Microstructures and Spectroscopic Properties of Cryptomelane-type Manganese Dioxide Nanofibers

Gao, Tao; Glerup, M.; Krumeich, Frank; Nesper, Reinhard; Fjellvåg, Helmer; Norby, Poul

doi:10.1021/jp804924f

Cited by 417 publications

(377 citation statements)

References 50 publications

(132 reference statements)

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“…purge Ar 20 ml/ min) at a temperature ramp of 10°C/min in the range from room temperature to 800°C. [36,37]. The Raman spectra of bulk-doped manganese catalysts depict characteristic peaks of the nanostructured phases [38], confirming the XRD results.…”

Section: Reactivity Testssupporting

confidence: 80%

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

et al. 2016

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The effect of surface and bulk potassium promotion on the transition metal oxides (Mn, Fe, Co) catalytic activity in catalytic soot oxidation was investigated. The surface promotion was obtained via incipient wetness impregnation, whereas the bulk promotion-nanostructuration-was obtained via wet chemical synthesis or solid state reaction leading to mixed oxide materials. The introduction of potassium into the transition metal oxide matrix results in the formation of tunneled or layered structures, which enable high potassium mobility. The structure of the obtained materials was verified by powder X-ray diffraction and Raman spectroscopy and the catalytic activity in soot oxidation was determined by TPO-QMS and TGA. It was found that the surface promotion does not alter the metal oxide structure and leads to either enhancement (Mn, Fe) or deterioration (Co) of the catalytic activity. Simultaneously, the catalytic activity in soot combustion of the potassium structured oxides is strongly enhanced. The most active, cobalt oxide based catalyst significantly lowers the temperature of 50 % of soot conversion by *350°C comparing to the non-catalyzed process. The study allows for the establishment of rational guidelines for designing robust materials for DPF applications based on ternary metal oxides.

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Section: Reactivity Testssupporting

confidence: 80%

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

et al. 2016

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“…Experimentally, the band gap for cryptomelane, i.e. α-MnO2 with K + , is 1.32 eV [39], agreeing well with our calculations.…”

Section: Resultssupporting

confidence: 89%

Carbon dioxide sorption in a nanoporous octahedral molecular sieve

Williamson¹,

Nelson²,

Li³

2015

J. Phys. D: Appl. Phys.

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We have performed first-principles density functional theory calculations, incorporated with van der Waals interactions, to study CO2 adsorption and diffusion in nanoporous solid -OMS-2 (Octahedral Molecular Sieve). We found the charge, type, and mobility of a cation, accommodated in a porous OMS-2 material for structural stability, can affect not only the OMS-2 structural features but also CO2 sorption performance. This paper targets K + , Na + , and Ba 2+ cations. First-principles energetics and electronic structure calculations indicate that Ba 2+ has the strongest interaction with the OMS-2 porous surface due to valence electrons donation to the OMS-2 and molecular orbital hybridization. However, the Ba-doped OMS-2 has the worst CO2 uptake capacity. We also found evidence of sorption hysteresis in the K-and Nadoped OMS-2 materials.

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“…With the increase in the temperature to 750°C, the weight loss increases to 6.6, 5.4 and 4.66 % (for K-OMS-2RS, K-OMS-2RC and K-OMS-2RA, respectively), which is due to the release of the water molecules inside the tunnels, besides the desorption of the structural oxygen close to the surface (related with the formation of lattice vacancies without decomposition of the material). A weight loss of *1.0, 3.0 and 2.3 % at 750-950°C, and 2.6, 3.1 and 2.5 % at up to 950°C occurred on using K-OMS-2RS, K-OMS-2RC and K-OMS-2RA, respectively, which implies the transformation of cryptomelane to bixbyite (Mn 2 O 3 ) and then to hausmannite (Mn 3 O 4 ) species [23,24], with total weight loss 15.20, 16.40 and 13.06 %. The total weight loss for acetate material (Fig.…”

Section: Differential and Gravimetric Thermal Analysis (Dta And Tga)mentioning

confidence: 98%

Preparation of nano-structured cryptomelane materials for catalytic oxidation reactions

et al. 2016

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Manganese-based octahedral molecular sieves of the type K-OMS-2 (cryptomelane structure) were prepared via reflux method by synproportionation of KMnO 4 and Mn 2? in acidic aqueous suspension. For this method, different manganese anions (sulphate, chloride and acetate) were used, which exert a strong influence on the prepared materials. Several techniques such as X-ray diffraction, Fourier transformer infrared, Raman spectroscopy, transmission electron microscopy, differential and gravimetric thermal analysis and H 2 -temperature programmed reduction were used to characterize the prepared samples. The results revealed that the prepared samples were mainly pure mono-phase cryptomelane materials. The obtained K-OMS-2 material on using the sulphate anion has more available lattice oxygen as compared to that prepared by the other anions. The catalytic activity of the prepared samples was tested towards the oxidative dehydrogenation of cyclohexane. Over the K-OMS-2RS sample, cyclohexane conversion was significantly higher than the other prepared samples.

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Microstructures and Spectroscopic Properties of Cryptomelane-type Manganese Dioxide Nanofibers

Cited by 417 publications

References 50 publications

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

Carbon dioxide sorption in a nanoporous octahedral molecular sieve

Preparation of nano-structured cryptomelane materials for catalytic oxidation reactions

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