Kinetics of Palladium Oxidation in the mbar Pressure Range: Ambient Pressure XPS Study

Zemlyanov, Dmitry; Klötzer, Bernhard; Gabasch, Harald; Smeltz, Andrew; Ribeiro, Fabio H.; Zafeiratos, Spyridon; Teschner, Detre; Schnörch, Péter; Vass, Elaine M.; Hävecker, Michael; Knop‐Gericke, Axel; Schlögl, Robert

doi:10.1007/s11244-013-0052-z

Cited by 39 publications

(45 citation statements)

References 37 publications

(72 reference statements)

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“…Two other peaks at 529.0 and 529.6 eV observed at 373 K can be attributed to different C x O y adsorbed species as well. Similar values of the O1s binging energy are also observed for adsorbed and dissolved atomic oxygen species and for Pd 5 O 4 surface oxide [36][37][38]. However, the presence of large amounts of dissolved oxygen species is unlikely because the characteristic features of the PdC x phase are clearly observed in , and O1s (c) core-level spectra obtained during stepwise heating (spectra 1, 2, 3, and 4) and subsequent cooling (spectra 5, 6, and 7) of Pd (5 5 1) in the reaction mixture (R = 10).…”

Section: Resultssupporting

confidence: 78%

“…Correspondently, the O1s peaks at 529.0 and 529.6 eV can be attributed to oxygen in the surface oxide. According to literature data [36,37], oxygen atoms with different local environment in the Pd 5 O 4 structure on Pd(1 1 1) are characterized by the O1s binding energies of 528.9-529.0, 529.5-529.6, and 530.4 eV. The dissolved oxygen usually forms at higher temperatures [36].…”

Section: Resultsmentioning

confidence: 99%

“…According to literature data [36,37], oxygen atoms with different local environment in the Pd 5 O 4 structure on Pd(1 1 1) are characterized by the O1s binding energies of 528.9-529.0, 529.5-529.6, and 530.4 eV. The dissolved oxygen usually forms at higher temperatures [36]. No bulk PdO was formed under all conditions used since we did not observe its characteristic peak at 336.8 eV in the Pd3d 5/2 spectra [43].…”

Section: Resultsmentioning

confidence: 99%

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Oxidation of propylene over Pd(5 5 1): Temperature hysteresis induced by carbon deposition and oxygen adsorption

et al. 2015

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a b s t r a c tThe oxidation of propylene over a Pd(5 5 1) single crystal surface has been studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed reaction spectroscopy during both heating and cooling in various oxygen/propylene mixtures. In all the experiments, the partial pressure of propylene was approximately 1 × 10 −7 mbar and the partial pressure of oxygen was varied to achieve molar oxygen/propylene ratios of 1, 3, 10, and 100. Under all these conditions, we observed a temperature hysteresis: temperature dependences of the catalyst activity and product distribution were different during heating and cooling. It was shown that the temperature hysteresis was due to concurrent accumulation of carbon and oxygen atoms on the palladium surface. At low temperatures, a high concentration of carbonaceous deposits detected by XPS resulted in a low catalytic activity due to blocking of the palladium surface. Increasing temperature led to full dehydrogenation of the carbonaceous species and dissolution of carbon atoms into subsurface palladium layers. As a result, even under oxygen-rich conditions, the formation of a PdC x phase was detected by XPS at 373 K. This process had no influence on the selectivity in the oxidation of propylene at least under UHV conditions. A shift of selectivity toward CO 2 was found to result from an increase in the oxygen concentration on the palladium surface. The state with a low catalytic activity in the oxidation of propylene was associated with palladium in the metallic state covered by carbon deposits. The high-active state of palladium was associated with palladium in the metallic state with a high concentration of chemisorbed oxygen and a moderate concentration of a surface oxide. Bulk PdO was not detected by XPS under all conditions used.

