Characterization of the thermal genesis course of manganese oxides from inorganic precursors

Nohman, A.K.H.; Zaki, Mohamed I.; Mansour, S.A.A.; Fahim, R. B.; Kappenstein, Charles

doi:10.1016/0040-6031(92)80281-z

Cited by 53 publications

(17 citation statements)

References 21 publications

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“…These results demonstrate that the preparation variables (Table 1) applied to the hydrothermal processing of the redox reaction between MnSO 4 and MnO 4 -solutions (Guyard 1964) allowed the successful diversification of the bulk composition of the oxide products. The presence of K + ions in the aqueous preparation appeared to be the governing factor for the formation of the cryptomelanelike oxide [Mn(1)], as reported previously for the course of the solid decomposition of permanganate compounds (Nohman et al 1992). In contrast, the presence of the much smaller Na + ions led to the formation of the nsutite-like oxide [Mn(2)] which contained narrower structural tunnels (1 × 2) than cryptomelane (2 × 2).…”

Section: Surface Characterization Techniquesmentioning

confidence: 76%

“…2.4% during step-II (T max = 850ºC) corresponding to the decomposition of Mn 5 O 8 into Mn 2 O 3 . The third, and last, step (T max = 980ºC) was due to the decomposition of Mn 2 O 3 into Mn 3 O 4 (Nohman et al 1992). Thus, the thermal decomposition of Mn(2) and Mn(3) did not involve MnO 2 ® Mn 5 O 8 conversion (step-II).…”

Section: Chemical and Phase Compositionmentioning

confidence: 99%

“…A different TG curve was obtained for Mn(1) which displayed three ML steps, following a dehydration step (3.8%) with a maximum at 220ºC. The ML step-I (T max = 550ºC) corresponded to the conversion of MnO 2 into Mn 5 O 8 (Nohman et al 1992). The product of step-I suffered a mass loss of ca.…”

Section: Chemical and Phase Compositionmentioning

confidence: 99%

“…To maintain electrical neutrality throughout the solid lattice, the bulk structure must accommodate cationic species of foreign elements (mostly alkali and alkaline earth metals) inside the tunnels (O'Young 1991). A nearly stoichiometric composition ) is only found in pyrolusite (Nohman et al 1992) which, as a result, contains the narrowest tunnels (1 × 1) amongst this class of manganese(IV) oxides.…”

Section: Introductionmentioning

confidence: 99%

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Surface Texture of Microcrystalline Tunnel-Structured Manganese(IV) Oxides: Nitrogen Sorptiometry and Electron Microscopy Studies

Ali

Al‐Sagheer

Zaki

2002

Adsorption Science & Technology

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Three different modifications of manganese(IV) oxide, viz. cryptomelane, nsutite and todorokite-like, were synthesized by hydrothermal methods. The bulk chemical composition, phase composition, crystalline structure and particle morphology of the resulting materials were determined by thermogravimetry, atomic absorption spectroscopy, X-ray diffractometry, infrared spectroscopy and scanning electron microscopy. The surface chemical composition, texture and structure were assessed using X-ray photoelectron microscopy, nitrogen sorptiometry and high-resolution electron microscopy. The results highlighted the hydrothermal conditions under which such tunnel-structured modifications of manganese(IV) oxide can be successfully synthesized. Moreover, they revealed that (i) the bulk was microcrystalline, (ii) the crystallites were either fibrils (cryptomelane and nsutite) or rod-like (todorokite) with low-index exposed facets, (iii) the surface chemical composition mostly reflected that of the bulk and (iv) the surface texture was linked with high specific areas, slit-shaped mesopores associated with particle interstices and micropores which allowed surface accessibility to the bulk tunnels of the test oxides. The application of such test oxides as shape-selective oxidation catalysts appears worthy of investigation.

