Mesoporous Co3O4 as an electrocatalyst for water oxidation

Mesoporous Co₃O₄ has been prepared using porous silica as a hard template via a nanocasting route and its electrocatalytic properties were investigated as an oxygen evolution catalyst for the electrolysis of water. The ordered mesostructured Co₃O₄ shows dramatically increased catalytic activity compared to that of bulk Co₃O₄. Enhanced catalytic activity was achieved with high porosity and surface area, and the water oxidation overpotential (η) of the ordered mesoporous Co₃O₄ decreases significantly as the surface area increases. The mesoporous Co₃O₄ also shows excellent structural stability in alkaline media. After 100 min under 0.8 V (versus Ag/AgCl) applied bias, the sample maintains the ordered mesoporous structure with little deactivation of the catalytic properties.      

Electronic and catalytic studies on Co1 − xCuxMn2O4 for CO oxidation

Spinels of the composition Co_{1 – x} Cu _x Mn₂O₄ (x = 0.0, 0.3, 0.5, 0.7 & 1.0) have been prepared by co-precipitation technique. These were characterized by X-ray diffraction, infra-red spectroscopy, atomic absorption spectroscopy and BET method. The solid state studies such as electrical resistivity, magnetic susceptibility and electron spin resonance have been carried out and attempts have been made to correlate with the catalytic activity of the compounds. The intermediate compositions displayed better catalytic activity than the end compositions for carbon monoxide oxidation due to the phenomena of synergism. Behaviour of the activity pattern has been explained based on cation distribution in tetrahedral (A) and octahedral (B) sites. Crystallographic phase transition is observed from tetragonal to cubic at x > 0.5 by substitution of Cobalt with Copper.     

Preparation and characterization of nanosized gold catalysts supported on Co3O4 and their activities for CO oxidation

Gold catalysts supported on Co3O4 were prepared by co-precipitation (CP), deposition-precipitation (DP), and impregnation (IMP) methods. The Au/Co3O4 catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) to understand the different activities for CO oxidation with different preparation methods. Gold particles below 5 nm supported on Co3O4 by DP method were found to be more exposed to the surface than those by CP and IMP methods, and this catalyst was highly active and stable in CO oxidation. Finally, catalytic activity of Au/Co3O4 catalyst for CO oxidation was strongly dependent on the gold particle size.     

Characterization and catalytic performance of Co/SBA-15 supported gold catalysts for CO oxidation

Cobalt-containing SBA-15 supported gold catalysts for low-temperature CO oxidation were prepared and characterized by N₂ adsorption/desorption, X-ray diffraction, transmission electron microscopy, inductively coupled plasma-atom emission spectroscopy and X-ray photoelectron spectroscopy techniques. The effects of cobalt and gold content on the catalyst activity were investigated in detail. Among them, 2% Au/40% Co/SBA-15 shows the highest activity, its complete conversion temperature for CO is at 273 K. It was believed that both the dispersion of Co₃O₄ and the high surface areas caused by SBA-15 contribute to the good activities of cobalt-containing SBA-15 supported gold catalysts. Furthermore, the strong metal-support interaction between gold and cobalt oxides is greatly related to the catalytic performance.     

Effect of calcination temperature on structural,optical and antibacterial properties of ball mill synthesized Co3O4 nanomaterials

Journal of Materials Science: Materials in Electronics - In the present work, we have investigated the role of calcination temperature in altering the structural, optical and antibacterial...     

Synthesis,characterization and catalytic activity of Au supported on functionalized SBA-15 for low temperature CO oxidation

SBA-15 functionalization with 3-mercaptopropyltrimethoxysilane was used to prepare a supported gold catalyst for the low temperature CO oxidation reaction. Catalytic runs were performed at atmospheric pressure and T = 40–150 °C and the influence of different thermal treatments of the sample prior to reaction was studied. The modifications induced by the pre-treatments in the physico-chemical properties of both the carrier and the disperse phase were investigated by chemical analysis, CHS elemental analysis, N₂ adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), solid state cross-polarization magic-angle-spinning nuclear magnetic resonance spectroscopy (CPMAS NMR) of ²⁹Si and ¹³C and Fourier transform infrared spectroscopy (FTIR). The pre-treatment conditions were found to strongly affect both the gold particle size and the nature of the Au surface species. An appreciable catalytic activity was found on samples treated at 600 °C in H₂/He atmosphere, provided that the functionalizing agent had been completely removed by a previous high-temperature calcination.     

