Water adsorption on the (001) plane of Fe2O3: An XPS, UPS, Auger, and TPD study

Hendewerk, M.; Salmerón, Miquel; Somorjai, Gábor A.

doi:10.1016/0039-6028(86)90500-5

Cited by 77 publications

(33 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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: 96%

See 1 more Smart Citation

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

Weiß

Ranke

2002

Progress in Surface Science

584

610

View full text Add to dashboard Cite

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

show abstract

Section: Discussionmentioning

confidence: 96%

“…Water adsorption studies on metal-oxide surfaces were initiated by work on its photocatalytic decomposition on TiO 2 [348], followed by investigations on other oxides and ionic compounds [5,338,349,350]. Molecular adsorption mostly occurs via the lone-pair of the O atom to an acidic surface site [58].…”

Section: Discussionmentioning

confidence: 99%

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

Weiß

Ranke

2002

Progress in Surface Science

584

610

View full text Add to dashboard Cite

show abstract

“…The interaction of water with α-Fe 2 O 3 (0001) surfaces has been studied both experimentally [413][414][415][416], and theoretically [416][417][418][419][420]. Kurtz and Heinrich [414] determined that water adsorbed dissociatively on an α-Fe 2 O 3 (0001) surface prepared by sputtering and 1100 K UHV annealing for pressures over 10 -5 torr, while the XPS study of Liu et al [349] suggested a threshold for hydroxylation at 10 -4 torr (both studies conducted at room temperature).…”

Section: H 2 O/ α-Fe 2 O 3 (0001)mentioning

confidence: 99%

Iron oxide surfaces

Parkinson

2016

Surface Science Reports

501

463

View full text Add to dashboard Cite

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...

show abstract

“…For NiO(100), Cr 2 O 3 (111) [4] and TiO 2 (110) [5] it was clearly shown that dissociative adsorption of water only takes place at defects and not at regular surface sites. No clear picture still has evolved for the Fe 2 O 3 (0001) surface [6][7][8] and many other surfaces, where dissociation seems to take place on regular surface areas as well as at defect sites. On Al 2 O 3 (0001) single crystal surfaces terminated by Al atoms [9] water dissociates on the regular surface areas [10], whereas thin epitaxial films terminated by O atoms are chemically inert [11].…”

Section: Introductionmentioning

confidence: 99%

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

View full text Add to dashboard Cite

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.

show abstract

Water adsorption on the (001) plane of Fe2O3: An XPS, UPS, Auger, and TPD study

Cited by 77 publications

References 13 publications

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

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

Iron oxide surfaces

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

Contact Info

Product

Resources

About