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Section: Surface Characterization Techniquesmentioning

confidence: 76%

Section: Chemical and Phase Compositionmentioning

confidence: 99%

Section: Chemical and Phase Compositionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Surface Texture of Microcrystalline Tunnel-Structured Manganese(IV) Oxides: Nitrogen Sorptiometry and Electron Microscopy Studies

Ali

Al‐Sagheer

Zaki

2002

Adsorption Science & Technology

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“…Manganese oxides are, as a rule, deposited onto metals by pyrolytic and electrochemical methods [7,8].…”

mentioning

confidence: 99%

Composition and Catalytic Activity of Plasma-Electrolytic Manganese Oxide Films on Titanium, Modified with Silver Compounds

et al. 2005

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The effect of impregnation in aqueous solutions of AgNO 3 and subsequent calcination of manganese oxide surface structures produced on a titanium substrate by plasma-electrolytic oxidation on their catalytic activity in oxidation of CO was studied.The most efficient catalysts for catalytic oxidation of CO are precious metals [1]. However, these metals are expensive and their pretreatment is complicated. Therefore, a considerable attention is given to formation processes and properties of catalysts based on compounds of nonprecious metals and, in particular, oxides [2]. Recently, composite structures containing a metal with a deposited oxide layer and a catalytically active additive have been finding increasing use [3,4]. An important advantage of the composites of this kind is the high thermal and electrical conductivity of the substrate.Manganese oxides are among the most active oxidation catalysts [5,6]. Manganese oxides are, as a rule, deposited onto metals by pyrolytic and electrochemical methods [7,8].Oxide systems of various compositions with a developed surface can be formed on metals by plasmaelectrolytic treatment (PET) [9]. A specific feature of this technique is that high-temperature reactions occur on local areas of the surface under the action of electric discharges. These reactions include thermolytic transformations of solution components at the anode and incorporation of the forming insoluble compounds into the surface structures. In many cases, the film thus formed is a [sandwich] constituted both by oxides of a metal being treated and by compounds based on electrolyte components.Recently, conditions (electrolytes, modes) have been suggested under which layers containing compounds of bi-, tri-, and polyvalent metals can be formed by plasma-electrolytic oxidation on rectifying metals [10 312]. In particular, manganese oxide layers with a layered structure (Ti/TiO 2 /Mn 2 O 3 3Mn 3 O 4 ) have been obtained on titanium in aqueous electrolytes containing Na 2 B 4 O 7 and Mn(CH 3 COO) 2 [10 3 12]. The content of manganese in the surface layer (2 to 60 wt %) and the morphology of the resulting oxide structures depend both on the concentration of manganese acetate in the electrolyte and on the formation conditions. These PET films on titanium catalyze CO oxidation at temperatures in the range 200 3350oC [13]. The catalytic activity of structures of this kind compares well with that of manganese oxide layers obtained on the surface of titanium by the conventional pyrolytic method. The rate of CO conversion by the anodic structures formed depends on their content of manganese.It is known [14 317] that addition of silver to certain metal oxides markedly improves their catalytic properties. In addition, silver is relatively accessible, compared with other precious metals. In this study we examined the influence exerted by silver additives on the composition and catalytic properties of manganese oxide films formed on titanium by plasma-electrolytic oxidation. EXPERIMENTALOxide layers were formed on 0.5 0 2....

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ChemInform Abstract: Characterization of the Thermal Genesis Course of Manganese Oxides from Inorganic Precursors.

et al. 1993

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Characterization of the Thermal Genesis Course of Manganese Oxides from Inorganic Precursors.-The thermal events occurring during decomposition of the precursors: Mn(NO3)2·6 H2O, NH4MnO4, and MnOx(OH)y are monitored by TG and DTA. The chemical and phase composition of the products MnOx (β-MnO2, α-Mn2O3, Mn3O4, Mn5O8), characterized by XRD and IR spectroscopy, are critically controlled by the nature of the precursor compound and the calcination temp. applied. -(NOHMAN, A. K. H.; ZAKI, M. I.; MANSOUR, S. A. A.; FAHIM, R. B.; KAPPENSTEIN, C.; Thermochim.

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Characterization of the thermal genesis course of manganese oxides from inorganic precursors

Cited by 53 publications

References 21 publications

Surface Texture of Microcrystalline Tunnel-Structured Manganese(IV) Oxides: Nitrogen Sorptiometry and Electron Microscopy Studies

Surface Texture of Microcrystalline Tunnel-Structured Manganese(IV) Oxides: Nitrogen Sorptiometry and Electron Microscopy Studies

Composition and Catalytic Activity of Plasma-Electrolytic Manganese Oxide Films on Titanium, Modified with Silver Compounds

ChemInform Abstract: Characterization of the Thermal Genesis Course of Manganese Oxides from Inorganic Precursors.

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