NiO nanorings and their unexpected catalytic property for CO oxidation

Nickel oxide (NiO) nanorings were synthesized by controllable thermal decomposition of precursor Ni(OH)(2) nanoplates obtained via the reaction between Ni(NO(3))·6H(2)O and NaOH under hydrothermal conditions. The process of their formation was investigated and an unexpected catalytic property of this novel-shaped material is reported for CO oxidation.     

Ultrasmall Co3O4 Nanocrystals Strongly Enhance Solar Water Splitting on Mesoporous Hematite

The synthesis of crystalline, nonagglomerated, and perfectly dispersible Co₃O₄ nanoparticles with an average size of 3–7 nm using a solvothermal reaction in tert‐butanol is reported. The very small size and high dispersibility of the Co₃O₄ nanoparticles allow for their homogeneous deposition on mesoporous hematite layers serving as the photoactive absorber in the light‐driven water splitting reaction. This surface treatment leads to a striking photocurrent increase. While the enhancement of hematite photoanode performance by cobalt oxides is known, the preformation and subsequent application of well‐defined cobalt oxide nanoparticles are novel and allow for the treatment of arbitrarily complex hematite morphologies. Photoelectrochemical and transient absorption spectroscopy studies show that this enhanced performance is due to the suppression of surface electron–hole recombination on time scales of milliseconds to seconds.     

Synthesis of mesoporous Co/Ce-SBA-15 materials and their catalytic performance in the catalytic oxidation of benzene

Cerium-containing SBA-15 mesoporous materials, with different Ce/Si molar ratios, were synthesized by a direct hydrothermal synthesis method and further modified by impregnation with 10, 15 and 20 wt.% Co. Characterizations by powder X-ray diffraction (XRD), N₂ sorption, inductively coupled plasma (ICP) and UV-vis spectroscopy were carried out. The small-angle XRD and N₂ sorption characterizations showed that these Co supported materials have less-ordered mesoporous structures with partial blockage of pores, and their specific surface area, pore volume and pore size were relatively lower than those of unsupported cerium-containing SBA-15. Spinel Co₃O₄ constituted the predominant cobalt phase in the prepared catalysts, and CeO₂ was also detected. All the Co supported catalysts exhibited high catalytic activity in the oxidation of benzene.     

Capacity fading of LiMn2O4 electrode: Influence of calcination temperature

Spinel-type Li-Mn oxides of formula LiMn_2–x O₄ were prepared by the Pechini method in the range of 600–850°C for 4 h. These spinels were investigated by X-ray powder diffraction, SEM (scanning electron microscope), ICP, chemical titration and galvanostatic cycling at 0.2C rates. The effect of calcination temperature is evaluated. With increasing calcination temperature, Mn valence-state of the powder decreased while size of powder increased. The cycle life of the powder decreases with increasing calcination temperature. The results indicated that the Mn valence-state and powder size of cathode powder should be important variables to improve cycle life. The effect of cell polarization effect on the cycle life is also discussed.     