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Section: Resultssupporting

confidence: 78%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Oxidation of propylene over Pd(5 5 1): Temperature hysteresis induced by carbon deposition and oxygen adsorption

et al. 2015

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“…Dedicated environmental TEMs (ETEM) can allow high resolution imaging and spectroscopy in a gaseous environment, but are limited to mbar-range pressures [3][4][5][6]. To simulate operando conditions for many relevant systems, higher pressures are needed: the decomposition temperature of PdO in O 2 , for instance, changes by nearly 300 degrees between 1 mbar and 1 atm [7][8][9]. There have been several reports of greater-than-atmospheric pressures using customized stages in which the gas is contained between two semi-transparent windows, typically a pair of amorphous SiN membranes separated by less than 100 mm [10][11][12][13][14][15][16][17]22,23].…”

Section: Introductionmentioning

confidence: 99%

A method for measuring the local gas pressure within a gas-flow stage in situ in the transmission electron microscope

et al. 2015

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Environmental transmission electron microscopy (TEM) has enabled in situ experiments in a gaseous environment with high resolution imaging and spectroscopy. Addressing scientific challenges in areas such as catalysis, corrosion, and geochemistry can require pressures much higher than the ∼20 mbar achievable with a differentially pumped environmental TEM. Gas flow stages, in which the environment is contained between two semi-transparent thin membrane windows, have been demonstrated at pressures of several atmospheres. However, the relationship between the pressure at the sample and the pressure drop across the system is not clear for some geometries. We demonstrate a method for measuring the gas pressure at the sample by measuring the ratio of elastic to inelastic scattering and the defocus of the pair of thin windows. This method requires two energy filtered high-resolution TEM images that can be performed during an ongoing experiment, at the region of interest. The approach is demonstrated to measure greater than atmosphere pressures of N2 gas using a commercially available gas-flow stage. This technique provides a means to ensure reproducible sample pressures between different experiments, and even between very differently designed gas-flow stages.

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“…APXPS is also very useful to follow up almost all the thermodynamic stability regions spanning from UHV to ambient pressure. Identifying and characterizing different oxides including metastable ones in a palladium‐oxygen system was possible . During the oxidation of palladium, a two‐dimensional surface oxide, a subsurface oxide, and bulk oxide form were identified, depending on the temperature and pressure.…”

Section: Applications Of Apxpsmentioning

confidence: 99%

Ambient Pressure Photoelectron Spectroscopy: Opportunities in Catalysis from Solids to Liquids and Introducing Time Resolution

2018

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Photoelectron spectroscopy is an excellent technique to explore chemically complex systems in catalysis. However, due to a small mean free path of photoelectrons in gas, liquid, and solid media, the study of the gas–solid, liquid–gas, solid–liquid interfaces, as well as liquid homogeneous systems are a serious challenge. With differentially pumped analyzers this limitation ceases to exist and no longer restricts photoelectron spectroscopy only to ultra‐high vacuum conditions. Presently, photoemission studies at tens of mbar of pressure are possible. To reach atmospheric pressure and even higher, membrane‐covered closed cells have been developed. Graphene membranes are impermeable to molecules and almost transparent to photoelectrons. They are used as a pressure barrier between the enclosed cell at atmospheric pressure and the electron analyzer at vacuum while allowing transmission of photoelectrons. By accessing to atmospheric pressure range, with this kind of cell, photoemission studies will become a versatile in situ and operando tool for catalysis. Studies involving liquids in static conditions are an important aspect in this direction, which can be extended to homogeneous catalytic systems. Liquids are presently accessible using micro‐jets. Another aspect which is of paramount interest to investigate catalysts is time resolution. By improving the time resolution of photoemission measurements to the sub‐second regime it is possible to follow the kinetic changes that are crucial of a catalytic reaction, the changes that occur during catalyst pretreatment and activation, and notably to differentiate active species from spectator ones, which may be the dominating species in a classical experiment.

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Kinetics of Palladium Oxidation in the mbar Pressure Range: Ambient Pressure XPS Study

Cited by 39 publications

References 37 publications

Oxidation of propylene over Pd(5 5 1): Temperature hysteresis induced by carbon deposition and oxygen adsorption

Oxidation of propylene over Pd(5 5 1): Temperature hysteresis induced by carbon deposition and oxygen adsorption

A method for measuring the local gas pressure within a gas-flow stage in situ in the transmission electron microscope

Ambient Pressure Photoelectron Spectroscopy: Opportunities in Catalysis from Solids to Liquids and Introducing Time Resolution

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