Pure Manganese Oxide Research Articles

Reduction of Manganese Oxides by Methane-containing Gas

The paper presents results of reduction of pure manganese oxides by methane containing gas in non-isothermal and isothermal experiments and reduction mechanisms. The extent and rate of manganese oxide reduction were determined by on-line off-gas analysis using a mass-spectrometer in a fixed bed laboratory reactor in the temperature range 1000-1200°C at different gas compositions.Manganese oxides were reduced to carbide Mn7C3. High extent and rate of reduction by methane-containing gas in comparison with carbothermal reduction were attributed to high carbon activity in the reducing gas, which was in the range 15-50 (relative to graphite). The rate of reduction of manganese oxide increased with increasing temperature. Increasing methane content in the reducing gas to 10-20 vol% CH4 favoured the reduction process. Increase in hydrogen partial pressure had a positive effect on the reduction rate. Addition of carbon monoxide to the reducing gas retarded the reduction process. The addition of Fe3O4 to manganese oxide increased the rate of reduction.Reduction by methane-containing gas occurs through adsorption and cracking of methane with formation of active adsorbed carbon. Deposition of solid carbon retarded the reduction.

Structural and morphological characterization of Mn–Zr mixed oxides prepared by a sol–gel method

Abstract Mn–Zr mixed oxide materials have been prepared by a sol–gel method from a Mn (III) precursor salt and a solution of zirconium acetate in acetic acid, being characterized from a structural and morphological point of view. Conventional solid state techniques show that as obtained powders are formed by mixtures of manganese and zirconium acetates and (hydro) oxides, which evolve to bixbyite, hausmannite, as well as tetragonal and monoclinic zirconia above 873 K. Zirconium enhances the formation of the non-thermodynamically stable manganese compounds instead of the thermodynamically stable ones. This effect was not observed in other samples previously prepared by coprecipitation. In general, mixed systems are thermally stable up to 1073 K due to the formation of a solid solution phase of 10% Mn into zirconia, and display higher specific surface areas than those prepared by the coprecipitation method. Their activities in the combustion of heavy aromatic molecules are higher than those of the pure manganese oxides, very likely due to a synergic effect of zirconium. Moreover, the catalytic properties of hausmannite and bixbyite phases for burning this type of hydrocarbons seem to be very similar.

Solid–solid interaction between ferric oxide and manganese carbonate as influenced by lithium oxide doping

The solid–solid interaction between pure and lithia-doped manganese and ferric oxides have been investigated using DTA and XRD techniques. Equimolar proportions of manganese carbonate and ferric oxide were employed, while the dopant substrate was added as lithium nitrate. The amounts of dopant were 0.89, 1.68 and 3.36 mol% Li 2O. The results obtained revealed that the thermal treatment of manganese carbonate and ferric oxide at 800°C resulted in the formation of Mn 2O 3 (Partridgeite) and α-Fe 2O 3 phases having an excellent degree of crystallinity. Solid–solid interaction took place between the produced oxides at temperatures starting from 900°C yielding MnFe 2O 4 (Jacobsite). The degree of propagation of this reaction was found to increase by increasing both the precalcination temperature and the amount of Li 2O added. The progressive increase in the height of the diffraction line of MnFe 2O 4 at “d” spacing of 2.56 Å (100%) as a function of precalcination temperature for pure and variously doped mixed solids was utilized in the determination of activation energy of formation of manganese ferrite (Δ E). The computed Δ E values were 174, 153, 134 and 117 kJ mol −1 for pure mixed solids and those doped with 0.84, 1.68 and 3.36 mol% Li 2O. These results were discussed in terms of dissolution of lithium cations in the lattices of Fe 2O 3 and Mn 2O 3 solids with subsequent increase in the mobility of the reacting ferric and manganese cations.

Solution Synthesis and Characterization of Lithium Manganese Oxide Cathode Materials

ABSTRACTA nonaqueous coprecipitation process has been developed to prepare controlled stoichiometry lithium manganese oxalate precipitates. The process involved mixing a methanolic Li-Mn nitrate solution with a methanolic solution containing tetramethylammonium oxalate as the precipitating agent. The resulting oxalates were readily converted to a variety of phase pure lithium manganese oxides at moderate temperatures (≤600°C), where the phase formed was determined by the initial Li/Mn ratio in the starting solution. Metal cation dopants have been incorporated into the oxalate precipitate by dissolving the appropriate metal nitrate in the Li-Mn precursor solution The various starting solutions, oxalate precipitates, and calcined oxides have been extensively characterized using a variety of techniques, including 7Li NMR, TGA/DTA, SEM, and XRD. Results indicate that a strong interaction occurs between Li and Mn in the nitrate solution which carries over into the oxalate phase during precipitation. The morphology and the crystallite size of the oxide powders were shown to be controlled by the morphology of the oxalate precursor and the oxalate calcination temperature, respectively. The results of initial cathode performance tests with respect to dopant type (Al, Ni, Co) and concentration for LiMn2O4 are also reported.

