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Pillared layered manganese oxide

Synthesis and redox properties

Journal of Thermal Analysis and Calorimetry
Authors: She-Tin Wong and Soofin Cheng

Abstract  

Keggin ion-pillared buserite was prepared by ion-exchanging the hexylammonium ion-expanded buserite with Keggin ions, [Al13O4(OH)24(H2O)12]7+. The starting material was synthetic Na-buserite, which is a layered manganese oxide of composition Na4Mn14O26 xH2O. The thermal and redox properties of this oxide and its pillared derivative were compared in O2, N2 and H2 environments using TG, DSC and XRD. The results indicated an improvement in thermal stability of pillared compound relative to Na-buserite in all gaseous environments. By using these compounds in catalysing the oxidation of ethane, it was found that they were very active for complete oxidation.

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Journal of Thermal Analysis and Calorimetry
Authors: C. González, J. I Gutiérrez, J. R. González-Velasco, A. Cid, A. Arranz, and J. F. Arranz

Thermal decomposition of various synthetic manganese oxides (MnO, Mn3O4, Mn2O3, MnOOH) and a natural manganese dioxide (MnO2) from Gabon was studied with the help of termogravimetry in inert, oxidizing and reducing atmospheres. The compounds were characterized by XRD and electrochemical activity was tested by cyclic voltammetry using a carbon paste electrode. The natural manganese dioxide showed the best oxidizing and reducing capacity, confirmed by the lower temperatures of the transitions, the extent of the reactions and electrochemical performance in cyclic voltammograms.

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Abstract  

The course of reactions of potassium disulphate(VI) with manganese oxides: MnO, Mn2O3 and MnO2 was studied in solid phase. In the reactions all the manganese oxides were reduced to Mn2+ which then became a component of one of the reaction products namely K2Mn2(SO4)3. A classification scheme of the reaction path has been proposed.

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Abstract  

Manganese oxide samples obtained from thermal decomposition of manganese carbonate at 400 and 600 °C were subjected to different doses of g-irradiation within the range 0.2 to 1.6 MGy. The surface and catalytic properties of the above samples were studied using nitrogen adsorption isotherms measured at -196 °C and catalytic conversion of ethanol and isopropanol at 300-400 °C using micropulse technique. The results obtained revealed that manganese oxides obtained at 400 °C consisted of a mixture of Mn2O3 and MnO2 while the samples calcined at 600 °C composed entirely of Mn2O3. Gamma-irradiation resulted in a decrease in the particle size of manganese oxide phases with subsequent increase in their specific surface areas. Gamma-irradiation with 0.2 and 0.8 MGy effected a measurable progressive decrease in the catalytic activity in dehydration and dehydrogenation of both alcohols. However, the treated catalyst retained their initial activity upon exposure to a dose of 1.6 MGy. Also, g-irradiation increased the selectivities of the investigated solids towards dehydrogenation of both alcohols. The catalyst samples precalcined at 600 °C exhibited higher catalytic activities than those precalcined at 400 °C.

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Abstract  

In this paper, the sorption properties of manganese oxide coated sand (MOCS) towards uranium(VI) from aqueous solutions were studied in a batch adsorption system. Scanning electron microscope (SEM) and infrared (IR) analyses were used to characterize MOCS. Parameters affecting the adsorption of uranium(VI), such as the contact time, salt concentration, competitive ions, temperature and initial uranium(VI) concentration, were investigated. The equilibrium adsorption data were analyzed by Langmuir, Freundlich and Redlich–Peterson models using nonlinear regressive analysis. The results indicated that the Langmuir and Redlich–Peterson models provided the best correlation of experimental data. The kinetic experimental data were analyzed using three kinetic equations including pseudo-first order equation, pseudo-second order equation and intraparticle diffusion model to examine the mechanism of adsorption and potential rate-controlling step. The process mechanism was found to be complex, consisting of both surface adsorption and pore diffusion. The effective diffusion parameter D i values estimated in the order of 10−7 cm2 s−1 indicated that the intraparticle diffusion was not the rate-controlling step. Thermodynamic study showed that the adsorption was a spontaneous, endothermic process. Adsorbed U(VI) ions were desorbed effectively (about 94.7%) by 0.1 mol L−1 HNO3. The results indicated that MOCS can be used as an effective adsorbent for the treatment of industrial wastewaters contaminated with U(VI) ions.

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TiO 2 , and little was done about Mn oxide. To the best of our knowledge, few reports have been published on the characterization of boron-doped manganese oxide and its photocatalytic activity in aniline degradation. Aniline is known to be one

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Abstract  

The kinetics of the exchange between56Mn-labelled manganese dioxide and cations in aqueous solution was studied by measuring the β activity acquired by the solution. The results of the exchange between a chemical γ MnO2 and a divalent M2+ ion (M=Mn, Co, Cu or Zn) or a trivalent M3+ ion (M=Ga, Fe, In, Rh or Al) indicate a fast initial process followed by a diffusion—controlled exchange. It is assumed that M2+ ions exchange with Mn2+ ions and M3+ ions exchange with Mn3+ ions in MnO2. The process depends on the radii of the host and substituent ions and on consideration of crystal field stabilisation energies. It seems that the γ MnO2 studied contains more Mn3+ than Mn2+ ions. The possibility of the exchange between Mn ions and cations of a different charge cannot be ruled out. The exchange between Co2+ ions and MnO2 was enhanced in presence of pyrophosphate, which stabilises Mn(III) as a complex. The fraction of Mn in different samples of MnO2 exchanged with a given cation depends on the type and not on the surface area of the sample.

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Abstract  

Materials with high surface areas and small particle size (nanophases), metastable polymorphs, and hydrated oxides are increasingly important in both materials and environmental science. Using modifications of oxide melt solution calorimetry, we have developed techniques to study the energetics of such oxides and oxyhydroxides, and to separate the effects of polymorphism, chemical variation, high surface area, and hydration. Several generalizations begin to emerge from these studies. The energy differences among different polymorphs (e.g., various zeolite frameworks, the - and -alumina polymorphs, manganese and iron oxides and oxyhydroxides) tend to be small, often barely more than thermal energy under conditions of synthesis. Much larger contributions to the energetics come from oxidation-reduction reactions and charge-coupled substitutions involving the ions of basic oxides (e.g., K and Ba). The thermodynamics of hydration involve closely balanced negative enthalpies and negative entropies and are very dependent on the particular framework and cage or tunnel geometry.

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