Reduction of copper oxides by UV radiation and atomic hydrogen studied by XPS

Fleisch, T. H.; Mains, Gilbert J.

doi:10.1016/0378-5963(82)90134-9

Cited by 135 publications

(79 citation statements)

References 21 publications

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“…Most probably, two last reactions proceed consequently. It should be also noted that the presented TPR data do not reflect a variation of original MS signals at the corresponding masses (m/z), but have been calculated from them using normalization by sensitivity factors [57] and taking into account the fact that a MS signal at the same mass (m/z) can be originated from different products. For instance, the signal at m/z ¼ 29 can belong both to methanol and to formaldehyde; signal at 28 -to CO, CO 2 and formaldehyde.…”

Section: Methanol Oxidation Over Coppermentioning

confidence: 99%

“…Among them are oxygen adsorbed at the copper surface, which gives the rise to an O1s feature at 529.7 eV, copper(I) oxide (530.4 eV), copper(II) oxide (529.6 eV), methoxy-(530.2 ± 0.2 eV) and formate-groups (531.4 ± 0.2 eV) [22,[56][57][58][59]. Selection between these species requires analysis of a whole set of XPS spectra: not only O1s and Cu2p, but also C1s and CuLVV Auger spectra should be analyzed.…”

Section: Methanol Oxidation Over Coppermentioning

confidence: 99%

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X-ray photoelectron spectroscopy as a tool for in-situ study of the mechanisms of heterogeneous catalytic reactions

2005

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An ESCALAB High Pressure photoelectron spectrometer specially designed by Vacuum Generators Co. (UK) for in-situ measurements at high pressures has been modified for adsorption and catalytic experiments. New construction of a gas cell, which serves to create a high-pressure zone, allows us to measure photoemission spectra in-situ at pressures up to 0.2-0.5 mbar and to use a sample holder with independent heating of a sample. This makes it possible to measure temperature programmed desorption and reaction spectra and, as a consequence, to characterize the catalytic properties simultaneously with the acquisition of X-ray photoelectron spectroscopy (XPS) data. Capabilities of the modified spectrometer are demonstrated by the examples of studies of CO and methanol adsorption on Pd(111) single crystal and methanol oxidation over Cu poly .The XPS study of high-pressure adsorption of CO on perfect and sputtered Pd (111) showed that raising the pressure has the same effect as decreasing the temperature. The CO coverage is increased due to adsorption of CO to weakly bound (on-top) state, which appears in addition to more strongly bound three-fold and bridged species. No indications of CO dissociation or carbonyl formation were found under the given experimental conditions (high pressure and sputtering-induced defects), provided that the CO gas was sufficiently clean.Two pathways of methanol decomposition to CH x,ads (x 3) and to CO ads was unambiguously identified, with their contribution being dependent on P and T. The decomposition to carbon-originated species had a small contribution in UHV conditions at room temperature, but became more significant at higher pressures and temperatures.Analysis of the distribution of the reaction products and surface species during methanol oxidation over copper in the submillibar pressure range showed that an increase in catalytic activity observed on heating the sample from 420 to 670 K is accompanied by transformation of the adlayer composition. At low temperatures, the surface is covered by methoxy-and, to a lesser extent, formate-groups. The active surface (T > 520 K) is metallic copper with two adsorbed oxygen species. The possible nature of these species is discussed.

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Section: Methanol Oxidation Over Coppermentioning

confidence: 99%

Section: Methanol Oxidation Over Coppermentioning

confidence: 99%

X-ray photoelectron spectroscopy as a tool for in-situ study of the mechanisms of heterogeneous catalytic reactions

2005

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“…Nevertheless, these oxides were easily reduced using ultraviolet light prior and during x-ray laser induced photoelectron spectroscopy. [20,21] Figure 4 presents the single-shot e-ToF photoemission spectra of the 3d valence band of static and laser heated ultra-thin polycrystalline Cu foil illuminated with 10 8 -10 9 x-ray laser photons. This sample is sufficiently thin to observe the transmitted x-ray laser beam simultaneously with the photoelectron signal.…”

Section: Resultsmentioning

confidence: 99%

Advancements in time-resolved x-ray laser induced time-of-flight photoelectron spectroscopy

et al. 2005

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Time-resolved soft x-ray photoelectron spectroscopy is used to probe the non-steady-state evolution of the valence band electronic structure of laser heated ultra-thin (50 nm) metal foils and bulk semiconductors. Single-shot soft x-ray laser induced time-of-flight photoelectron spectroscopy with picosecond time resolution was used in combination with optical measurements of the disassembly dynamics that have shown the existence of a metastable liquid phase in fs-laser heated metal foils persisting 4-5 ps. This metastable phase is studied using a 527 nm wavelength 400 fs laser pulse containing 0.3 -2.5 mJ laser energy focused in a large 500 x 700 µm 2 spot to create heated conditions of 0.2 -1.8 x 10 12 W cm -2 intensity. The unique LLNL COMET compact tabletop soft x-ray laser source provided the necessary high photon flux, highly monoenergetic, picosecond pulse duration, and coherence for observing the evolution of changes in the valence band electronic structure of laser heated metals and semiconductors with picosecond time resolution. This work demonstrates the continuing development of a powerful new technique for probing reaction dynamics and changes of local order on surfaces on their fundamental timescales including phenomena such as non-thermal melting, chemical bond formation, intermediate reaction steps, and the existence of transient reaction products.

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“…it did not reoxidize to Cu 2+ . [167] Comparing the reduced Cu oxides with LaTiO 3 -LaFeO 3 heterostructures, clear differences in reduction process were observed. No differences between in situ and ex situ measurements were observed for LaTiO 3 To study the effect of the template on the charge transfer in LaTiO 3 -LaFeO 3 heterostructures, the heterostructures were fabricated on SrTiO 3 and LaAlO 3 -LSAT.…”

Section: Fe Reductionmentioning

confidence: 99%

“…After He I exposure, the Fe was partially reduced to Fe 2+ , as shown in Reduction of cations in oxide crystals by X-ray exposure has been observed in previous studies. [167][168][169][170] An extensively studied example is the reduction of Cu in oxides. [167][168][169] Cu can completely reduce from Cu 2+ to metallic Cu when adsorbates are present at the surface.…”

Section: Fe Reductionmentioning

confidence: 99%

Reconstructions at complex oxide interfaces

Kleibeuker

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Reduction of copper oxides by UV radiation and atomic hydrogen studied by XPS

Cited by 135 publications

References 21 publications

X-ray photoelectron spectroscopy as a tool for in-situ study of the mechanisms of heterogeneous catalytic reactions

X-ray photoelectron spectroscopy as a tool for in-situ study of the mechanisms of heterogeneous catalytic reactions

Advancements in time-resolved x-ray laser induced time-of-flight photoelectron spectroscopy

Reconstructions at complex oxide interfaces

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