ChemInform Abstract: Activity and Selectivity of Pure Manganese Oxides in the Selective Catalytic Reduction of Nitric Oxide with Ammonia.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Activity and selectivity of pure manganese oxides in the selective catalytic reduction of nitric oxide with ammonia

Manganese oxides of different crystallinity, oxidation state and specific surface area have been used in the selective catalytic reduction (SCR) of nitric oxide with ammonia between 385 and 575 K. MnO 2 appears to exhibit the highest activity per unit surface area, followed by Mn 5O 8, Mn 2O 3, Mn 3O 4 and MnO, in that order. This SCR activity correlates with the onset of reduction in temperature-programmed reduction (TPR) experiments, indicating a relation between the SCR process and active surface oxygen. Mn 2O 3 is preferred in SCR since its selectivity towards nitrogen formation during this process is the highest. In all cases the selectivity decreases with increasing temperature. The oxidation state of the manganese, the crystallinity and the specific surface area are decisive for the performance of the oxides. The specific surface area correlates well with the nitric oxide reduction activity. The nitrous oxide originates from a reaction between nitric oxide and ammonia below 475 K and from oxidation of ammonia at higher temperatures, proven by using 15NH 3. Participation of the bulk oxygen of the manganese oxides can be excluded, since TPR reveals that the bulk oxidation state remains unchanged during SCR, except for MnO, which is transformed into Mn 3O 4 under the applied conditions. In the oxidation of ammonia the degree of oxidation of the nitrogen containing products (N 2, N 2O, NO) increases with increasing temperature and with increasing oxidation state of the manganese. A reaction model is proposed to account for the observed phenomena.

A growing deposit of hydrous manganese oxide produced by microbial mediation at a hot spring, Japan.

The formation process of hydrous manganese oxide deposit can hardly be demonstrated in natural environments, namely, hot and cold springs and deep-sea hydrothermal vents. We discovered a unique phenomenum that hydrous manganese oxide is now actively depositing from the hot spring water at the Yuno-taki Falls, Hokkaido, Japan. The chemical and the biological factors that potentially control the actual manganese deposition in the natural environment were examined. Pure manganese oxide deposit (1.1 ton/year calculated as MnO2) is currently being formed from weakly acidic hot spring water by the mediation of microbial consortium consisting of manganese-oxidizing bacteria and filamentous algae. A comparison of the mineral deposition at this location with other terrestrial and oceanic deposits suggests that they were formed in a similar manner.

Decomposition of hydrogen peroxide over pure and mixed copper oxide and manganese oxide prepared from carbonates

Thermal decomposition of püre and mixed copper and manganese carbonate 1.0: 0.225, 1.0: 0.50 and 1.0: 1.0 with respect to CuO: MnO2 was studied. The products at different tem- peratures were characterized by x-ray diffraction analysis. The catalytic activity of the thermal products of püre and mixed oxides was tested in H2O2 decomposition. Thermal treatment of copper carbonate produced CuO at temperature as low as 200°C the increase of temperature of treatment increased the degree of crystallinity of CuO. Manganese carbonate starts to decompose at temperatures higher than 300°C yielding MnO2 whereas at 500°C a mixture of cubic and tetragonal Mn2O3 was detected. At temperatures higher than 500°C, the majör crystalline form of Mn2O3 was cubic. On the other hand, Cu-Mn-mixed carbonates produced only MnC03 crystalline form at low temperatures. At 500°C CuO and other compounds such as Mn2O3 or CuMn2O4 were detected depending on the composition of mixtures. The increase of temperature of treatment was found to be accompanied by an increase in the degree of crystallinity of CuMn2O4. The catalytic activity of these solids in hydrogen peroxide decomposition was found to increase as the activation temperature was increased passing through a maximum when the cata- lysts were preheated at 500°C. The increase of calcination temperature higher than 500°C was accompanined by a marked decrease in the activity in H2O2 decomposition. This may be attri- buted to sintering and / or formation of inactive form of CuMn204.

Secondary Li cells. I. A comparison of the behaviour of cathodes based on pure and lithiated manganese oxides

In an attempt to better understand the rechargeability of some MnO 2-based cathodes in Li cells, an investigation on some pure MnO 2 (CMD and EMD) and LiMnO phases has been carried out. It has been found that all forms of pure MnO 2 investigated are inherently reversible, but with different kinetic limitations. Faradiser WS Li (CMD) shows an excellent cycling behaviour provided it is not heat-transformed into a β phase. Spinel-like compounds and Li-birnessite (a layered phase) do not perform as well as the best CMD's. The products of the reactions of CMD or EMD with LiNO 3 or LiOH have been examined. As a function of the synthesis conditions, phases predominantly containing Li x MnO 2 or phases with consistent amounts of spinels and Li 2MnO 3 can be obtained. A product formed from HNO 3-treated CMD and LiNO 3 (7 : 3 molar ratio) at 370°C shows an especially satisfactory cycling behaviour.

