Steam-iron process: Influence of steam on the kinetics of iron oxide reduction
TL;DR: In this paper, the effect of water vapour on the kinetics of the steam-iron process was investigated and two models, the competitive model and the inhibitive model, were proposed to predict the behavior of the solid subjected to successive reductive and oxidative cycles.
About: This article is published in International Journal of Hydrogen Energy.The article was published on 2011-10-01. It has received 35 citations till now. The article focuses on the topics: Iron oxide & Reaction rate.
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200 citations
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TL;DR: In this paper, the anaerobic oxidation of ethanol over spinel mixed oxides was studied by means of in situ diffuse reflectance spectroscopy (DRIFTS) and mass spectrometry (MS).
Abstract: The anaerobic oxidation of ethanol over spinel mixed oxides A2+Fe23+O42– (with A = Co2+, Ni2+, or Fe2+) was studied by means of in situ diffuse reflectance spectroscopy (DRIFTS) and mass spectrometry (MS). The nature of the surface species formed during the reaction and its related gas products were discussed. Different reaction pathways were proposed depending on the catalyst composition. Acetates appeared to be important surface intermediates in the case of the Ni ferrite which is at the same time the most basic and easily reducible catalyst from the set studied, whereas with Co and Fe ferrites, more direct pathways to oxidation products were evidenced but at higher temperatures.
62 citations
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TL;DR: In this paper, the effects of the temperature, syngas constituents and reduction degree on the sticking properties of iron ore pellets in the presence of H2-CO mixtures were evaluated.
52 citations
Cites background from "Steam-iron process: Influence of st..."
...H2 has been proved with many advantages of better reducing capabilities, significant potential to reduce energy usage and to decrease corresponding greenhouse gases compared to CO in iron ore reduction [19–23]....
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TL;DR: The results indicate that iron species are embedded into the carbon matrix by lignin melting, suggesting that the representative MBAC product has a comparable phosphate adsorption capacity to most of the reported MBCs and MBACs.
45 citations
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TL;DR: In this article, the impact of gas phase pretreatment of a supported iron-oxide catalyst utilized in aligned carbon nanotube (CNT) growth is studied to understand the correlation between the catalyst oxidation state and the growth characteristics of the aligned CNT forests.
Abstract: The impact of gas-phase pretreatment of supported iron-oxide catalyst utilized in aligned carbon nanotube (CNT) growth is studied to understand the correlation between the catalyst oxidation state and the growth characteristics of the aligned CNT forests. By varying the pretreatment conditions from a reducing to an oxidizing environment, notable changes are observed in both the collective CNT array growth behavior and the individual CNT characteristics. Although the greatest catalytic activity was observed following a full reduction to the zerovalent (metallic) Fe catalyst, growth is also observed from a catalyst composed of both Fe2O3 and Fe3O4 particles. XPS core-level analysis, following pretreatment of the catalyst, emphasizes the critical nature of the combined catalyst–underlayer interaction to achieve optimal catalyst activity during growth and hence the most efficient catalyst reduction process. Additionally, CNT diameters during growth were strongly affected by the pretreatment process. Overall, ...
39 citations
References
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TL;DR: In this article, a relation between the actual transformed volume V and a related extended volume V1 ex is derived upon statistical considerations, and a rough approximation to this relation is shown to lead, under the proper conditions, to the empirical formula of Austin and Rickett.
Abstract: Following upon the general theory in Part I, a considerable simplification is here introduced in the treatment of the case where the grain centers of the new phase are randomly distributed. Also, the kinetics of the main types of crystalline growth, such as result in polyhedral, plate‐like and lineal grains, are studied. A relation between the actual transformed volume V and a related extended volume V1 ex is derived upon statistical considerations. A rough approximation to this relation is shown to lead, under the proper conditions, to the empirical formula of Austin and Rickett. The exact relation is used to reduce the entire problem to the determination of V1 ex, in terms of which all other quantities are expressed. The approximate treatment of the beginning of transformation in the isokinetic range is shown to lead to the empirical formula of Krainer and to account quantitatively for certain relations observed in recrystallization phenomena. It is shown that the predicted shapes for isothermal transfo...
