Kinetics of oxidation of phenol with manganese dioxide

The kinetics of oxidation of phenol with manganese dioxide at pH 5.5±0.5 were studied. In the temperature range from 393 to 323 K the reaction is of second order, and it occurs in the kinetic mode with an energy of activation of 42.0 kJ/mol. In the temperature range from 333 to 353 K the reaction follows first-order equation and is controlled by external diffusion; the energy of activation is equal to 6.65 kJ/mol. The oxidation products are hydroquinone and 1,4-benzoquinone, the fraction of the latter being less than 10 mol %.     

Lithium manganese oxide with excellent electrochemical performance prepared from chemical manganese dioxide for lithium ion batteries

Chemical manganese dioxide (CMD) is synthesized by the SEDEMA process and adopted as a precursor for lithium manganese oxide with a spinel structure (LMO). LMO is also prepared from electrolytic manganese dioxide (EMD) as a reference for comparison. X-ray diffraction (XRD) shows that CMD is composed of γ-MnO₂, and scanning electron microscopy (SEM) with transmission electron microscopy (TEM) shows that the nanorods cover a spherical core with a diameter < 1 μm. The LMO prepared from CMD shows a much better rate capability and cycle life performance than that from EMD at high temperatures and high current densities. The excellent electrochemical performance is attributed to the structural stability during charge and discharge and the morphology of the LMO, a loose aggregation of the octahedral particles with a uniform size (<1 μm) and shape, which originated from that of CMD.     

Influence of manganese dioxide on the oxidation states of plutonium

When manganese dioxide impregnated filters have been used to concentrate plutonium from water solutions some anomalies were detected, which were ascribed to the probable existence of plutonium in two different oxidation states. The results of this paper seem to confirm this assumption that the Pu in the solution is a mixture of Pu(III) and Pu(IV). After contact with MnO₂, plutonium in the solution consists of only Pu(IV).     

N-羟基邻苯二甲酰亚胺和二氧化锰高效催化对硝基甲苯氧化

采用N-羟基邻苯二甲酰亚胺(NHPI)和二氧化锰(MnO2)作为催化剂催化对硝基甲苯的氧化反应以制备对硝基苯甲酸;对反应条件进行了优化.结果表明,采用10%(与原料的摩尔比)NHPI和10%(与原料的摩尔比)MnO2作为催化剂,在110℃、氧气压力0.4 MPa下反应4 h,对硝基甲苯的转化率为97%,对硝基苯甲酸的分...     

Development of stable PtRu catalyst coated with manganese dioxide for electrocatalytic oxidation of methanol

Manganese dioxide was coated on multiwall carbon nanotubes-supported PtRu particles to prepare the MnO₂/PtRu/CNT catalyst by a facile oxidation–reduction method. The prepared catalyst showed a high stability for electrocatalytic oxidation of methanol. After 2000 potential cycles, 55% activity still remained for MnO₂/PtRu/CNT catalyst, while only 30% activity remained for PtRu/CNT, which indicated that the electrochemical stability of MnO₂/PtRu/CNTs was improved significantly. MnO₂ in MnO₂/PtRu/CNTs prevented the dissolution of PtRu particles as well as the corrosion of the CNT supports, resulting in the improvement of the stability and activity.     

Thermally stable multicomponent manganese catalyst for the deep oxidation of methane to CO2

A thermally stable manganese oxide catalyst for the deep oxidation of lean CH₄ mixtures with air to CO₂ was developed and characterized. To prepare this catalyst, new approaches to the synthesis of polyoxide catalysts based on Mn modified with La, Ce, Ba, and Sr by supporting them from nitrate solutions onto alumina granules stabilized with 2% Ce were used. The catalyst gave the degree of CH₄ oxidation to CO₂ at a level of 90–98% at a CH₄ concentration of 0.2–4.0% in air (space velocity of 10 × 10³ h^?1; temperature of 973 K). The heating of a Mn-containing sample in air to 1373 K had no negative effect on the conversion of CH₄; an insignificant decrease in the catalyst activity (by ～10%) was observed only on heating above 1473 K. The degree of CH₄ oxidation to CO₂ depended only slightly on O₂ and CH₄ concentrations varied over the ranges 2–20 and 0.5–4.0%, respectively. With the use of physicochemical techniques (XRD analysis, BET, electronic diffuse-reflectance spectroscopy, TPD, TPR, and TPO), it was found that the catalyst underwent considerable phase transformations as the temperature was increased to 1473 K: Mn₂O₃ clusters, which occurred at 873 K, were partially converted into LaMnO₃ perovskites above 1173 K or LaMnAl₁₁O₁₉ hexaaluminates above 1273 K. Oxygen that is the constituent of the latter species participated in the oxidation of CH₄ to CO₂.     