Hierarchical laminated Al2O3 in-situ integrated with high-dispersed Co3O4 for improved toluene catalytic combustion

Hierarchical structure and surface properties of selective support afford some special effects on the catalytic activity, which could be tuned to achieve improved performance. Herein, using a combination of hydrothermal coprecipitation and thermal processing, we integrated highly-distributed Co₃O₄ spinel nanospecies on laminated hierarchically structured Al₂O₃ which could be used as a highly efficient VOCs treatment catalyst. Impressively, compared to Co-free Al₂O₃ counterpart (S_BET = 188.2 m²·g^?1), these obtained Co₃O₄ spinel functionalized catalysts are endowed with adjustable Co loading, optimized Co activity state, and obviously improved hierarchically structural properties (S_BET = 274.7 m²·g^?1). The microporous and mesoporous structures both existed in the obtained Al₂O₃, which is beneficial to the heterogeneous catalytic reaction process. The results reveal that the proper Co loading in the hierarchically structured Al₂O₃ could enable the rational modulation of catalytic activity in the combustion of toluene and exceeds the commercial 5 wt% Pd/C catalyst in the light of total catalytic oxidation ability. This developed heterogeneous Co₃O₄ compositing hierarchically structured Al₂O₃ provides a significant potential value for practical VOCs treatment.     

SnO2/Fe2O3 nanocomposites: Ethanol-sensing performance and catalytic activity for oxidation of ethanol

SnO₂/Fe₂O₃ nanocomposites have been prepared over the entire composition range (0–100 mol% Fe₂O₃) through precipitation from solution, and their ethanol-sensing performance (10–200 ppm C₂H₅OH) was evaluated using electrical conductivity measurements in the temperature range 150–450°C. The sensing performance of the nanocomposites is shown to strongly depend on their composition. The Fe₂O₃-rich (>70 mol% Fe₂O₃) nanocomposites offer a large C₂H₅OH response and low sensitivity to ambient humidity. The oxidizing and acid properties of the nanocomposites have been studied using temperature-programmed hydrogen reduction and ammonia desorption measurements, and their catalytic activity for oxidation of ethanol was assessed by gas chromatography mass spectrometry in a flow system. The results indicate that increasing the Fe₂O₃ content of the nanocomposites reduces the density of acid centers on their surface and enhances their activity for oxidation of ethanol.     

Effect of temperature on the catalytic oxidation of CO over nano-sized iron oxide

Nanocrystallite iron oxide powders were prepared by co-precipitation method using highly purified FeCl₃ and NH₄OH solution. The prepared powders were tested for the catalytic oxidation of CO to CO₂. The effect of oxidation temperature on the catalytic reaction was isothermally investigated using advanced quadrpole mass gas analyzer system. The mechanism of the catalytic oxidation reaction was estimated from the experimental data. Fe₂O₃ nanocrystallite of 78 nm shows a good response towards catalytic CO oxidation at the temperature range 200–500 °C. The catalytic oxidation efficiency reached 98% at 400–500 °C. The reaction was found to be first order with respect to CO. The average activation energy of the reaction was found to be 26.3 kJ/mol which is smaller than the values reported in the literatures. The mechanism of CO catalytic oxidation was investigated by comparing the CO catalytic oxidation data in the absence and presence of oxygen. It was found that the catalytic oxidation of CO over Fe₂O₃ nanocrystallite proceeded by adsorption mechanism. Based on the experimental results, Fe₂O₃ nanocrystallite powders can be recommended as a promising catalyst for CO oxidation.     

Mesoporous Co3O4 nanowire arrays for lithium ion batteries with high capacity and rate capability

We report the high capacity and rate capability of mesoporous Co3O4 nanowire (NW) arrays as anodes in Li ion batteries. At a current of 1C, the NW arrays maintain a capacity of 700 mAh/g after 20 discharge/charge cycles. When the current is increased to 50C, 50% of the capacity can be retained. With their ease of large area synthesis and superior electrochemical properties, these Co3O4 NW arrays will be interesting for practical Li ion batteries.     

CuFe2O4催化剂的制备及其NH3-SCR催化性能研究

通过微波法合成了金属有机骨架材料Cu-MIL-101(Fe),然后以此为前驱体煅烧制备了CuFe2 O4催化剂,并考察了反应温度、催化剂用量、空速、SO2、H2 O等因素对催化剂NH3-SCR催化性能的影响.测试结果表明CuFe2 O4催化剂可以在250～450℃的宽温度区间保持90％以上的脱硝效率,反应前后催化剂无明...     

