Thermal Decomposition of Manganese Carbonate Supported on Active Alumina

The effect of aluminium oxide support on the thermal behaviour of manganese carbonate was investigated using TG, DTA, dDTA and XRD techniques. The concentrations of MnCO₃ were 0.025, 0.05 and 0.125 mol/mol Al₂O₃. The results obtained showed that the employed support material retards the thermal decomposition of manganese carbonate due to the formation of a manganese/aluminium adduct which decomposes readily at 350°C instead of 250°C in the absence of Al₂O₃, to give γ-MnO₂. This compound decomposed at 500°C into Mn₂O₃ (partridgeite). The produced Mn₂O₃ decomposed at 940°C yielding Mn₃O₄ which interacted with atmospheric oxygen during the cooling processes to give Mn₂O₃. However, Mn₃O₄ formed in the case of unloaded Mn₂O₃ did not interact easily with O₂ and remained stable. The results might indicate the role of Al₂O₃ in increasing the degree of dispersion of the produced manganese oxides thus increasing their reactivity towards reoxidation by O₂. The produced manganese oxide (Mn₂O₃) enhanced markedly the crystallization of aluminium oxide at 800°C into ?-Al₂O₃. Solid-solid interaction between Mn₂O₃ and Al₂O₃ occurred at 800°C giving MnAl₂O₄ which decomposed at 1000°C yielding Mn₂O₃ and α-Al₂O₃ (corundum).     

Effect of γ-irradiation and doping with MoO3 and V2O5 on surface and catalytic properties of manganese oxides

The effects of γ-irradiation (0.2–1.6 MGy), thermal treatment and doping with MoO₃ and V₂O₅ (0.25–4 mol%) on the surface and catalytic properties of manganese oxides prepared by thermal decomposition of manganese carbonate at 400°C and 600°C have been investigated. The techniques employed were X-ray diffraction, nitrogen adsorption at −196°C, oxidation of CO by O₂ at 120–220°C and decomposition of H₂O₂ at 20–50°C. The results revealed that γ-irradiation decreased the particle size of manganese oxides, increased their specific surface areas, decreased the amount of surface excess oxygen and decreased their catalytic activities. The doping with MoO₃ and V₂O₅ conducted at 600°C brought about a measurable decrease in the BET-surface area and catalytic activities of the treated solids. These results were discussed in terms of splitting of manganese oxide particles and removal of chemisorbed oxygen by treating with γ-irradiation and formation of manganese molybdate and vanadates by treating with the used dopant oxides.     

Thermal and X-ray diffraction studies of the solid–solid interactions in CuO–MoO3/MgO system

The solid–solid interactions in pure and MoO₃-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO₃ were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000°C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO₃ at temperatures starting from 400°C yielding CuMoO₄ which remained stable up to 1000°C. The other portion of MoO₃ interacted with MgO producing MgMoO₄ at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of Cu₂MgO₃ phase were detected in the diffractograms of pure and MoO₃-doped 0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied by an endothermic peak at 930°C.     

Thermal Characterization and Physico-Chemical Properties of Fe2O3−Mn2O3/Al2O3 Systems

The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al₂O₃ and Fe₂O₃/Al₂O₃ systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe₂O₃ at 350°C and shows thermal stability up to1000°C. Crystalline Fe₃O₄ and Mn₃O₄phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al₂O₃ phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al₂O₃ phase at1000°C. Crystalline MnAl₂O₄ and MnFe₂O₄ phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products was tested using the decomposition of H₂O₂ reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Studies on the formation of manganese molybdate

The reaction of MoO₃ with various oxides of manganese (MnO, Mn₂O₃, Mn₃O₄ and MnO₂) and with MnCO₃ has been studied in air and nitrogen atmospheres employing DTA, TG and X-ray diffraction methods, with a view to elucidating the conditions for the formation of MnMoO₄. Thermal decomposition of MnCO₃ has also been studied in air and nitrogen atmospheres to help understand the mechanism of the reaction between MnCO₃ and MoO₃. The studies reveal that, whereas MnO, Mn₂O₃ and MnO₂ react smoothly with MoO₃ to form MnMoO₄, Mn₃O₄ does not react with MoO₃ in the temperature range investigated (48O–6OO°C). An equimolar mixture of MnCO₃ and MoO₃ reacts in air to yield MnMoO₄, while only a mixture of Mn₃O₄ and MoO₃ remains as final product when the same reaction is carried out in nitrogen. Marker studies reveal that manganese ions are the main diffusing species in the reaction between MoO₃ and manganese oxides that result in MnMoO₄.     

