Effects of γ-radiation on the thermal stability of cobalt oxides

Pure cobaltic oxide, prepared by thermal decomposition of pure basic cobalt carbonate in air at 500°C, was subjected to different doses of γ-radiation varying between 5 and 50 M rad. The influence of γ-radiation on the thermal decomposition of cobaltic oxide to cobaltous oxide and the re-oxidation of CoO to Co₃O₄ was studied using DTA, with a controlled rate of heating and cooling. The effects of γ-radiation on the specific surface area (S_BET) and oxidation character of Co₃O₄ were also investigated.The DTA investigation revealed that γ-radiation effectively decreased the thermal stability of cobaltic oxide to an extent proportional to the dose employed. The maximum decrease in the thermal stability of 60% was attained by exposing Co₃O₄ solid to 30 M rad. γ-Irradiation, however, exerted no detectable effect on the re-oxidation of CoO by O₂ to Co₃O₄.The S_BET measurements showed that the small dose (5 M rad) of γ-radiation effected a decrease of 15% in the surface area of Co₃O₄, the higher doses (10–50 M rad) caused a further slight decrease of 18% in its surface area.γ-Irradiation was found to decrease the oxidation character of Co₃O₄ to an extent proportional to the dose employed.The decrease in the thermal stability of Co₃O₄ due to radiation is explained in terms of the decrease in the oxidation character of cobaltic oxide observed after subjecting the solid to γ-radiation.     

Effect of CeO<Subscript>2</Subscript> on the properties of the Pd/Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/cordierite catalyst in the conversion of CO,NO, and hydrocarbons

The effect of CeO₂ on the properties of the Pd/Co₃O₄-CeO₂/cordierite catalyst is a function of the method of its preparation. The catalyst obtained by the simultaneous deposition of cerium oxide and cobalt oxide showed high activity in the oxidation of CO (CO + O₂, CO + NO) and extensive oxidation of hexane (C₆H₁₄ + O₂). This behavior is due to the increased mobility of surface oxygen and increased dispersion of the catalyst components.     

Effect of epitaxial growth on the formation of the cobalt catalysts of the Fischer-Tropsch synthesis

Mixed oxides Co_xAl_yO₄ with different Al/Co ratios applied as supports for the catalysts of the Fischer-Tropsch synthesis were prepared using the solid-state chemical reaction. The Co_xAl_yO₄ supports were prepared by modifying gibbsite with various cobalt salts (acetate, nitrate, and basic carbonate). The use of basic cobalt carbonate gives the Co(20%)/Co_xAl_yO₄ catalyst, which provides an increased yield of hydrocarbons C₅₊ and a decreased methane content compared to the impregnation catalyst Co(30%)/Al₂O₃. The introduction of small amounts of rhenium additives makes it possible to enhance the yield of hydrocarbons C₅₊ (179 g m⁻³) and also to increase the selectivity with respect to the C₅–C₁₈ fraction. The introduction of basic cobalt carbonate into the support, most likely, creates favorable conditions for the epitaxial growth of the precursor of the active phase. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1856–1860, September, 2007.     

水热合成Co3O4的制备参数调变及其催化分解N2O性能

以十六烷基三甲基溴化胺（CTAB）为模板剂,通过调变CTAB浓度水热合成了氧化钴前驱体,焙烧制得棒状形貌的Co₃O₄,在其表面浸渍K₂CO₃溶液制得K改性的Co₃O₄催化剂,用于N₂O分解。用X射线衍射（XRD）、N₂物理吸附（BET）、扫描电镜（SEM）、X射线光电子能谱（XPS）、H₂程序升温还原（H₂-TPR）和O₂程序升温脱附（O₂-TPD）等技术对催化剂进行了表征,考察了CTAB/钴及尿素/钴物质的量比等制备参数对Co₃O₄催化分解N₂O活性的影响。结果表明,CTAB浓度为0.05 mol/L、CTAB/钴离子物质的量比为1、尿素/钴离子物质的量比为4时,所制备的Co₃O₄催化剂具有较高的N₂O分解活性,而K改性可以进一步提升其催化性能。K改性的Co₃O₄在有氧有水气氛中400℃下进行N₂O分解反应,50 h后N₂O转化率仍保持在91%以上。     

Binary α-Fe2O3–Co3O4 nanostructures for advanced oxidation process: Role of synergy for enhanced catalysis

