature the cobalt ions are dominantly in low-spin (LS) state, while certain amount of Co3+ ions located within the surface layer of the crystallines have high-spin state (HS). Temperature growth leads to a gradual transformation of the HS state of the cobalt ions into the highly-hybridized intermediate-spin (IS) state, while the cobalt ions located in the inner part of the crystallines remain LS configuration up to 150 K. Further temperature increase leads to a spin transition of the Co3+ ions located within the crystallines from the LS state into the IS one.

Effect of Co3+ substitution on the structure and magnetic properties of La0.6Ca0.4MnO3

The effect of cobalt doping on the structure and magnetic properties of polycrystalline La0.6Ca0.4Mn1−x Co x O3 (0 ≤ x≤0.3) has been studied. X-ray powder diffraction and magnetization measurements have been performed. A high-crystallized La0.6Ca0.4Mn1−x Co x O3 with an orthorhombic structure is obtained when the precursor is calcined at 900 °C in air for 3 h. Different amounts of Co3+ ion doping do not lead to the formation of another phase except diffraction peaks shifts slightly. With increase in Co3+ doping from x = 0, 0.1, 0.2, to 0.3, lattice parameters (b value) increase at first, then decrease. Magnetic characterization indicates that specific magnetization of La0.6Ca0.4Mn1−x Co x O3 decreases with the increase of Co3+ additional amount; substitution of Mn by Co3+ ion can markedly increase the coercive field of La0.6Ca0.4Mn1−x Co x O3, attributed that Co3+ doping can decrease Mn3+/Mn4+ ratio in La0.6Ca0.4Mn1−x Co x O3. La0.6Ca0.4Mn0.7Co0.3O3 at 100 K had the highest coercive field value, 1889.7 Oe. The coercive field of La0.6Ca0.4Mn1−x Co x O3 is between 35.1 and 114.7 Oe, even at 200 K, indicating that La0.6Ca0.4MnO3 and doped Co3+ La0.6Ca0.4Mn1−x Co x O3 continue being ferromagnetic at 200 K.

The disastrous effects of salt dust deposition on cotton leaf photosynthesis and the cell physiological properties in the Ebinur Basin in Northwest China.

Salt dust in rump lake areas in arid regions has long been considered an extreme stressor for both native plants and crops. In recent years, research on the harmful effects of salt dust on native plants has been published by many scholars, but the effect on crops has been little studied. In this work, in order to determine the impact of salt dust storms on cotton, we simulated salt dust exposure of cotton leaves in Ebinur Basin in Northwest China, and measured the particle sizes and salt ions in the dust, and the photosynthesis, the structure and the cell physiological properties of the cotton leaves. (1) Analysis found that the salt ions and particle sizes in the salt dust used in the experiments were consistent with the natural salt dust and modeled the salt dust deposition on cotton leaves in this region. (2) The main salt cations on the surface and inside the cotton leaves were Na+, Ca2+, Cl- and SO4 2-, while the amounts of CO3 - and HCO3 - were low. From the analysis, we can order the quantity of the salt cations and anions ions present on the surface and inside the cotton leaves as Na+>Ca2+>Mg2+>K+ and Cl->SO4 2->HCO3 ->CO3 -, respectively. Furthermore, the five salt dust treatment groups in terms of the total salt ions on both the surface and inside the cotton leaves were A(500g.m-2)>B(400g.m-2)>C(300g.m-2)>D(200g.m-2)>E(100g.m-2)>F(0g.m-2). (3)The salt dust that landed on the surface of the cotton leaves can significantly influence the photosynthetic traits of Pn, PE, Ci, Ti, Gs, Tr, WUE, Ls, φ, Amax, k and Rady of the cotton leaves. (4)Salt dust can significantly damage the physiological functions of the cotton leaves, resulting in a decrease in leaf chlorophyll and carotenoid content, and increasing cytoplasmic membrane permeability and malondialdehyde (MDA) content by increasing the soluble sugar and proline to adjust for the loss of the cell cytosol. This increases the activity of antioxidant enzymes to eliminate harmful materials, such as the intracellular reactive oxygen and MDA, thus reducing the damage caused by the salt dust and maintaining normal physiological functioning. Overall, this work found that the salt dust deposition was a problem for the crop and the salt dust could significantly influence the physiological and biochemical processes of the cotton leaves. This will eventually damage the leaves and reduce the cotton production, leading to agricultural economic loss. Therefore, attention should be paid to salt dust storms in the Ebinur Basin and efficient measures should be undertaken to protect the environment.