Thermodynamics of iron manganese mixed oxides at high temperatures

The deviation from stoichiometry in dense polycrystalline (Fe 1− x Mn x ) 1−ΔO has been investigated thermogravimetrically as a function of the oxygen partial pressure and the crystal composition at T = 1000°C over the whole range of stability of this phase. The phase diagram of the system Fe-Mn-O at T = 1000°C has been reinvestigated. In addition, the two-phase regions and the activities of the pure iron and manganese oxides in the mixed phases (Fe, Mn)O and (Fe, Mn) 3O 4 have been calculated.

Fe/Mn Oxide Catalysts for Fischer‐Tropsch Synthesis Part VIII: Surface Characterization of Fe/Mn‐Fischer‐Tropsch Catalysts by Auger‐Electron‐Spectroscopy

AbstractSurface compositions of Fe/Mn‐oxide Fischer‐Tropsch catalysts were determined by AES. Bulk compositions of the samples varied from pure iron oxide to pure manganese oxide. A method for quantification of Auger spectra was developed. The iron content in the surfaces of the samples after calcination and reduction is larger than in the bulk. The surface composition after FT synthesis depends on the temperature of reduction before synthesis. The results of surface analysis of the calcined and reduced samples are compared with those of adsorption measurements described elsewhere.

Fe/Mn Oxide Catalysts for Fischer‐Tropsch‐Synthesis Part VII: Adsorption of Carbon Monoxide and Nitrogen at Low Temperatures

AbstractIron/manganese oxides often used as catalysts for the Fischer‐Tropsch (FT) hydrogenation of CO have been characterized by their adsorption properties. N2 physisorption was carried out at 77 K and CO chemisorption at 194 K in a vacuum microbalance. Precipitated solids with compositions ranging from pure iron oxide to pure manganese oxide were studied after calcination and reduction. The results indicate a correlation between the fraction of metallic iron in the surface, the irreversible chemisorption of CO at 194 K and the initial activity for FT synthesis.

The activities of manganese nodules and manganese-iron mixed oxide for decomposition of isopropyl alcohol

Mn-N collected from the ocean floor contained 14Vertical Bar3< Mn, 12.91Vertical Bar3< Fe, 18.57Vertical Bar3< acid insolubles (silica and aluminosilicate), and Vertical Bar3; 0.5Vertical Bar3< each of cobalt, nickel, copper, and other impurities. They were crushed, calcined at 200/sup 0/-600/sup 0/C, and tested for the conversion of isopropanol in helium. The surface area of Mn-N calcined at 200/sup 0/-300/sup 0/C was approx. 300 sq m/g, and it decreased at higher calcination temperatures. Maximum conversion was obtained on the Mn-N calcined at 400/sup 0/C, which gave acetone with approx. 75Vertical Bar3< selectivity at approx. 60Vertical Bar3< conversion, and carbon dioxide. The conversion and selectivity pattern was similar for pure precipitated manganese oxide, and it differed for pure precipitated iron oxide by forming propylene instead of carbon dioxide as the minor product. The surface areas of these pure metal oxides were much smaller than that of Mn-N. Precipitated manganese-iron mixtures with the appropriate metal additives duplicated the activity and surface area of the Mn-N. The oxidation process which produced carbon dioxide and water probably used excess surface oxygen of the catalyst.

Thermal Decomposition ofKClO4Catalyzed with Pure and Doped Manganese Oxide Catalysts

Thermal Decomposition of<i>KClO</i>₄Catalyzed with Pure and Doped Manganese Oxide Catalysts

The mineralogy and chemistry of manganese in some Australian soils

The mineralogical and chemical compositions of 28 manganese nodules from Australian soils were studied. Specific manganese minerals were identified in 26 of these after extraction and concentration from the associated soil minerals; 10 were lithiophorite Li2A18 (Mn2+, Co, Ni)2, Mn4+10O35.14H2O; 10 were birnessite, (Ca, Mg, Na2, K2)x Mn4+Mn2+(O, OH)2; 3 were hollandite, Ba(Mn4+, Fe3+)8O16; 1 was todorokite (Mn2+, Mg, Ca)Mn4+6O13.3-4H2O; 1 was pyrolusite MnO2; 1 contained both lithiophorite and hollandite. With the possible exception of pyrolusite, all samples were found to contain varying amounts of Ni, Co, Mg, Ba, Al, K, Na, Fe, and Ca. Although there was overlap in the chemistry of the birnessite and lithiophorite groups, the mean concentrations of aluminium, iron, and lithium were lower and the mean concentration of calcium and magnesium higher in the former group. Pure manganese oxides and hydroxides appear to be quite rare as secondary soil minerals. Lithiophorite occurred mainly in neutral to acid subsurface soils, whereas birnessite, although found in both acid and alkaline soils, was more common in alkaline surface horizons. The average crystallite size of the manganese mineral aggregates was quite small, being of the order of 0.02 �m for birnessites and 0.1 �m for the lithiophorites.