Iron and its binary oxides are meticulously exploited for environmental remediations. However, only limited studies have been carried out on the degradation of industrial organics by advanced oxidation process. In this study, iron oxide, cobalt oxide, and iron–cobalt binary oxides were synthesized by a modified hydrothermal method as heterogeneous Fenton-like catalysts for the removal of methylene blue (MB) from wastewaters. The oxide nanostructures were characterized by different analytical techniques. Studying the effects of various parameters such as catalyst dose, MB concentration, and H₂O₂ concentration, the reaction conditions were optimized to enhance the removal of MB dye. The results revealed that α-Fe₂O₃–Co₃O₄ shows much higher activity than both Co₃O₄ and α-Fe₂O₃ for the degradation of MB at room temperature and beyond. The binary α-Fe₂O₃–Co₃O₄ shows degradation efficiency of 96.4% at 65 °C within 60 min. Furthermore, the binary α-Fe₂O₃–Co₃O₄ catalyst retains its activity for up to four successive cycles. A probable mechanism is also proposed, involving the generation of ‧OH radical as well as Fe²⁺/Fe³⁺ or Co²⁺/Co³⁺ redox couple of the binary α-Fe₂O₃–Co₃O₄ catalyst.     

Cobalt oxide supported gold nanoparticles as a stable and readily-prepared precursor for the in situ generation of cobalt carbonyl like species

A treatment of cobalt oxide supported gold nanoparticles (Au/Co₃O₄) under syngas atmosphere effectively generated a cobalt carbonyl-like active species in the reaction vessel. The preparation of Au/Co₃O₄ was quite simple and the in situ generated cobalt species could be used as a stable and easy handling alternative for dicobalt octacarbonyl without bothersome purification prior to use. The reactions, which are sensitive to the purity of the dicobalt octacarbonyl, such as the alkoxycarbonylation of epoxides and the Pauson-Khand reaction, smoothly progressed with Au/Co₃O₄.     

Convenient and Mild Epoxidation of Alkenes Using Heterogeneous Cobalt Oxide Catalysts

A general epoxidation of aromatic and aliphatic olefins has been developed under mild conditions using heterogeneous Co_xO_y–N/C (x=1,3; y=1,4) catalysts and tert‐butyl hydroperoxide as the terminal oxidant. Various stilbenes and aliphatic alkenes, including renewable olefins, and vitamin and cholesterol derivatives, were successfully transformed into the corresponding epoxides with high selectivity and often good yields. The cobalt oxide catalyst can be recycled up to five times without significant loss of activity or change in structure. Characterization of the catalyst by XRD, TEM, XPS, and EPR analysis revealed the formation of cobalt oxide nanoparticles with varying size (Co₃O₄ with some CoO) and very few large particles with a metallic Co core and an oxidic shell. During the pyrolysis process the nitrogen ligand forms graphene‐type layers, in which selected carbon atoms are substituted by nitrogen.     

Mechanism of the decomposition of cobaltous compounds in vacuo

The decomposition of cobaltous compounds (nitrate, hydroxide, carbonate, oxalate and oxyhydroxide) in vacuo has been investigated by magnetic methods and thermogravimetry. The mechanism is shown to be similar to that in air and begins with the formation of Co³⁺ ions in octahedral coordination. The formation of different final products (Co₃O₄, CoO and Co) has been attributed to the nature of the initial cobaltous compound. The results are in agreement with thermodynamic calculations.     

Effect of Li2O-doping on the thermal stability of cobaltic oxide

The influence of lithium oxide-doping on the thermal stability of Co₃O₄ was studied using DTA, TG, DTG and X-ray diffraction techniques. Pure and doped cobaltic oxide specimens were prepared by thermal decomposition of pure basic cobalt carbonate and the basic carbonate mixed with different proportions of LiOH, in air, at different temperatures between 500 and 1100°C.Pure Co₃O₄ was found to start partial decomposition when heated in air at 830°C yielding the CoO phase. The complete decomposition was effected by heating at 1000°C.Doping of Co₃O₄ with different proportions of Li₂O was found to much increase its thermal stability. The temperatures at which the doped oxide samples started to undergo decomposition were increased to 865, 910 and 1050°C for 0.375, 0.75 and 3% Li₂O-doped solids, respectively. The DTA revealed that the 1.5% Li₂O-doped cobaltic oxide did not undergo any thermal decomposition till 1080°C. The X-ray investigation showed that the prolonged heating of 1.5 and 3% Li₂O-doped solids at 1100°C for 36 h effected only a partial decomposition of Co₃O₄ into CoO. Heating of these solids at temperatures varying between 900 and 1100°C led also to the formation of a new lithium oxide cobaltic oxide phase, the composition of which has not yet been identified.The role of Li₂O in increasing the thermal stability of Co₃O₄ was attributed to the substitution of some of its cobalt ions by Li⁺ ions, according to Verwey and De Boer's mechanism, leading to the transformation of some of the Co²⁺ into Co³⁺ ions thus increasing the oxidation state of the cobaltic oxide lattice.     

