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Werner, Harald; Herein, Daniel; Schulz, G.; Wild, Ute; Schlögl, Robert

doi:10.1023/a:1019076415303

Cited by 74 publications

(35 citation statements)

References 18 publications

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“…Copper with its facile redox chemistry between oxide and metal, accessible at low and intermediate pressures [77] , is a suitable system for mechanistic studies of selectivity control. The fact that extensive kinetic oscillations in methanol oxidation were reported is an indication [78] that active Cu may exist both as an oxide and as a metal. In initial experiments it was found that clean copper without subsurface oxygen is inactive and that stoichiometric CuO (black) is also inactive, whereas red oxides (Cu 2 O) are active with maximum activity in transient regions where several phases co-existed due to kinetic instabilities [42,67] .…”

Section: Copper In Meoh Oxidationmentioning

confidence: 99%

“…It is thus of interest to know how the surface of a metallic catalyst responds with different surface phases according to the oxidizing or reducing nature of the gas environment, given by the partial pressures of O 2 and CH 3 OH. It can also be expected that an oscillatory change between oxide and metal, as observed at high pressures [78] and in forced modes at low pressures [77] , may give rise to a spatially inhomogeneous distribution of oxidation states, which could not coexist in thermodynamic equilibrium. In such a situation the usual practice of performing the reaction in a reactor chamber and later transferring, after cooling and evacuation, into the UHV chamber for analysis will not show the correct surface state but rather the equilibrated state [42] produced during evacuation.…”

Section: Copper In Meoh Oxidationmentioning

confidence: 99%

“…They are related with each other via a common reaction intermediate, namely formate, that was found to play a crucial role in surface science experiments [48,78,88,106] . In comparative studies on different supports [71,72] it was found that the redox properties of Cu play a critical role in steam reforming systems.…”

Section: Copper In Meoh Steam Reformingmentioning

confidence: 99%

See 2 more Smart Citations

Ambient pressure photoelectron spectroscopy: A new tool for surface science and nanotechnology

Salmerón

Schlögl

2008

Surface Science Reports

686

626

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Section: Copper In Meoh Oxidationmentioning

confidence: 99%

Section: Copper In Meoh Oxidationmentioning

confidence: 99%

See 1 more Smart Citation

Ambient pressure photoelectron spectroscopy: A new tool for surface science and nanotechnology

Salmerón

Schlögl

2008

Surface Science Reports

686

626

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“…With regards to its catalytic properties, the O/Cu system ͑i.e., oxidic nanostructures of Cu͒ is known to facilitate oxidation reactions, suggesting that it has potential as an economical alternative for the rare and high-cost noble metals in various catalytic systems. [3][4][5][9][10][11][12] Our recent study on the O/Cu͑111͒ system 13 has predicted that, under technical catalytic conditions of gas pressures and temperatures, the thermodynamically favored phase is that of the bulk oxide. Hence the oxide Cu 2 O should be considered as one of the key active catalytic phases in technologically relevant reactions.…”

Section: Introductionmentioning

confidence: 99%

Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide: First-principles study of bulk and surface properties ofCu2−δO

et al. 2009

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Native defects in cuprous oxide Cu 2 O are investigated by using first-principles calculations based on density-functional theory. Considering the formation of copper and oxygen vacancies, antisites and interstitials, and a copper split-vacancy complex defect, we analyze the electronic structure and calculate their respective formation energies as a function of the change in Fermi level under both copper-rich and oxygen-rich conditions. We find that, under both growth conditions, the defect with the lowest formation energy is the simple copper vacancy, followed by the copper split-vacancy complex. Both low-energy copper defects produce hole states at the top of the valence band, largely accounting for the p-type conductivity in this material. In spite of the creation of dangling bonds at the nearest-neighbor O atoms, these copper defects are found to be spin neutral. Under oxygen-rich conditions, oxygen interstitials have low formation energies and are found to exhibit a ferromagnetic ordering with a total magnetic moment of 1.38 B and 1.36 B at the octahedral and tetrahedral sites, respectively. Considering the possibility of native defect formation at the surface of this material, we investigate the relative stability of both low-and high-index copper-oxide surfaces by comparing their surface free energies as a function of the change in oxygen chemical potential. Using the technique of ab initio atomistic thermodynamics, we then correlate the dependence of the calculated Gibbs free-surface energy as a function of oxygen pressure and temperature via the oxygen chemical potential. We identify two lowenergy surface structures, namely, Cu 2 O͑110͒ : CuO and Cu 2 O͑111͒-Cu CUS , with the former marginally more stable for oxygen-rich conditions and the latter more stable for oxygen-lean ͑or copper-rich͒ conditions. Cu 2 O͑110͒ : CuO is calculated to be nonmagnetic and Cu 2 O͑111͒-Cu CUS is calculated to be a ferromagnetic ordering, with a total magnetic moment of 0.91 B per defect. With the results for both bulk and surface native defects, we find that under oxygen-lean conditions, a ferromagnetic behavior could be attributed mainly to copper vacancy formation in the ͑111͒ surface of Cu 2 O while under oxygen-rich conditions, low-energy bulk oxygen interstitial defects induce a ferromagnetic character in the same material. This highlights the complementary role of bulk and surface native magnetic defects under different pressure and temperature conditions, especially at the nanoparticle scale where surface properties dominate.

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“…[7][8][9][10][11][12][13][14][15][16] Different in situ techniques were applied in order to identify the active surface phases on polycrystalline Cu at higher pressure (mbar range). [17][18][19][20][21][22][23][24][25][26] Cu(110) surfaces were investigated with temperatureprogrammed desorption (TPD), molecular beam techniques, low energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM). 7,8,[10][11][12]15,[27][28][29][30] These techniques were typically applied under non-stationary conditions using sequential dosing and temperature-programmed experiments.…”

Section: Introductionmentioning

confidence: 99%

Adsorbate coverages and surface reactivity in methanol oxidation over Cu(110): An in situ photoelectron spectroscopy study

Günther

Zhou

Hävecker

et al. 2006

The Journal of Chemical Physics

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The adsorbate species present during partial oxidation of methanol on a Cu(110) surface have been investigated in the 10 -5 mbar range with in situ x-ray photoelectron spectroscopy (XPS) and rate measurements. Two reaction intermediates were identified, methoxy with a C 1s binding energy (BE) of 285.4 eV and formate with a C 1s BE of 287.7 eV. The c(2x2) overlayer formed under reaction conditions is assigned to formate. Two states of adsorbed oxygen were found characterized by O 1s BE's of 529.6 and 528.9 eV, respectively. On the inactive surface present at low T around 300 -350 K formate dominates while methoxy is almost absent. Ignition of the reaction correlates with a decreasing formate coverage. A large hysteresis of ≈ 200 K width occurs in T-cycling experiments whose correlation with adsorbate species was studied with varying oxygen and methanol partial pressures. The two branches of the hysteresis differ mainly in the amount of adsorbed oxygen, the methoxy species and a carbonaceous species. Methoxy covers only a minor part of the catalytic surface reaching at most 20%. Above 650 K the surface is largely adsorbate free.

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Cited by 74 publications

References 18 publications

Ambient pressure photoelectron spectroscopy: A new tool for surface science and nanotechnology

Ambient pressure photoelectron spectroscopy: A new tool for surface science and nanotechnology

Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide: First-principles study of bulk and surface properties ofCu2−δO

Adsorbate coverages and surface reactivity in methanol oxidation over Cu(110): An in situ photoelectron spectroscopy study

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