Atomic-Scale View of Redox-Induced Reversible Changes to a Metal-Oxide Catalytic Surface:  VOx/α-Fe2O3(0001)

Kim, Hyun-Tak; Escuadro, A. A.; Stair, Peter C.; Bedzyk, Michael J.

doi:10.1021/jp067862s

Cited by 19 publications

(35 citation statements)

References 25 publications

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“…7, where we can see that the 1 ML oxidized V distribution is similar to the 0.5 ML reported case [2], except that the B/A relative site occupation fraction ratio is higher for 1 ML. Interpreting these results further: the A-site (closer to underlying oxygen layer) appears stable with respect to the coverage change, existing in both 0.5 ML and 1 ML as-deposited surfaces.…”

Section: Comparison Of Experiments With Theorysupporting

confidence: 76%

“…Experimental studies of submonolayer V adsorption on clean hematite (0 0 0 1) with subsequent repeatable oxidization/reduction cycles were reported by Kim et al [2], using atom-resolved X-ray standing wave measurements (XSW) to detect V site geometry and X-ray photoemission spectroscopy (XPS) to detect electronic structure changes. In I the general experimental and theoretical background was presented, and theoretical methodology was described.…”

Section: Introductionmentioning

confidence: 99%

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Adsorption of V on a hematite (0 0 0 1) surface and its oxidation: Monolayer coverage

Jin

Kim

et al. 2007

Surface Science

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The adsorption of a monolayer of V on idealized Fe-and oxygen-terminated hematite (0 0 0 1) surfaces and subsequent oxidation under atomic O adsorption are studied by density functional theory. Theoretical results are compared with X-ray surface standing wave and X-ray photoelectron spectroscopic measurements, and interpreted in the light of data on sub-monolayer coverages. Near-surface Fe reduction under V adsorption and accompanying structural relaxation are examined. These effects and subsequent response to oxidation, are found to be highly site specific. A full monolayer of oxygen leads to a V 5+ state and reoxidation of subsurface Fe to the trivalent state, seen in both theory and experiment.

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Section: Comparison Of Experiments With Theorysupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Adsorption of V on a hematite (0 0 0 1) surface and its oxidation: Monolayer coverage

Jin

Kim

et al. 2007

Surface Science

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“…PDOS of the surface atoms in these three monomer configurations are shown in Figure S3 (0001) substrate with the specified terminal ligands: [70]. Rudimentary assumptions about substrate-induced strain suggest that the dimers and chains might be more likely to "stretch apart" on the hematite surface as the lateral lattice parameter of the hematite cell (a = 5.01 Å) is 5.3% larger than that of sapphire (a = 4.76 Å).…”

Section: Resultsmentioning

confidence: 99%

Cation synergies affect ammonia adsorption over VOX and (V,W)OX dispersed on α-Al2O3 (0001) and α-Fe2O3 (0001)

McBriarty

Ellis

2016

Surface Science

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The catalytic behavior of oxide-supported metal oxide species depends on the nature of the support and the presence of co-catalysts. We use density functional theory (DFT) to explore the relationship between the structure and chemical behavior of vanadium oxide in light of its industrial use for the selective catalytic reduction of nitric oxide with ammonia (NO-SCR). The relative stabilities of dispersed VO X monomers, dimers, and long-chain oligomers on two model oxide support surfaces with similar structure but drastically different chemical behavior, α-Al 2 O 3 (0001) and α-Fe 2 O 3 (0001), are determined. The effect of added tungsten, known to promote NO-SCR, is also investigated on the relatively inert α-Al 2 O 3 (0001) support. We find that the adsorption behavior of NH 3 , representing the first step of the NO-SCR reaction, depends strongly on the VO X local structure. Protonation of NH 3 to NH 4 + over surface hydroxyls is energetically favorable over VO X-WO X dimers and VO X oligomers, which are stabilized by the reducible α-Fe 2 O 3 (0001) support.

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“…Exposure of the V films to atomic oxygen resulted in the formation of V 2 O 5 , and the reoxidation of the surface Fe [342]. In subsequent XSW studies [551], the authors demonstrated a clear link between the oxidation state of the V, and its position with respect to the iron-oxide substrate. Hydration (through exposure to air) also oxidises the V to V 5+ , although it can be reduced again by annealing at 773 K in H 2 [553].…”

Section: +mentioning

confidence: 93%

Iron oxide surfaces

Parkinson

2016

Surface Science Reports

501

463

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The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe 3 O 4 ), maghemite (γ-Fe 2 O 3 ), hematite (α-Fe 2 O 3 ), and wüstite (Fe 1-x O) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe 3 O 4 is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment, and because it is an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed.The best understood iron oxide surface at present is probably Fe 3 O 4 (100); the structure is known with a high degree of precision and the major defects and properties are well characterised. A major factor in this is that a termination at the Fe oct -O plane can be reproducibly prepared by a variety of methods, as long as the surface is annealed in 10 Such straightforward preparation of a monophase termination is generally not the case for other iron oxide surfaces. All available evidence suggests the oft-studied (√2×√2)R45° reconstruction results from a rearrangement of the cation lattice in the outermost unit cell in which two octahedral cations are replaced by one tetrahedral interstitial, a motif conceptually similar to well-known Koch-Cohen defects in Fe (0001) is the most studied hematite surface, but 2 difficulties preparing stoichiometric surfaces under UHV conditions have hampered a definitive determination of the structure. There is evidence for at least three terminations: a bulk-like termination at the oxygen plane, a termination with half of the cation layer, and a termination with ferryl groups. When the surface is reduced the so-called "bi-phase" structure is formed, which eventually transforms to a Fe 3 O 4 (111)-like termination. The structure of the bi-phase surface is controversial; a largely accepted model of coexisting Fe 1-x O and α-Fe 2 O 3 (0001) islands was recently challenged and a new structure based on a thin film of Fe 3 O 4 (111) on α-Fe 2 O 3 (0001) was proposed. The merits of the compet...

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Atomic-Scale View of Redox-Induced Reversible Changes to a Metal-Oxide Catalytic Surface: VO_x/α-Fe₂O₃(0001)

Cited by 19 publications

References 25 publications

Adsorption of V on a hematite (0 0 0 1) surface and its oxidation: Monolayer coverage

Adsorption of V on a hematite (0 0 0 1) surface and its oxidation: Monolayer coverage

Cation synergies affect ammonia adsorption over VOX and (V,W)OX dispersed on α-Al2O3 (0001) and α-Fe2O3 (0001)

Iron oxide surfaces

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