A M�ssbauer study of the reduction of hematite in hydrogen at 535� C

Graham, M. J.; Channing, D. A.; Swallow, G. A.; Jones, Richard D.

doi:10.1007/bf00541400

Cited by 13 publications

(5 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…No other phase, besides magnetite, was detected. As wustite is unstable below 575 °C 44 , it is not probable that this phase could be in the solids produced in the present work. By studying the reduction of iron oxides, it has been noted 45 that metallic iron is formed directly from magnetite below that temperature, but through the intermediate wustite phase above 575 °C.…”

Section: Discussionmentioning

confidence: 84%

Chromium and Copper-Doped Magnetite Catalysts for the High Temperature Shift Reaction

Quadro¹,

Dias²,

Amorim³

et al. 1999

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

Foi obtida magnetita pura e dopada com cromo e cobre, visando produzir catalisadores, na fase ativa, destinados à conversão de monóxido a dióxido de carbono a altas temperaturas (reação de HTS). As amostras foram preparadas por aquecimento do hidroxoacetato de misto ferro (III), IHA, na faixa de 150-400 °C, e caracterizados por análise química, difração de raios-X, análise térmica (DSC e TG), espectroscopia no infravermelho, medidas de área específica, microscopia eletrônica de varredura e microssonda eletrônica de raios X. Observou-se que a presença do cobre favorece a formação da magnetita mas não afeta a cristalinidade dos sólidos, de modo significativo. Ambos os dopantes melhoram o desempenho dos catalisadores: o cromo atua como estabilizador, enquanto o cobre aumenta a atividade intrínseca. Entretanto, este último favorece a sinterização, levando à formação de sólidos com baixas áreas superficiais. O efeito sinérgico desses dopantes é aumentar a atividade catalítica e a área superficial dos sólidos.Copper and chromium-doped magnetite was prepared to be used as catalysts, in the active phase, in the high temperature shift (HTS) reaction. Samples were produced by heating a mixed hydrate ferric oxyhydroxide (IHA) in the range of 150-400 °C and characterized by means of chemical analysis, X-ray diffraction, thermal analysis (DSC and TG), infrared spectroscopy, surface area measurements, scanning electron microscopy and X-ray microanalysis. It was found that copper favors magnetite formation but does not affect significantly the crystallinity of the solids. Both chromium and copper improve the performance of the catalysts towards the HTS reaction: chromium acts as a stabilizer whereas copper increases the intrinsic activity. However, copper favors sinterization leading to solids with low surface areas. The increase in the catalytic activity and in the surface area of the solids reflects the synergy of these dopants.

show abstract

Section: Discussionmentioning

confidence: 84%

Chromium and Copper-Doped Magnetite Catalysts for the High Temperature Shift Reaction

Quadro¹,

Dias²,

Amorim³

et al. 1999

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…Signi cantly different results were later reported by Graham and his partners 4) in a similar experiment. Rau et al 5) also reported that they did not nd any metastable wüstite in their experiment.…”

Section: Introductionmentioning

confidence: 55%

Mechanism of Metastable Wüstite Formation in the Reduction Process of Iron Oxide below 570℃

2016

View full text Add to dashboard Cite

The possibility of metastable wüstite below 570 C during the reduction of iron oxides was discussed. There was uncertainty regarding the formation of metastable wüstite in the reduction of hematite below 570 C. Planar disregistry (1/δ) was employed to predict the probability of metastable wüstite formation during the reduction process. The calculated results showed that the δ of wüstite/magnetite is similar to that of iron/magnetite with plain and normal structures, but less than ake and nger structures. The difference in disregistry of different geometries of interfaces was suggested to be the principal driving force for the formation of metastable wüstite. This implies that the formation of metastable wüstite always accompanies the nucleation of iron structures with high δ relative to magnetite. The latter structures form easily in supported iron, leading to the relatively common observation of metastable wüstite in an iron catalyst. The analysis showed that the temperature range for metastable wüstite formation, 400 C 500 C, was most likely to occur where it created a predominance of ake and nger structures.

show abstract

“…Significantly, the specific mechanism usually depends on the initial materials. This is why Graham and his partners [ 34 ] “repeated” Romanov's experiment and achieved completely different results. They declared no wustite existed by the Mössbauer study of the reduction of hematite in hydrogen at 535 °C.…”

Section: Resultsmentioning

confidence: 99%

The Ideal and Regular Mechanisms of Hematite Reduction Reactions

Zhang

Xue

Zou

et al. 2022

Crystal Research and Technology

View full text Add to dashboard Cite

The thermodynamic data of iron oxides reduction reactions from the most recognized thermodynamic database (NIST‐JANAF) show remarkable difference between stoichiometric and nonstoichiometric iron oxides. Iron oxides reduction equilibria in both CO‐CO2 and H2‐H2O atmospheres are calculated with Dieckmann's and Weiss’ defect models. Relevant literatures are investigated and reduction experiments are carried out to complement and interpret the newly calculated equilibrium diagram. The results suggest a conjecture of two routes for hematite reduction reactions. With the ideal and widely accepted mechanism, hematite is reduced to magnetite and then to iron below 576 °C, while the reduction route follows the sequence of Fe2O3 → Fe3−δO4 → FexO → Fe above 576 °C. With the regular but always unrecognized mechanism, the reduction process of hematite experiences Fe3O4, FeO, and Fe step by step in all possible temperature above 156 °C. In the regular mechanism, sufficient scattered impurities occupy crystal interstices of magnetite and prevent the newly produced FeO unit cell from dissolving into the solid solution of magnetite, and then the FeO will accumulate above 156 °C. Actually the regular mechanism is hard to realize and usually confused with the ideal mechanism. The presence of the regular mechanism is proved by experimental phenomena of the drop of eutectoid temperature.

show abstract

A M�ssbauer study of the reduction of hematite in hydrogen at 535� C

Cited by 13 publications

References 10 publications

Chromium and Copper-Doped Magnetite Catalysts for the High Temperature Shift Reaction

Chromium and Copper-Doped Magnetite Catalysts for the High Temperature Shift Reaction

Mechanism of Metastable Wüstite Formation in the Reduction Process of Iron Oxide below 570℃

The Ideal and Regular Mechanisms of Hematite Reduction Reactions

Contact Info

Product

Resources

About