Poisoning of typical catalysts of complete oxidation by sulfur dioxide in CO oxidation. Methodical aspects

A method has been proposed for the study of the stability of typical catalysts for complete oxidation with respect to poisoning by sulfur dioxide in CO oxidation.

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CO.

     

Permanganate oxidation of glycine: Influence of amino acid on colloidal manganese dioxide

Permanganate ion oxidizes glycine in phosphate buffered solutions, and the product obtained was identified as a soluble form of colloidal manganese dioxide. The influence of glycine on the colloidal product shows glycine concentration changes extinction coefficients of the colloidal product, and only when the influence of glycine has been eliminated, the theoretical and experimental reaction rates coincide. The dependence of the rate of flocculation on several experimental variables was also considered.     

Electrode reactions of manganese oxides for secondary lithium batteries

Nanorods of MnO₂, Mn₃O₄, Mn₂O₃ and MnO are synthesized by hydrothermal reactions and subsequent annealing. It is shown that though different oxides experience distinct phase transition processes in the initial discharge, metallic Mn and Li₂O are the end products of discharge, while MnO is the end product of recharge for all these oxides between 0.0 and 3.0 V vs. Li⁺/Li. Of these 4 manganese oxides, MnO is believed the most promising anode material for lithium ion batteries while MnO₂ is the most promising cathode material for secondary lithium batteries.     

过渡金属氧化物掺杂对铜锰氧化物催化CO氧化性能的影响

以乙酸铜和乙酸锰为铜锰前驱体,以NH₄HCO₃为沉淀剂,相应金属硝酸盐为掺杂剂,采用共沉淀法制备了不同过渡金属氧化物掺杂的铜锰氧化物催化剂.?采用N₂物理吸附、X射线衍射,氢气-程序升温还原和原位红外漫反射光谱等方法对催化剂进行了表征,考察了系列催化剂上CO反应性能.?结果表明,掺杂过渡金属氧化物可以调变催化剂对CO的吸附能力,进而影响催化剂性能.     

Nb-doped rutile titanium dioxide nanorods for lithium-ion batteries

Rutile titanium dioxide is a promising negative electrode material for lithium-ion batteries due to low volume change on lithium-ion insertion, fast ion diffusion, and large surface area. However, the low theoretical capacity and conductivity of titanium dioxide has limited its application. In this work, rutile TiO₂ was synthesized using a batch hydrothermal method, and doped with Nb⁵⁺ (3.5 at%). <Potentiodynamic/galvanostatic > cycling in the range 1.0–3.0 V vs Li/Li⁺ was used to determine the Li-ion capacity of the doped and pristine TiO₂ material, and electrochemical cycling was used to measure the extent of conversion from the lithiated to de-lithiated state. The nanoscale structures of the pristine and doped materials were determined by powder X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller surface area measurements. Cycling in the range 1.0–3.0 V vs Li/Li⁺ showed that Nb⁵⁺ doping into the structure resulted in higher charge capacities. After 100 cycles at 100 mA g⁻¹, the Nb-doped rutile TiO₂ maintained a capacity of ca. 390 mAh g⁻¹, 64% higher than undoped TiO₂. For electrochemical cycling in the range 0.05–3.0 V vs Li/Li⁺, the introduction of Nb⁵⁺ resulted in a higher conversion of rutile TiO₂ from the lithiated to de-lithiated state. The higher capacity of the doped TiO₂ is shown to be mainly due to the smaller particle size, optimized surface area, and orientation of the nanorods.     