Thermal decomposition of manganese(II)bis(oxalato)nickelate(II)tetrahydrate

Summary A mixed metal oxalate, manganese(II)bis(oxalato)nickelate(II)tetrahydrate, has been synthesized and characterized by elemental analysis, IR spectral and X-ray powder diffraction (XRD) studies. Thermal decomposition studies (TG, DTG and DTA) in air showed that the compound decomposed mainly to Mn₂O₃, MnO₂ and NiO at ca.1000°C, via. the formation of several intermediates. DSC study in nitrogen upto 500°C showed the endothermic decomposition. The tentative mechanism for the thermal decomposition in air is proposed.     

Effect of the oxidation state of manganese in the manganese oxides used in the synthesis of Mn-substituted cordierite on the properties of the product

Catalysts based on Mn-substituted cordierite 2MnO · 2Al₂O₃ · 5SiO₂ have been synthesized using different manganese oxides (MnO, Mn₂O₃, and MnO₂) at a calcination temperature of 1100°C. The catalysts differ in their physicochemical properties, namely, phase composition (cordierite content and crystallinity), manganese oxide distribution and dispersion, texture, and activity in high-temperature ammonia oxidation. The synthesis involving MnO yields Mn-substituted cordierite with a defective structure, because greater part of the manganese cations is not incorporated in this structure and is encapsulated and the surface contains a small amount of manganese oxides. This catalyst shows the lowest ammonia oxidation activity. The catalysts prepared using Mn₂O₃ or MnO₂ are well-crystallized Mn-substituted cordierite whose surface contains different amounts of manganese oxides differing in their particle size. They ensure a high nitrogen oxides yield in a wide temperature range. The product yield increases with an increasing surface concentration of Mn³⁺ cations. The highest NO_x yield (about 76% at 800–850°C) is observed for the MnO₂-based catalyst, whose surface contains the largest amount of manganese oxides.     

Kinetics and mechanism of the oxidative dehydrogenation of isobutane on cobalt,nickel, and manganese molybdates

The kinetics of oxidative dehydrogenation of isobutane in the presence of atmospheric oxygen on manganese molybdate has been studied. The experiments have been carried out in a circulation flow reactor at 470–530°C. The form of kinetic equations and the mechanism of the formation of isobutene, carbon oxides, and cracking products on manganese molybdate are similar to those found previously for the same reaction on cobalt and nickel molybdates. The highest yields of isobutene and propene (isobutane cracking products) are achieved on Co_0.95MoO₄. The mechanism of the process has been investigated by the unsteady-state response method. Manganese molybdate contains the largest amount of reactive oxygen, whereas nickel molybdate contains the smallest amount of reactive oxygen. The earlier conclusion that molybdate lattice oxygen and chemisorbed oxygen play the main role in the formation of iso-C₄H₈ and in deep oxidation processes, respectively, is confirmed.     

Homogeneity range of neodymium manganite in air

The solubility boundaries for Nd₂O₃ and manganese oxides in NdMnO_{3 ± δ} have been determined by X-ray powder diffraction analysis of homogeneous phases and heterogeneous compositions of the general formula Nd_{2 ? x} Mn _x O_{3 ± δ} (0.90 ≤ x ≤ 1.20; Δx = 0.02) prepared by ceramic technology from constituent oxides in air in the temperature range 900–1400°C. The results are presented in the form of a fragment of the Nd-Mn-O phase diagram in air. It is suggested that the Nd₂O₃ solubility in NdMnO_{3 ± δ} is due to crystal defects and the solubility of manganese oxides is in addition due to the disproportionation reaction 2Mn³⁺ = Mn²⁺ + Mn⁴⁺ and the subsequent partial substitution of divalent for tervalent manganese ions in the cuboctahedral positions of the perovskite-like crystal lattice. To verify this suggestion, it is necessary to systematically study the oxygen nonstoichiometry δ in Nd_{2 ? x} Mn _x O_{3 ± δ} as a function of x and synthesis temperature and structurally study this oxide with these parameters being varied.     