Effect of the composition and structure of the precursor compound on the catalytic properties of cobalt-aluminum catalysts in the Fischer-Tropsch synthesis

The effect of preparation procedure on the anionic composition and structure of hydroxo compounds as precursors of Co-Al catalysts and on their catalytic properties in the Fischer-Tropsch synthesis was studied. The dynamics of changes in the composition and structure of the hydroxide precursors of Co-Al catalysts during thermal treatment and subsequent activation was studied by thermal analysis, IR spectroscopy, XRD analysis, and in situ XRD analysis with the use of synchrotron radiation. It was found that the precursor compounds prepared by deposition-precipitation of cobalt cations on γ- and δ-Al₂O₃ under urea hydrolysis conditions, which had a hydrotalcite-type structure and contained nitrate, carbonate, and hydroxyl groups, turtned into the oxide compounds Co_{3 ? x} Al _x O₄ (0 < x < 2) with the spinel structure in the course of thermal treatment in an inert atmosphere. The hydrogen activation of an oxide precursor led to the formation of cobalt metal particles through the intermediate formation of a cobalt(II)-aluminum oxide phase. The catalyst was characterized by high activity and selectivity for C₅₊ hydrocarbons in the Fischer-Tropsch synthesis.     

Co/AlPO4-5催化剂中Co的状态及其作用

本文用IR,TEM,FABMS,ESCA,XRD以及还原度的测定等方法,描述了Co/AlPO_4-5上Co_3O_4在氢作用下变成Co°,CoO以及未还原的Co_3O_4三种状态的还原过程和钴的颗粒分布的变化,并表明在还原过程中,可能有钴的簇状物生成,导致B酸形成。     

In situ FT-IR and TPD-MS study of carbon monoxide oxidation over a CeO2/Co3O4 catalyst

The forming of surface species during the adsorption of carbon monoxide (CO) and CO/O₂ on a CeO₂/Co₃O₄ catalyst was investigated by in situ Fourier transform infrared (FT-IR) spectroscopy and temperature programmed desorption-mass spectroscopy (TPD-MS). When CO was adsorbed on the CeO₂/Co₃O₄ catalyst, two types of surface species were distinguishable at room temperature: carbonate and bicarbonate. Surface carbonate was adsorbed on the cerium and cobalt, while the surface bicarbonate absorbed on the CeO₂/Co₃O₄ catalyst at 1611, 1391, 1216 and 830 cm⁻¹. Furthermore, the TPD-MS profiles revealed that the CeO₂/Co₃O₄ catalyst showed a greater amount of CO₂ than CO at 373 K. The CO desorption from the CeO₂/Co₃O₄ catalyst with increasing temperature showed that the order of thermal stability was surface bicarbonate < surface carbonate < interface carbonate species. Interestingly, the residual carbonate species could remain on the interface up to 473 K. The results revealed that surface bicarbonate could promote the conversion of CO into CO₂ for CO oxidation below 50 K.     

Synthesis of cobalt doped silica thin film for low temperature optical gas sensor

A modified sol–gel method was used to prepare cobalt doped silica thin film with a cobalt content of 10, 20 and 30 mol% (10Co, 20Co and 30Co). The prepared films were annealed at different temperatures in the range 400–1,000 °C, and their structural evolution examined. The mixed valence cobalt oxide, Co₃O₄, crystallizes only in the sample with the higher cobalt content, while cobalt silicate is the only crystalline phase detected in the sample 10Co and 20Co. Both the cobalt content and the temperature of heat treatment resulted to affect the nature of cobalt species dispersed in the silica matrix. The 30Co was selected for further investigations by FTIR spectroscopy to follow the structural evolution of 30Co film as function of the temperature and UV–Vis to get information on the cobalt valence state. The optical gas-sensing properties of 30Co films, containing Co₃O₄ as the major cobalt phase, were studied through the measuring of the film transmittance in dry air and in presence of dry air containing variable concentrations of polluting gases, CO and NO₂. The 30Co samples resulted to be highly sensitive to CO at room temperature. An explanation for the CO sensing characteristics, at low temperature, was proposed by referring to the physisorption-related mechanics of CO.     

