Hydroxyl groups on oxide surfaces: NiO(100), NiO(111) and Cr2O3(111)

Cappus, D.; Xu, Chen; Ehrlich, D.; Dillmann, B.; Ventrice, Carl A.; Al‐Shamery, Katharina; Kuhlenbeck, Helmut; Freund, Hans‐Joachim

doi:10.1016/0301-0104(93)80031-4

Cited by 235 publications

(153 citation statements)

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“…For this reason, water dissociation on metals is often observed only when O is preadsorbed [58], as was observed first on Pt(111) [351]. On non-polar oxide surfaces, such as CoO(100) [342] and NiO(100) [64,344] dissociative adsorption is found to occur only at defects, whereas the corresponding regular surface areas are inert. 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.…”

Section: Discussionmentioning

confidence: 93%

“…Polar surface planes can be stabilized by hydroxylation, because it reduces excess surface charge and, therefore, the electrostatic surface dipole moment (see Section 2.8). Upon dehydroxylation, these surface planes reconstruct, in order to establish a more stable configuration [64][65][66].…”

Section: Adsorption Processmentioning

confidence: 99%

“…However, there is not much direct experimental evidence for the higher reactivity of surface defect sites of metal-oxides. Studies on single-crystalline NiO (100) and (111) surfaces revealed water to dissociatively adsorb at atomic defect sites [64,68], and it is well-known that completely hydroxylized oxides are not active, unless they get dehydroxylated, so that highly unsaturated sites are exposed again [2].…”

Section: Adsorption Processmentioning

confidence: 99%

“…• by adsorption of charged species, such as protons or OH groups, as observed on NiO(111) and Cr 2 O 3 (0001) surfaces [64];…”

Section: Energetics Of Metal-oxide Surfacesmentioning

confidence: 99%

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

Weiß

Ranke

2002

Progress in Surface Science

579

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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Section: Discussionmentioning

confidence: 93%

Section: Adsorption Processmentioning

confidence: 99%

Section: Adsorption Processmentioning

confidence: 99%

“…• by adsorption of charged species, such as protons or OH groups, as observed on NiO(111) and Cr 2 O 3 (0001) surfaces [64];…”

Section: Energetics Of Metal-oxide Surfacesmentioning

confidence: 99%

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

Weiß

Ranke

2002

Progress in Surface Science

579

610

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“…Polar oxide surfaces are of growing technological importance in a wide range of applications due to their particular properties. These range through such diverse applications as catalysis [25], the newest giant magnetoresistive devices [26] (based on the polar (111) surface of NiO), and in a variety of semiconductor devices [27]. The results and methodology of the current study are therefore of significance in a wide range of applications.…”

mentioning

confidence: 94%

Stability of Polar Oxide Surfaces

et al. 2001

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The structures of the polar surfaces of ZnO are studied using ab initio calculations and surface x-ray diffraction. The experimental and theoretical relaxations are in good agreement. The polar surfaces are shown to be very stable; the cleavage energy for the (0001)-Zn and ͑0001 ͒-O surfaces is 4.0 J͞m 2 comparable to 2.32 J͞m 2 for the most stable nonpolar (1010) surface. The surfaces are stabilized by an electronic mechanism involving the transfer of 0.17 electrons between them. This leads to 2D metallic surface states, which has implications for the use of the material in gas sensing and catalytic applications. DOI: 10.1103/PhysRevLett.86.3811 PACS numbers: 68.03.Cd, 68.35.Bs, 73.20.At The ionic model has provided the basis for our understanding of the very wide range of physical phenomena displayed by "ionic" crystals [1][2][3][4]. The model underpins our understanding of, for instance; cohesive properties, complex dielectric and optical response, and novel magnetic and electronic behavior including giant magnetoresistance and superconductivity [2]. One of the interesting consequences of the ionic model is that certain "polar" surfaces of ionic crystals will have a surface energy that diverges with sample size due to the generation of a macroscopic electrostatic field across the crystal. A definitive description of this behavior and the classification scheme which is now widely used were given by Tasker in 1979 [5]. Remarkably, a large number of naturally occurring materials have morphologies which display polar surfaces. In recent years a variety of stabilizing mechanisms have been demonstrated to operate at particular surfaces which typically involve the quenching of the macroscopic field either through the reconstruction of the surface, or the presence of adsorbates on the surface [3]. However, in some cases it appears that clean, unreconstructed surfaces are stable, at variance with Tasker's conclusions. A notable example is zincite (ZnO). A possible mechanism for the stability of these systems is a rearrangement of the electronic structure resulting in an effective charge transfer between the polar surfaces removing the macroscopic field which would otherwise be present. To date, no first principles investigation of such a phenomenon has been performed, although semiempirical calculations on SrTiO 3 indicate that such a mechanism might be operating [6,7]. Recently, similar effects have also been observed for thin film ionic materials grown on metallic substrates such as NaCl(111) on aluminum [8].ZnO crystallizes in the Wurtzite structure which does not have a center of inversion. Consequently, when the crystal is cleaved normal to the c axis in a manner which breaks the fewest interatomic bonds, two different polar surfaces are formed on opposite sides of the crystal, each having only one type of ion in its outermost plane. Thus, such a system may be considered to be a "slab" of material with the Zn cation outermost for the (0001)-Zn surface and the O anion outermost on the ͑0001͒-O surface. In orde...

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Ultrathin Oxide Films

Freund

Goodman

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Magnesium Oxide Mg O (100)/ Mo (100) Mg O (100)/ Ag (100) Mg O (111)/ Mo (110) Nickel Oxide Ni O (100)/ Ni (100), Mo (100) Ni O (111)/ Ni (111) Alumina Alumina/ Ni Al (110) Alumina/ Ni 3 Al (111) Al 2 O 3 (111)/ Ta (110) Al 2 O 3 (111)/ Mo (110) and Cu / Al 2 O 3 (111)/ Mo (110) Silica Si O 2 / Mo (110) Si O 2 / Mo (211) Cu / Si O 2 / Mo (110) Pd / Si O 2 / Mo (110) Au / Si O 2 / Mo (211) and Au / Ti O 2 / Si O 2 / Mo (211) Titania Ti x O y / Mo (100), Mo (110), Pt (111), Ni (110), W (100) Au / Ti O x / Mo (211) Chromia Cr 2 O 3 (111)/ Cr (11O) Vanadia Vanadium Sesquioxide Iron oxides Fe O / Pt (111), Fe 2 O 3 (0001)/ Pt (111), Fe 3 O 4 (001)/ Pt (111) Pd , Au on Iron Oxides Niobia Molybdenum Oxide Ceria Binary Oxides Ni O / Mg O , Ni O / Ca O , Mg O / Ni O , Ca O / Ni O / Mo (100) Conclusions Acknowledgments

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Hydroxyl groups on oxide surfaces: NiO(100), NiO(111) and Cr2O3(111)

Cited by 235 publications

References 29 publications

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

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

Stability of Polar Oxide Surfaces

Ultrathin Oxide Films

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