Reduction behavior of iron oxides in hydrogen and carbon monoxide atmospheres

Jóźwiak, W. K.; Kaczmarek, E.; Maniecki, Tomasz P.; Ignaczak, W.; Maniukiewicz, Waldemar

doi:10.1016/j.apcata.2007.03.021

Cited by 609 publications

(387 citation statements)

References 30 publications

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“…S2), but CO and H 2 reduce iron oxides at higher temperatures producing CO 2 and water respectively [9] . In the case of CO, the Pt cluster efficiently adsorbs the molecule and delivers it to the cluster/support interface where it extracts O lattice to create CO 2 .…”

mentioning

confidence: 98%

An Atomic‐Scale View of CO and H₂ Oxidation on a Pt/Fe₃O₄ Model Catalyst

et al. 2015

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Metal-support interactions are frequently invoked to explain the enhanced catalytic activity of metal nanoparticles dispersed over reducible metal-oxide supports, yet the atomic scale mechanisms are rarely known. Here, we use scanning tunneling microscopy to study a Pt 1-6 /Fe 3 O 4 model catalyst exposed to CO, H 2 , O 2 , and mixtures thereof, at 550 K. CO extracts lattice oxygen at the cluster perimeter to form CO 2 , creating large holes in the metal-oxide surface. H 2 and O 2 dissociate on the metal clusters and spill over onto the support. The former creates create surface hydroxyl groups, which react with the support to desorb water, while atomic oxygen reacts with Fe from the bulk to create new Fe 3 O 4 (001) islands. The presence of the Pt is crucial because it catalyses reactions that already occur on the bare iron-oxide surface, but at higher temperatures. Variations in the CO oxidation activity of nominally similar metal nanoparticles dispersed over different metal oxides [1] are a clear indicator of metal-support interactions, but the mechanisms by which the metal oxide gets involved are difficult to ascertain. The support is known to transfer electrons to (or from) the clusters [2] , modifying their shape and adsorption properties, and adsorb reactants and promoters (e.g. water) that can speed up the reaction [3] . At elevated temperature, the so-called Mars-van Krevelen (MvK) mechanism [1i] can occur, where CO molecules extract lattice oxygen (O lattice ) at the cluster perimeter forming CO 2 , and gas phase O 2 repairs the surface to complete the catalytic cycle. While there is mounting evidence that MvK plays a role when reducible metal oxides are utilized as the support [1i] , there is little atomic-scale information available to better understand how the process occurs.In this paper, we use scanning tunneling microscopy (STM) to follow the evolution of a Pt/Fe 3 O 4 (001) model catalyst exposed to CO, O 2 and H 2 at 550 K. Holes and islands in the vicinity of Pt clusters provide direct evidence of reduction and oxidation of the metal oxide in CO and O 2 rich atmospheres respectively, while dissociation and spillover of H 2 leads to hydroxylation of the support lattice. We interpret our results as the metal catalyzing reactions that otherwise occur between the reactants and support at higher temperatures.An STM image of the Pt/Fe 3 O 4 (001) model catalyst utilized as the basis for this work is shown in Figure 1. The Fe 3 O 4 (001)-support [4] exhibits large, flat terraces ( Fig. 1, inset) characterized by rows of protrusions related to surface Fe atoms in STM images. The rows rotate by 90° from terrace to terrace, a consequence of the spinel structure. Surface O atoms are not imaged because they have no density of states in the vicinity of the Fermi energy [5] . Surface OH groups, formed through the reaction of water and oxygen vacancies during sample preparation [6] , modify the density of states of the neighboring Fe atoms making them appear brighter in STM images [7] . The sur...

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confidence: 98%

An Atomic‐Scale View of CO and H₂ Oxidation on a Pt/Fe₃O₄ Model Catalyst

et al. 2015

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“…100 8C than that over Fe 0.5 Mn 0.5-TiO x , which was mainly due to the absence of iron species. During the reduction process of iron and manganese containing catalysts, a small fraction of iron species was firstly reduced to metallic Fe 0 nanoparticles, which could dissociate H 2 into H atoms; in the presence of the in situ formed water vapor, the dissociated H atoms could be transferred effectively to further reduce the manganese oxides through the so-called H-spillover effect [62][63][64]. This Hspillover effect could significantly lower the reduction temperature of T 2 peak, which was a new feature introduced by the coexistence of iron and manganese species.…”

Section: H 2 -Tprmentioning

confidence: 99%

Effect of manganese substitution on the structure and activity of iron titanate catalyst for the selective catalytic reduction of NO with NH3

Liu

Ding

et al. 2009

Applied Catalysis B: Environmental

603

355

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“…The study did not distinguish between co-current and countercurrent flow of hydrogen, and no data are presented on the concentration of hydrogen in the steam generator tubes. Given the results of Kizu and Tanabe [84,85], however, it is likely that counter flow of hydrogen was the cause of the reduction in tritium permeation rate across the steam generator tubes rather than just the mere presence of hydrogen with tritium.…”

Section: Countercurrent Hydrogen Flowmentioning

confidence: 99%

“…Other oxide catalysts might be used for higher temperatures. MnO 2 is able to reduce hydrogen effectively in the temperature range 300-500ºC [83], and Fe 2 O 3 works effectively as a reduction catalyst over the range 150-880ºC [84].…”

Section: Chemical Transformationmentioning

confidence: 99%

Tritium Barrier Materials and Separation Systems for the NGNP

Sherman¹,

Adams²

2008

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Reduction behavior of iron oxides in hydrogen and carbon monoxide atmospheres

Cited by 609 publications

References 30 publications

An Atomic‐Scale View of CO and H₂ Oxidation on a Pt/Fe₃O₄ Model Catalyst

An Atomic‐Scale View of CO and H₂ Oxidation on a Pt/Fe₃O₄ Model Catalyst

Effect of manganese substitution on the structure and activity of iron titanate catalyst for the selective catalytic reduction of NO with NH3

Tritium Barrier Materials and Separation Systems for the NGNP

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Reduction behavior of iron oxides in hydrogen and carbon monoxide atmospheres

Cited by 609 publications

References 30 publications

An Atomic‐Scale View of CO and H2 Oxidation on a Pt/Fe3O4 Model Catalyst

An Atomic‐Scale View of CO and H2 Oxidation on a Pt/Fe3O4 Model Catalyst

Effect of manganese substitution on the structure and activity of iron titanate catalyst for the selective catalytic reduction of NO with NH3

Tritium Barrier Materials and Separation Systems for the NGNP

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Product

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An Atomic‐Scale View of CO and H₂ Oxidation on a Pt/Fe₃O₄ Model Catalyst

An Atomic‐Scale View of CO and H₂ Oxidation on a Pt/Fe₃O₄ Model Catalyst