富氧条件下Co/ZSM-5催化剂对C_3H_8选择还原NO_x的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C3H8选择性催化还原NOx性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co3+和Co2+物种,也有孔内的Co2+离子。富氧条件下Co/ZSM-5催化剂上C3H8选择性催化还原NOx的活性主要与ZSM-5载体孔外表面分散的CoOx物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoOx物种中钴离子可还原能力增强,C3H8选择性催化还原NOx的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NOx的转化率和催化剂比速率(k)的下降。孔外表面Co3O4晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C3H8的氧化燃烧,使C3H8选择性催化还原NOx的活性降低。     

富氧条件下Co/ZSM-5催化剂对C3H8选择还原NOx的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C₃H₈选择性催化还原NO_x性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co³⁺和Co²⁺物种,也有孔内的Co²⁺离子。富氧条件下Co/ZSM-5催化剂上C₃H₈选择性催化还原NO_x的活性主要与ZSM-5载体孔外表面分散的CoO_x物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoO_x物种中钴离子可还原能力增强,C₃H₈选择性催化还原NO_x的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NO_x的转化率和催化剂比速率（k）的下降。孔外表面Co₃O₄晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C₃H₈的氧化燃烧,使C₃H₈选择性催化还原NO_x的活性降低。     

氧化钴和氮掺杂碳纳米管纳米复合物的催化与容量性质(英文)

The nanocomposites based on cobalt oxide and nitrogen-doped carbon nanofibers (N-CNFs) with cobalt oxide contents of 10–90 wt% were examined as catalysts in the CO oxidation and supercapacity electrodes. Depending on Со3О4 content, such nanocomposites have different morphologies of cobalt oxide nanoparticles, distributions over the bulk, and ratios of Со3+/Co2+ cations. The 90%Со3О4-N-CNFs nanocomposite showed the best activity because of the increased concentration of defects in N-CNFs. The capacitance of electrodes containing 10%Со3О4-N-CNFs was 95 F/g, which is 1.7 times higher than electrodes made from N-CNFs.     

Synthesis of Nanorods of Crystalline Co3O4Using Carbon Nanotubes as Templates

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Nickel‐substituted cobalt ferrite nanoparticles supported on arginine‐modified graphene oxide nanosheets: Synthesis and catalytic activity

The amino acid arginine was used to modify the surface of graphene oxide nanosheets and then nickel‐substituted cobalt ferrite nanoparticles were supported on those arginine‐grafted graphene oxide nanosheets (Ni_0.5Co_0.5Fe₂O₄@Arg–GO). The prepared Ni_0.5Co_0.5Fe₂O₄@Arg–GO was characterized using flame atomic absorption spectroscopy, inductively coupled plasma optical emission spectrometry, energy‐dispersive spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, Raman spectroscopy, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The application of Ni_0.5Co_0.5Fe₂O₄@Arg–GO as a catalyst was examined in a one‐pot tandem oxidative cyclization of primary alcohols with o ‐phenylenediamine to benzimidazoles under aerobic oxidation conditions. The results showed that 2‐phenylbenzimidazole derivatives were successfully achieved using Ni_0.5Co_0.5Fe₂O₄@Arg–GO nanocomposite catalyst via the one‐pot tandem oxidative cyclization strategy.     

Polytypic transformations during the thermal decomposition of cobalt hydroxide and cobalt hydroxynitrate

The isothermal decomposition of cobalt hydroxide and cobalt hydroxynitrate at different intervals of temperature leads to the formation of Co₃O₄. The phase evolution during the decomposition process was monitored using powder X-ray diffraction. The transformation of cobalt hydroxide to cobalt oxide occurs via three phase mixture while cobalt hydroxynitrate to cobalt oxide occurs through a two phase mixture. The nature of the sample and its preparation method controls the decomposition mechanism. The comparison of topotactical relationship between the precursors to the decomposed product has been reported in relation to polytypism.     

不同形貌Co3O4和NiO的可控合成及光学性质

采用沉淀法,选择不同的钴盐和镍盐,以草酸为沉淀剂,磷酸三钠作为形貌导向剂,分别合成了具有特殊形貌的四氧化三钴和氧化镍。并对样品进行了微观结构、形貌和光学性质的表征。结果表明:在磷酸三钠的辅助下,四氧化三钴的晶体生长沿一维方向发展,氧化镍的晶体生长沿二维方向发展。紫外光谱测试表明,磷酸三钠参与下得到的四氧化三钴和氧化镍的禁带宽均增加。