7,448 citations
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TL;DR: In this paper, a three-stage mechanism for the reduction of various iron oxides in hydrogen and carbon monoxide atmospheres has been investigated by temperature programmed reduction (TPR H2 and TPR CO ), thermo-gravimetric and differential temperature analysis (TG-DTA-MS), and conventional and in situ XRD methods.
Abstract: The reduction of various iron oxides in hydrogen and carbon monoxide atmospheres has been investigated by temperature programmed reduction (TPR H2 and TPR CO ), thermo-gravimetric and differential temperature analysis (TG-DTA-MS), and conventional and “ in situ ” XRD methods Five different compounds of iron oxides were characterized: hematite α-Fe 2 O 3 , goethite α-FeOOH, ferrihydrite Fe 5 HO 8 ·4H 2 O, magnetite Fe 3 O 4 and wustite FeO In the case of iron oxide-hydroxides, goethite and ferrihydrite, the reduction process takes place after accompanying dehydration below 300 °C Instead of the commonly accepted two-stage reduction of hematite, 3 α-Fe 2 O 3 → 2 Fe 3 O 4 → 6 Fe, three-stage mechanism 3Fe 2 O 3 → 2Fe 3 O 4 → 6FeO → 6Fe is postulated especially when temperature of reduction overlaps 570 °C Up to this temperature the postulated mechanism may also involve disproportionation reaction, 3Fe 2+ ⇌ 2Fe 3+ + Fe, occurring at both the atomic scale on two-dimensional interface border Fe 3 O 4 /Fe or stoichiometrically equivalent and thermally induced, above 250 °C, phase transformation—wustite disproportionation to magnetite and metallic iron, 4FeO ⇌ Fe 3 O 4 + Fe Above 570 °C, the appearance of wustite phase, as an intermediate of hematite reduction in hydrogen, was experimentally confirmed by “ in situ ” XRD method In the case of FeO–H 2 system, instead of one-step simple reduction FeO → Fe, a much more complex two-step pathway FeO → Fe 3 O 4 → Fe up to 570 °C or even the entire sequence of three-step process FeO → Fe 3 O 4 → FeO → Fe up to 880 °C should be reconsidered as a result of the accompanying FeO disproportionation wustite ⇌ magnetite + iron manifesting its role above 150 °C and occurring independently on the kind of atmosphere—inert argon or reductive hydrogen or carbon monoxide The disproportionation reaction of FeO does not consume hydrogen and occurs above 200 °C much easier than FeO reduction in hydrogen above 350 °C The main reason seems to result from different mechanistic pathways of disproportionation and reduction reactions The disproportionation reaction wustite ⇌ magnetite + iron makes simple wustite reduction FeO → Fe a much more complicated process In the case of thermodynamically forced FeO disproportionation, the oxygen sub-lattice, a closely packed cubic network, does not change during wustite → magnetite transformation, but the formation of metallic iron phase requires temperature activated diffusion of iron atoms into the region of inter-phase FeO/Fe 3 O 4 Depending on TPR H2 conditions (heating rate, velocity and hydrogen concentration), the complete reduction of hematite into metallic iron phase can be accomplished at a relatively low temperature, below 380 °C Although the reduction behavior is analogical for all examined iron oxides, it is strongly influenced by their size, crystallinity and the conditions of reduction
532 citations
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TL;DR: In this article, the reduction of Fe3O4 by H2 in the temperature range of 210-950 °C was investigated and the results showed that the reaction rate is controlled by diffusion and SEM observations confirm the sintering of the reaction products.
394 citations
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TL;DR: In this paper, temperature-programmed reduction was used to characterize precipitated iron oxide samples and two-stage reduction was observed: Fe2O3 was reduced to Fe3O4 and then reduced to metallic Fe.
272 citations