Thermal decomposition of managanese oxyhydroxide
TL;DR: In this article, temperature-programmed thermal decomposition of α-manganese oxyhydroxide has been studied between 20 and 670°C under vacuum and under a low pressure (10 Torr) of oxygen.
About: This article is published in Journal of Solid State Chemistry.The article was published on 1980-01-01. It has received 41 citations till now. The article focuses on the topics: Thermal decomposition & Oxygen.
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TL;DR: 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, indicating a relation between the SCR process and active surface oxygen.
Abstract: 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. MnO2 appears to exhibit the highest activity per unit surface area, followed by Mn5O8, Mn2O3, Mn3O4 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. Mn2O3 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 15NH3. 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 Mn3O4 under the applied conditions. In the oxidation of ammonia the degree of oxidation of the nitrogen containing products (N2, N2O, NO) increases with increasing temperature and with increasing oxidation state of the manganese. A reaction model is proposed to account for the observed phenomena.
634 citations
TL;DR: In this paper, a structural description of the electrochemically active forms of manganese dioxide, known as γ- and e-MnO 2 and used in Leclanche and alkaline batteries, in relation to an investigation of their electrochemical properties is presented.
581 citations
TL;DR: In this article, the transition metal L 2,3 electron energy-loss spectra for a wide range of V-, Mn- and Fe-based oxides were recorded and carefully analyzed for their correlation with the formal oxidation states of transition metal ions.
445 citations
TL;DR: In this paper, the mechanism of O2 reduction in air electrode using MnOx as electrocatalysts to effect a four-electron reduction of HO2− into O2 and OH− catalyzed by MnOx was investigated.
338 citations
TL;DR: In this paper, a coprecipitation method was used to obtain the reciprocal solubilities calculated from the XRD patterns approach the thermodynamic ones for both propane and propene oxidation.
Abstract: Mn2O3–Fe2O3 powders have been prepared by a coprecipitation method. The pure compounds have been characterized as constituted of α-Fe2O3 (haematite) and α-Mn2O3 (bixbyite) while the mixed oxides are constituted of a mixture of haematite- and bixbyite-structure solid solutions. The observed reciprocal solubilities calculated from the XRD patterns approach the thermodynamic ones. α-Mn2O3 is more active than α-Fe2O3 as catalyst for both propane and propene oxidation. However, α-Mn2O3 is less active than Mn3O4 powder. Propene oxidation is in all cases very selective to CO2 while propane oxidation gives rise to significant amounts of propene on α-Fe2O3. Mn2O3–Fe2O3 powders are slightly more active than α-Mn2O3 as combustion catalysts. The selectivities to propene upon propane oxidation decrease with increasing Mn content.
194 citations
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162 citations
TL;DR: In this paper, a critical summary of the previous interpretations of the potential of the manganese-dioxide electrode is given; this potential is discussed on the basis of a general thermodynamic theory of Vetter.
105 citations
TL;DR: In this paper, die Oxydation von Mangan(II)-hydroxyd and von ammoniakalischen Mangan-II-salzlosungen with Sauerstoff and Wasserstoffperoxyd verfolgt.
Abstract: 1. Es wird die Oxydation von Mangan(II)-hydroxyd und von ammoniakalischen Mangan(II)-salzlosungen mit Sauerstoff und Wasserstoffperoxyd verfolgt. Rontgenographisch und analytisch sind die folgenden Oxydationsprodukte festgestellt worden: oxydiertes Manganhydroxyd, Mangan(II(, (III)-Doppelhydroxyd, Hausmannit, Hydrohausmannit, α, β, γ-MnOOH, Mangan(II)-manganit. Die Bedingungen, unter denen sich diese Verbindungen bilden, werden im einzelnen beschrieben.
91 citations
TL;DR: In this paper, the authors showed that the JAHN-TELLER distortion is the crosspoint of two different functions attributed to the crystal species α-MnOOH and γ-mnO2, respectively.
Abstract: The oxidation of γ-MnOOH (manganite) in oxygen and its disproportionation in HNO3 lead topotactically to β-MnO2. The oxidation of synthetic α-MnOOH (groutite) in oxygen depends on its cristallite size; finely divided crystals oxidise rapidly to Mn5O8 which usually is stable but yields β-MnO2 by further oxidation. Larger crystals of disperse synthetic α-MnOOH are topotactically transformed to γ-MnO2. In HNO3 α-MnOOH disproportionates into γ-MnO2 and Mn2+. Though strictly topotactical, the reaction α-MnOOH → γ-MnO2 is not single-phase as might be expected. The discontinuity in the function: JAHN-TELLER distortion vs. reaction rate, may simply be interpreted as the crosspoint of two different functions attributed to the crystal species α-MnOOH and γ-MnO2, respectively. This distortion confirms the presence of Mn3+ in manganite and nsutite. The wide variety of possible X ray powder patterns of the phase γ-MnO2 is explained by the superposition of, (i) cristallite size broadening, (ii) intergrowth structure effects on the profile, and (iii) BRAGG angle shifts due to substitution of part of Mn4+ by Mn3+.
80 citations