Homogeneity regions of neodymium,samarium, and europium manganites in air

XRD phase analysis of homogeneous phases and heterogeneous compositions of general formula Ln_2?x Mn_xO_3±δ (Ln = Nd, Sm, Eu; 0.90 ≤ x ≤ 1.20; Δx = 0.22) prepared by ceramic synthesis from oxides in air at 900–1400°C was used to determine the solubility boundaries for Ln₂O₃ oxides and maganese oxides in LnMnO_3±δ. The results were represented as fragments of the phase diagrams for the Ln-Mn-O systems in air. It was assumed that the solubility of Ln₂O₃ oxides in LnMnO_3±δ is determined by lattice defects, while that of manganese oxides, in addition to above mechanism, by the disproportionation reaction 2Mn³⁺ = Mn²⁺ + Mn⁴⁺ followed by the partial substitution of divalent magnesium for Ln³⁺ at cuboctahedral positions of the perovskitelike crystal lattice.     

High-Temperature X-Ray Diffraction Investigation of the Decomposition Process in Manganese-Gallium Spinel Mn<Subscript>1.5</Subscript>Ga<Subscript>1.5</Subscript>O<Subscript>4</Subscript>

The stability of spinel-type mixed Mn_1.5Ga_1.5O₄ oxide prepared in an inert medium (1000 °C, Ar) is studied by thermogravimetry and high-temperature X-ray diffraction in air in a wide temperature range 30–1000 °C. On heating, reversible decomposition processes of initial spinel are observed. From 30 °C to 600 °C oxygen atoms attach to the surface layer of initial Mn_1.5Ga_1.5O₄ spinel to form a new phase distinct from parent oxide by the oxygen stoichiometry (cation vacancies are formed). The product of decomposition is two oxides: Mn_1.5Ga_1.5O₄ and Mn_1.5–xGa_1.5–x[·]_xO₄. On the contrary, above 600 °C a loss of oxygen occurs, the concentration of cation vacancies decreases in Mn_1.5–xGa_1.5–x[·]_xO₄, and the reverse process of single phase oxide crystallization takes place. At 1000 °C the spinel phase forms again whose composition is similar to that of the initial parent phase Mn_1.5Ga_1.5O₄. On cooling the decomposition of this phase is again observed due to oxygen attachment.     

Structural characterization and electrochemical intercalation of Li+ in layered Na0.65Ni0.5Mn0.5O2 obtained by freeze-drying method

New data on the structure and reversible lithium intercalation properties of sodium-deficient nickel–manganese oxides are provided. Novel properties of oxides determine their potential for direct use as cathode materials in lithium-ion batteries. The studies are focused on Na _x Ni_0.5Mn_0.5O₂ with x?=?2/3. Between 500 and 700 °C, new layered oxides Na_0.65Ni_0.5Mn_0.5O₂ with P3-type structure are obtained by a simple precursor method that consists in thermal decomposition of mixed sodium–nickel–manganese acetate salts obtained by freeze-drying. The structure, morphology, and oxidation state of nickel and manganese ions of Na_0.65Ni_0.5Mn_0.5O₂ are determined by powder X-ray diffraction, SEM and TEM analysis, and X-ray photoelectron spectroscopy (XPS). The lithium intercalation in Na_0.65Ni_0.5Mn_0.5O₂ is carried out in model two-electrode lithium cells of the type Li|LiPF₆(EC:DMC)|Na_0.65Ni_0.5Mn_0.5O₂. A new structural feature of Na_0.65Ni_0.5Mn_0.5O₂ as compared with well-known O3–NaNi_0.5Mn_0.5O₂ and P2–Na_2/3Ni_1/3Mn_2/3O₂ is the development of layer stacking ensuring prismatic site occupancy for Na⁺ ions with shared face on one side and shared edges on the other side with surrounding Ni/MnO₆ octahedra. The reversible lithium intercalation in Na_0.65Ni_0.5Mn_0.5O₂ is demonstrated and discussed.     