Kinetics and mechanism of oxidation of malonic acid by permanganate and manganese dioxide in acid perchlorate medium

Summary The kinetics of oxidation of malonic acid by both [MnO₄]^– and MnO₂ have been studied in an HClO₄ medium. The oxidation product of the organic acid was found to be glyoxylic acid. A reaction mechanism assuming complexation between MnO₂ and malonic acid is suggested. The rate is independent of [H⁺].     

Ultrafine manganese dioxide nanowire network for high-performance supercapacitors

Ultrafine MnO(2) nanowires with sub-10 nm diameters have been synthesized by a simple process of hydrothermal treatment with subsequent calcinations to form networks that exhibit an enhanced specific capacitance (279 F g(-1) at 1 A g(-1)), high rate capability (54.5% retention at 20 A g(-1)) and good cycling stability (1.7% loss after 1000 cycles).     

A Study of Structure and Catalytic Activity of Ag-Fe Mixed Oxide Catalysts for CO oxidation

Much effort is made to reduce CO to environment pollution^[1]. The precious metal (such as Pt, Pd, Rh) are well known to apply in the total oxidation to treat with the exhaust gas emission and CO, which have good situation in high activity and stability^[2]. Due to the high cost and limited availability of precious metal, people become more and more interested in searching base metals to replace precious metal, especially,transition metal oxide catalysts. In our study, the results indicate that the Ag/Fe (1:1) catalyst exhibits highest active to CO oxidation. It is detected that the highly dispersed state of σ-AgFeO₂ is the active site for CO oxidation.     

Reduction of colloidal manganese dioxide by manganese(II)

The reduction of colloidal MnO(2) by Mn(2+) in aqueous HClO(4) has been studied by a spectrophotometric method. The reaction product is Mn(III). The reaction is of first order in both colloidal MnO(2) and H(+), whereas it presents a fractional order (0.58+/-0.02) in Mn(2+). The reaction is retarded by addition of NaClO(4), but is not affected by addition of tert-butanol. The corresponding activation energy is 29.5+/-1.3 kJ mol(-1). The reaction is catalyzed by Na(4)P(2)O(7), and the pyrophosphate-catalyzed reaction is of first order in both colloidal MnO(2) and pyrophosphate and of fractional order (0.64+/-0.01) in Mn(2+), whereas its rate presents a complex dependence on the concentration of H(+). The pyrophosphate-catalyzed reaction is accelerated by addition of both NaClO(4) and tert-butanol. The corresponding activation energy is 49.7+/-3.0 kJ mol(-1). Mechanisms in agreement with the experimental data are proposed for both the parent and the pyrophosphate-catalyzed reactions.     

Comments on stabilizing layered manganese oxide electrodes for Li batteries

An electrochemical study of structurally-integrated xLi₂MnO₃•(1 −x)LiMn_0.5Ni_0.5O₂ ‘composite’ materials has been undertaken to investigate the stability of electrochemically-activated electrodes at the Li₂MnO₃-rich end of the Li₂MnO₃–LiMn_0.5Ni_0.5O₂ tie-line, i.e., for 0.7 ≤ x ≤ 0.95. Excellent performance was observed for x = 0.7 in lithium half-cells; comparable to activated electrodes that have significantly lower values of x and are traditionally the preferred materials of choice. Electrodes with higher manganese content (x ≥ 0.8) showed significantly reduced performance. Implications for stabilizing low-cost, manganese-rich, layered lithium-metal-oxide electrode materials are discussed.     

Effect of fractal dimension of zirconium dioxide on its catalytic properties in the oxidation of CO

The effect of fractal dimension of zirconium dioxide on its catalytic properties in the oxidation of CO has been studied. The interconnection between the pre-exponential factor of the reaction rate constant and the fractal dimension of the catalyst has been established. It has been shown that the pre-exponential factor decreases with an increase in the mass fractal dimension.     

Anomalies in thorium adsorption on manganese dioxide

In this paper the authors present a study of the adsorption of thorium on manganese dioxide by batch equilibration and cartridge experiments. Some anomalies in the use of MnO₂ to concentrate thorium have been found. So the use of this technique is limited for the determination of thorium in natural waters.