Nonprecious catalytic honeycombs structured with three dimensional hierarchical Co3O4 nano-arrays for high performance nitric oxide oxidation

A new type of noble metal-free catalytic honeycomb has been successfully developed by rational assembly of hierarchical Co3O4 nano-arrays on three dimensional ceramic honeycomb substrates. Different cobalt precursors were found to induce different assembly fashions for Co3O4 nano-array growth. Different Co3O4 growth mechanisms including “dumbbell aggregation” and “elongation–splitting” have been proposed to interpret the morphology evolution. The Co3O4 nano-array based catalytic honeycombs exhibit high performance catalytic NO oxidation with conversion efficiency as high as 80% at 275 °C. Such catalytic honeycombs were able to sustain their high NO conversion under either cyclic or long term steady isothermal operation and demonstrate excellent temperature fluctuation adaptability. The NO conversion capability of Co3O4 nano-arrays was determined by the amount of Co3+ on the surface, which acts as the active sites. Increased surface area enabled by small grain size and porous nature of nanowires promotes low temperature NO conversion. Thermal annealing at different temperatures was demonstrated to tune the porosity, grain size and thus the surface area of Co3O4 nano-arrays, which further influence the catalytic activity.

Study on the Performances of Nickel Hydroxide Coated with Ytterbium Hydroxide at High-Temperature

Abstract The surface of nickel hydroxide [Ni(OH)2] coated with ytterbium hydroxide [Yb(OH)3] and cobalt hydroxide [Co(OH)2] were studied and characterized by XRD, XPS, SEM and constant current recharge technology. The results show that the structure of β-Ni(OH)2 is hexagonal, Co exists mainly in the form of Co2+ with a small amount of Co3+, and the atomic ratio of Co and Ni on the sample surface is more than 8:1. The samples coated of 2 wt% Yb(OH)3 show the maximum discharge capacity and active material utilization rate at 65 °C (0.2, 1, 3 C). After 30 charge/discharge cycles, the discharge cycling stability and the discharge capacity of Ni(OH)2 coated with different contents of Yb (OH)3 are enhanced with increasing of content of Yb(OH)3 under different charge/discharge rates at 65 °C.

Stainless steel wire mesh-supported potassium-doped cobalt oxide catalysts for the catalytic decomposition of nitrous oxide

Structured catalysts consisting of potassium-doped cobalt oxide supported on stainless steel wire mesh were tested for the decomposition of N2O under dry and wet conditions. The cobalt oxide catalysts were prepared by the ammonia-evaporation-induced method. Of the several doping procedures tested, dropwise impregnation with potassium carbonate solutions provided the best catalytic results at lower K/Co molar ratios. Kinetic analysis of a potassium-doped catalyst yielded a reaction order on the N2O partial pressure slightly below unity (0.87). The activation energy values and the natural logarithms of the pre-exponentials factors for the different catalysts followed the classical compensation effect. This effect may be the result of a combination of competing reactions on different groups of active centers. Thus, cobalt ions affected by potassium display a low activation energy (∼40kJ/mol), whereas cobalt atoms unaffected by potassium display a higher activation energy equal to that of the undoped catalysts (∼106kJ/mol). The catalytic activity of the catalysts in N2O decomposition increases with the amount of reducible Co3+ ions, although there does not appear to be a direct relation between the amount of Co3+ ions and the textural and crystal properties of the catalysts. The addition of water produces some inhibition of the N2O decomposition reaction on K-doped catalysts, although catalytic activity is completely restored when the water is removed from the reaction stream. The catalysts prepared in this work were found to be among the most active, selective and stable catalysts reported in the literature.

Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3

The incommensurate modulated crystal structure of the hexagonal cobalt oxide Sr1.261CoO3 has been studied using a four-dimensional (4D) superspace profile analysis of neutron powder diffraction data. Sr1.261CoO3 is a composite crystal that consists of the [CoO3] and [2Sr] subsystems. The [CoO3] subsystem forms 1D chains that run parallel to the c-axis and consist of face-sharing CoO6 polyhedra with octahedral (Oh) and trigonal prismatic (TP) coordinations. The structure analysis reveals that the [CoO3] chains contain 73.9% Oh and 26.1% TP sites, and that the TP sites have longer Co–O bonds than the Oh sites:dav. =2.039(4) Å (TP) and 1.895(3) Å (Oh). The averaged Co bond valences are Co3.56(3)+ in the Oh sites and Co2.45(3)+ in the TP sites, suggesting that a considerable amount of Co3+ ions are mixed with Co4+ions in the Oh sites and with Co2+ ions in the TP sites. The observed magnetic susceptibility can be well explained assuming that the compound has the Co mixed-valence state with the spin configurations of S=0 low-spin state for Co3+(dε6), S=1/2 low-spin state for Co4+(dε5) and S=3/2 high-spin state for Co2+(dε5dγ2). The Weiss temperature, approximately 0.8 K, implies that Sr1.261CoO3 naturally assumes a Curie paramagnetic state, probably owing to the obstruction of the intrachain magnetic interaction by the nonmagnetic Co3+ ions. These results suggest that the nonmagnetic Co3+ ions play an essential role in the magnetism of Sr2γCoO3 systems.

<b>The surface behaviour and catalytic properties of Nd<sub>2-X</sub>Sr<sub>X</sub>CoO<sub>4±Λ</sub> mixed oxides</b>

The mixed oxides, Nd2-XSrXCoO4±λ (0.4 ≤ x ≤ 1.2), (λ = non-stochiometric oxygen) with the K2NiF4 structure were prepared by the polyglycol gel method and used as catalysts for NO reduction. The samples were investigated by IR, TPD, TPR, and XRD methods and iodometry and the effects of the coefficient x on the structure and catalytic activity of the samples were studied. The results show that the Nd2-XSrXCoO4±λ mixed oxides have the K2NiF4 structure; other phases are found when x < 0.4 and > 1.2. The amount of Co3+ and the lattice oxygen in Nd2-XSrXCoO4±λ increase with increasing x. The catalytic activity of Nd2-XSrXCoO4±λ for NO reduction is closely correlated with the concentration of oxygen vacancies and the amount of Co3+.KEY WORDS: A2BO4, Co-containing mixed oxide, NO reduction, Rare-earthBull. Chem. Soc. Ethiop. 2006, 20(2), 201-206.

Selective catalytic reduction of NO to N2 with copper and cobalt exchanged ZSM-5 zeolites: the effect of calcium addition

ZSM-5 catalysts containing either Cu or Co cations individually or Cu/Ca or Co/Ca cation combinations were prepared by ion exchange. These materials were tested as catalysts for the reduction of NO to N2 in the presence of propane or methane. Cu2+ and [Cu-O-Cu]2+ species were identified in ion exchangeable sites in the copper-containing catalysts. The amount of the latter cation increased with increasing copper content and in the presence of Ca2+ and was the most active in the reduction of NO. However, at temperatures higher than 400 ºC its activity decreased markedly. For cobalt-exchanged zeolites, Co2+ in charge-compensation sites or Co3+ in extra-framework precipitates were present in the catalysts. It was verified that the amount of Co3+ diminished with the presence of Ca2+. For the catalysts prepared in this study no significant differences in specific activity for the reduction of NO or for methane oxidation were observed in the presence of calcium.

Role of Doping and Dimensionality in the Superconductivity of NaxCoO2

We report a complete analysis of the formal Co3+/4+ oxidation state in NaxCoO2, in the interval 0.31 ≤ x ≤ 0.69. Iodometric titration and thermoelectric power confirm that a direct relationship between the Na content and the amount of Co3+ cannot be established in this system. Creation of a significant amount of oxygen vacancies accompanies Na-ion deintercalation, keeping the formal Co valence at 3.45+ for x ≤ 0.45. In light of new thermoelectric power data which reveals important differences between the hydrated (superconducting) and nonhydrated (nonsuperconducting) samples, we propose here that water plays an important “chemical” role beyond that of a spacer between the CoO2 layers.