Synthesis,characterization, and x-ray structural study of binary lithium managanese(II) molybdate

The binary molybdate of variable composition Li_2?2nMn_2+x(MoO₄)₃ (O2Fe₂(MoO₄)₃, was discovered in the Li₂MoO₄-MnMoO₄ system. We have grown single crystals of Li_1.60Mn_2.20(MoO₄)₃) and determined its crystal structure (space group Pnma, a=5.145, b=10.681, c=17.985 Å, Z=4). Along with statistical arrangement of Li and Mn in three different atomic positions, cation vacancies in one of these were found. Based on the data obtained, we propose to revise the compositions of some lithium-containing phases with the Li₂Fe₂(MoO₄)₃-type structure.     

Correlation between structure and catalytic activity of manganese oxides in liquid-phase oxidation of 1-octene

We have studied the correlation between the crystal structure and the catalytic activity of manganese oxides MnO, MnO₂, Mn₃O₄, and Mn₂O₃ in liquid-phase oxidation of 1-octene by molecular oxygen. The catalytic activity decreases in the series of oxides with octahedral coordination environment for the manganese atoms MnO−Mn₂O₃−MnO₂. The oxide Mn₃O₄ (with mixed tetrahedral and octahedral environment for the Mn atoms) catalyzes the process according to a different mechanism. L'vov Polytechnic State University, 12 S. Bandery ul., L'vov-13 290646, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 5, pp. 324–327, September–October, 1998.     

Synthesis of nanostructured perovskite powders via simple carbonate co-precipitation

A very simple, cost-effective, chloride- and alkali-free, carbonate co-precipitation synthesis in aqueous medium was applied in the preparation of perovskite-type lanthanum manganese oxide-based powders, i.e. La_0.70Sr_0.30MnO_3?δ (LSM) and La_0.75Sr_0.25Cr_0.5Mn_0.5O_3?δ (LSCrM). The precursors so obtained yielded nano-structured perovskite oxides when treated at 900°C and 800°C, respectively. The measured BET surface areas were in the low-end range for high temperature oxides (4 m² g^?1 and 10 m² g^?1) but the X-ray crystallite size was as low as 50 nm for LSCrM and 90 nm for LSM.     

Homogeneity Region Boundaries of Praseodymium Manganite Pr2 − x MnxO3 ± δ in Air

The solubility boundaries of simple praseodymium and manganese oxides and the PrMn₂O₅ double oxide in PrMnO₃ were determined using X-ray powder patterns of homogeneous phases and heterogeneous compositions of the general formula Pr_{2 ? x} Mn_xO_{3 ± δ} (0.90 <- x <- 1.20; Δx = 0.02) obtained by ceramic synthesis from oxides in air over the temperature range 900–1400°C. The results are presented in the form of a fragment of the phase diagram of the Pr-Mn-O system in air. The suggestion was made that the solubility of praseodymium oxide in PrMnO₃ was caused by crystal structure defects, and that of manganese oxides, by structure defects and the partial replacement of praseodymium cations by manganese ions in the cuboctahedral sites of the perovskite-like crystal lattice. The suggestions made can be verified by a systematic study of the oxygen nonstoichiometry of Pr_{2 ? x} Mn_xO_{3 ± δ} manganite depending on x and the temperature of synthesis.     