催化相转化法制备纳米铁酸镍及性质研究

用催化相转化法在不同初始浓度，不同pH值下．在液相中短时间内合成出了纳米铁酸镍微晶．利用XRD、TEM对产物进行了表征，并测定了产物的磁化强度、密度及比表面。结果表明，该方法制备的纳米级铁酸镍具有超顺磁性，粒径小于20nm。     

Co3O4电化学电容电极材料的制备及性能研究

利用水热法,以硝酸钴为原料,分别以碳酸氢铵、六次甲基四胺为沉淀剂,制备了Co3O4。借助X射线衍射、扫描电子显微镜手段对样品进行表征。以六次甲基四胺为沉淀剂制得的Co3O4,在6 mol.L-1KOH水溶液中,电位窗口为0～0.4V内,通过循环伏安和恒流充放电测试,显示该材料制备的电极具有良好的电容行为。充放电流在为5 mA时,单电极的比容量达到239 F.g-1,是以碳酸氢铵为沉淀剂制得的Co3O4电极的1.57倍,说明以六次甲基四胺为沉淀剂制备的Co3O4具有较好的电化学电容性能。     

Effect of silver oxide doping on surface and catalytic properties of Co3O4/Al2O3 system

Cobaltic oxide catalyst supported on gamma-alumina having the formula 0.1 Co₃O₄/Al₂O₃ was prepared by wet impregnation method using finely powdered Al(OH)₃ and cobalt nitrate dissolved in the least amount of distilled water. Four silver oxide-doped samples were prepared by impregnating Al(OH)₃ solid with calculated amounts of silver nitrate dissolved also in the least amount of distilled water prior to impregnation with cobalt nitrate solution. The amounts of Ag₂O were 0.2, 0.4, 0.8 and 1.6 wt.%. Pure and doped solids were subjected to heat treatment at 400, 600 and 800 °C. Diffraction lines of Co₃O₄ phase were detected in the XRD patterns of pure and doped solids precalcined at different temperatures. However, the doping process conducted at different temperatures brought about a progressive significant increase in the particle size and degree of ordering of Co₃O₄ phase. Ag₂O-doping of the investigated system affected a measurable decrease in its specific surface areas. The catalytic activities of different solids, in CO-oxidation by O₂ conducted at 125–225 °C, were found to increase significantly by increasing the amount of dopant added reaching to a maximum limit at 0.8 wt.% Ag₂O. The maximum increase in the catalytic activity expressed as reaction rate constant k measured at 150 °C over the solids precalcined at 400 °C and at 175 °C for the solids precalcined at 600 and 800 °C attained 337%, 118% and 219%, respectively. The doping process did not modify the activation energy (E_a) of the catalyzed reaction, and the observed apparent changes in E_a values resulted from a compensation effect as evidenced from almost same changes in the values of pre-exponential factor of Arrhenius equation. Therefore, the observed increase in the catalytic activity of the investigated system due to Ag₂O treatment, which did not change the mechanism of the catalyzed reaction, could be attributed to an effective increase in the concentration of active sites contributing in chemisorption and catalysis of CO oxidation by O₂.     

A novel mild route to hausmannite Mn3O4 nanocubes at room temperature and its catalytic performance

Mn₃O₄ nanocubes were prepared by a modified autoxidation of the slurry, obtained by the reaction of manganese acetate and sodium tetraborate at room temperature. The Mn₃O₄ products were investigated by X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), transmission electron microscopy (TEM), etc. The results indicate that the as-synthesized products have good crystallization and Mn₃O₄ nanocubes with the dimensions of about 100 nm. The catalytic test shows that Mn₃O₄ nanocubes exhibit good catalytic performance in the oxidation of carbon monoxide. Almost 100% oxidization of carbon monoxide to carbon dioxide for the second and third runs is nearly the same to that of the first one, revealing the excellent thermal stability and recycling performance of the Mn₃O₄ nanocubes as catalyst.