Characterization of oxide layers on Mg(0001) and comparison of H2O adsorption on surface and bulk oxides

Peng, Xiang; Barteau, Mark A.

doi:10.1016/0039-6028(90)90641-k

Cited by 111 publications

(71 citation statements)

References 29 publications

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“…Two main peaks can be seen here, which are attributed to emission from the 1π and 3σ orbitals of adsorbed OH groups. Similar spectra were observed for free OH radicals [31] and for OH groups adsorbed on other metal-oxides [32]. The features between -5 and -10 eV below E VAC are probably due to adsorbate induced changes of the substrate emission and to emission from the coadsorbed hydrogen species.…”

Section: Resultssupporting

confidence: 64%

Adsorption of water on FeO(111) and Fe3O4(111): identification of active sites for dissociation

Joseph

Kuhrs

Ranke

et al. 1999

Chemical Physics Letters

107

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The adsorption of water on epitaxial FeO(111) and Fe3O4(111) films structurally well characterized by STM and LEED was investigated with photoelectron and thermal desorption spectroscopy. On the FeO(111) surface terminated by a close-packed oxygen layer monomeric water species get physisorbed. On the Fe3O4(111) surface terminated by ¼ monolayer of Fe atoms located over a close-packed oxygen layer underneath water dissociates resulting in adsorbed OH groups. The OH saturation coverage corresponds to the number of surface Fe atoms, which is much larger than the surface defect concentrations. Therefore, the dissociation takes place at Fe sites exposed on the regular Fe3O4(111) surface, and the FeO(111) surface is chemically inert because no Fe sites exist thereon.

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Section: Resultssupporting

confidence: 64%

Adsorption of water on FeO(111) and Fe3O4(111): identification of active sites for dissociation

Joseph

Kuhrs

Ranke

et al. 1999

Chemical Physics Letters

107

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“…It is attributed to adsorbed OH species resulting from dissociation of water to form OH+H. The two peaks are due to the 1π and 3σ orbitals of OH as interpreted similarly for OH in NaOH [341] and on other metal-oxides [58,[342][343][344]. We also attribute the features between -5 and -10 eV to adsorbate induced changes in the substrate emission and possibly to emission from the coadsorbed H atom.…”

Section: (I) Electronic Structures Of Adsorbatesmentioning

confidence: 78%

“…Dissociative adsorption was observed on Ti 3+ rich Ar + -bombarded surfaces, such as Ti 2 O 3 (047) [352], TiO 2 (100) [353], SrTiO 3 (100) [354], whereas molecular adsorption was observed on the respective stoichiometric regular surfaces. On MgO(100) [343] and α-Fe 2 O 3 (0001) [136,349], water was found to dissociate both on regular and defective surfaces and a correlation between the defect concentration and amount of dissociative adsorption was found. On other oxides, the role of defects for the dissociative adsorption is not clear, because water dissociation occurs both on ordered and defective surfaces with a similar rates, as on V 2 O 3 (047) [135], TiO 2 (110) [355], TiO 2 (001) [356] and SnO 2 (110) [350].…”

Section: Discussionmentioning

confidence: 97%

Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers

Weiß

Ranke

2002

Progress in Surface Science

584

610

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Metal-oxide based catalysts are used for many important synthesis reactions in the chemical industry. A better understanding of the catalyst operation can be achieved by studying elemantary reaction steps on well-defined model catalyst systems. For the dehydrogenation of ethylbenzene to styrene in the presence of steam both unpromoted and potassium promoted iron-oxide catalysts are active. Here we review the work done over unpromoted single-crystalline FeO(111), Fe 3 O 4 (111) and α-Fe 2 O 3 (0001) films grown epitaxially on Pt(111) substrates. Their geometric and electronic surface structures were characterized by STM, LEED, electron microscopy and electron spectroscopic techniques. In an integrative approach, the interaction of water, ethylbenzene and styrene with these films was investigated mainly by thermal desorption and photoelectron emission spectroscopy. The adsorptiondesorption energetics and kinetics depend on the oxide surface terminations and are correlated to the electronic structures and acid-base properties of the corresponding oxide phases, which reveal insight into the nature of the active sites and into the catalytic function of semiconducting oxides in general. Catalytic studies, using a batch reactor arrangement at high gas pressures and post reaction surface analysis, showed that only α-Fe 2 O 3 (0001) containing surface defects is catalytically active, whereas Fe 3 O 4 (111) is always inactive. This can be related to the elementary adsorption and desorption properties observed in ultrahigh vacuum, which indicates that the surface chemical properties of the iron-oxide films do not change significantly across the "pressure-gap". A model is proposed according to which the active site involves a regular acidic surface sites and a defect site next to it. The results on metal-oxide surface chemistry also have implications for other fields, such as environmental science, biophysics and chemical sensors.-2 -"2kyEi9FYSQjBVrZxIPQ.FHIAC_WRa02_review.doc", Datum: 19.02.03

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“…The first species labeled γ saturates at 225 K with d/l e =0.43±0.03 and exhibits two broad peaks. We attribute them to the 1π and 3σ orbitals of OH δ--species formed by dissociation of water into OH δ-+H δ+ 48 , as observed on many other metal oxide surfaces [49][50][51][52][53][54] . The work function decreases by 0.75 eV, indicating that OH δ-species are adsorbed with the oxygen atom oriented towards the surface.…”

Section: Active Sites For Water Chemisorptionmentioning

confidence: 99%

Structure and reactivity of iron oxide surfaces

Shaikhutdinov¹,

Joseph²,

Kuhrs³

et al. 1999

Faraday Disc.

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Epitaxial films of different iron oxide phases and of potassium iron oxide were grown onto Pt(111) substrates and used for studying structure-reactivity correlations. The film morphologies and their atomic surface structures were characterized by scanning tunneling microscopy and low energy electron diffraction including multiple scattering calculations. The adsorption of water, ethylbenzene, and styrene was investigated by temperature programmed desorption and photoelectron spectroscopy. A dissociative chemisorption of water and a molecular chemisorption of ethylbenzene and styrene is observed on all oxides that expose metal cations in their topmost layers, whereas purely oxygen terminated FeO(111) monolayer films are chemically inert and only physisorption occurs. Regarding the technical styrene synthesis reaction which is performed over iron oxide based catalysts, we find a decreasing chemisorption strength of the reaction product molecule styrene if compared to ethylbenzene when going from Fe 3 O 4 (111) over α-Fe 2 O 3 (0001) to KFe x O y (111). Extrapolation of the adsorbate coverages to the technical styrene synthesis reaction conditions using the Langmuir isotherm for coadsorption suggests an increasing catalytic activity along the same direction. This result agrees with previous kinetic experiments performed at elevated gas pressures over the model systems studied here and over polycrystalline iron oxide catalyst samples. It indicates that the iron oxide surface chemistry does not change across the pressure-gap and that the model systems simulate technical styrene synthesis catalysts in a realistic way.

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Characterization of oxide layers on Mg(0001) and comparison of H2O adsorption on surface and bulk oxides

Cited by 111 publications

References 29 publications

Adsorption of water on FeO(111) and Fe3O4(111): identification of active sites for dissociation

Adsorption of water on FeO(111) and Fe3O4(111): identification of active sites for dissociation

Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers

Structure and reactivity of iron oxide surfaces

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