利用多酸在SBA-15孔道中制备组分可调的氧化钼-五氧化二钒纳米线

A new approach was developed to fabricate nanowires of mixed oxides MoO3-V2O5 inside the channels of mesoporous silica SBA-15. The method involves functionalization of the channel surface of SBA-15 with aminosilane groups, immobilization of Keggin-type molybdovanadophosphoric acids through an acid-base interaction, and heat treatment. The immobilization of the heteropolyacid containing mixed addenda makes the molar ratio of the loaded components controllable. The formation of the MoO3-V2O5 nanowires inside the channels was monitored by variable temperature in situ XRD. The materials obtained by heat treatment at 400℃ for 5 h were characterized by TEM, N2-sorption measurements, laser Raman spectra and UV-Vis diffuse reflectance spectra. Further heat treatment of the MoO3-V2O5 nanowires inside the SBA-15 channels at higher temperature (700℃) destroys the framework integrity of SBA-15 by complete sublimation of MoO3 through the SBA-15 channel walls.     

MnO x -Al2O3 catalysts for deep oxidation prepared with the use of mechanochemical activation: The effect of synthesis conditions on the phase composition and catalytic properties

The catalytic activity of alumina-manganese catalysts in the oxidation of CO was studied. The MnO _x -Al₂O₃ catalysts were prepared by an extrusion method with the introduction of mechanically activated components (manganese oxide and its mixtures with aluminum oxide, aluminum hydroxide, and a mixture of a manganese salt with aluminum hydroxide) into a paste of aluminum hydroxide followed by thermal treatment in air or argon at 1000°C. In the majority of cases, the catalysts contained a mixture of the phases of β-Mn₃O₄ (Mn₂O₃), α-Al₂O₃, and δ-Al₂O₃. The presence of low-temperature δ-Al₂O₃ suggested the incomplete interaction of manganese and aluminum oxides. It was found that the catalytic activity of MnO _x -Al₂O₃ depends on the degree of interaction of the initial reactants, and its value is correlated with the amount of β-Mn₃O₄ in the active constituent. The intermediate thermal treatment of components at 700°C negatively affects the catalytic activity as a result of the formation of Mn₂O₃ and the coarsening of particles, which levels the results of mechanochemical activation. The greatest degree of interaction between Al- and Mn-containing components was reached in the selection of mechanochemical activation conditions by decreasing the size of grinding bodies, optimizing the time of mechanochemical activation, and using the mechanochemical activation of precursor mixtures. As a result of mechanochemical activation, the initial reactants were dispersed, the amounts of MnO₂ and Mn₂O₃ changed, and defects were formed; this strengthened the interaction of components and increased catalytic activity.     

Thermal decomposition of managanese oxyhydroxide

Temperature-programmed thermal decomposition of γ- and α-manganese oxyhydroxide has been studied between 20 and 670°C under vacuum and under a low pressure (10 Torr) of oxygen. Solid products at various temperatures have been analyzed by X-ray diffractometry. Under vacuum γ-MnOOH decomposed below 400°C to a mixture of Mn₅O₈, α-Mn₃O₄, and water according to the reaction scheme: 8MnOOH → Mn₅O₈ + Mn₃O₄ + 4H₂O. Above this temperature Mn₅O₈ was converted to α-Mn₃O₄ as a result of oxygen removal. The vacuum dehydration at 250°C of oxyhydroxide rich in α-MnOOH led to the formation of a new modification of Mn₂O₃ isostructural with corundum (α-Al₂O₃). In oxygen both oxyhydroxides decomposed to β-MnO₂. γ-MnOOH transformed directly to β-MnO₂ while α-MnOOH appeared to transform via corundum-phase Mn₂O₃ as an intermediate.     

Synthesis and thermal stability of hydrotalcites containing manganese

The hydrotalcite based upon manganese known as charmarite Mn₄Al₂(OH)₁₂CO₃·3H₂O has been synthesised with different Mn/Al ratios from 4:1 to 2:1. Impurities of manganese oxide, rhodochrosite and bayerite at low concentrations were also produced during the synthesis. The thermal stability of charmarite was investigated using thermogravimetry. The manganese hydrotalcite decomposed in stages with mass loss steps at 211, 305 and 793 °C. The product of the thermal decomposition was amorphous material mixed with manganese oxide. A comparison is made with the thermal decomposition of the Mg/Al hydrotalcite. It is concluded that the synthetic charmarite is slightly less stable than hydrotalcite.