Catalytic Oxidation of Ethene on Polycrystalline Palladium: Influence of the Oxidation State of the Surface

Unterberger, Werner; Gabasch, Harald; Hayek, K.; Klötzer, Bernhard

doi:10.1007/s10562-005-7428-z

Cited by 13 publications

(18 citation statements)

References 21 publications

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“…More detailed information about the composition and further reaction of CH x overlayers was obtained in a high-pressure study by Morkel et al [22], with help of vibrational sum frequency generation (SFG) and X-ray photoelectron spectroscopy (XPS). Some of the present authors observed that polycrystalline palladium exhibits its highest selectivity for partial oxidation of ethene to acetic acid at about 423 K [23], in the temperature range where ethylidyne mainly decomposes towards surface-adsorbed carbon atoms [18]. In [23] it was also shown that a pre-treatment of the Pd surface with 6 mbar ethene at 493 K, resulting in massive surfacenear carbon accumulation, markedly enhanced the selectivity toward acetic acid.…”

Section: Introductionsupporting

confidence: 52%

“…Some of the present authors observed that polycrystalline palladium exhibits its highest selectivity for partial oxidation of ethene to acetic acid at about 423 K [23], in the temperature range where ethylidyne mainly decomposes towards surface-adsorbed carbon atoms [18]. In [23] it was also shown that a pre-treatment of the Pd surface with 6 mbar ethene at 493 K, resulting in massive surfacenear carbon accumulation, markedly enhanced the selectivity toward acetic acid. The formation of a subsurface PdC phase has also been shown to induce improved selectivity in pentyne hydrogenation toward pentene by inhibiting bulk-to-surface hydrogen diffusion [24].…”

Section: Introductionsupporting

confidence: 52%

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Ethene Oxidation on Pd(111): Kinetic Hysteresis Induced by Carbon Dissolution

et al. 2007

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The catalytic oxidation of ethene was studied on Pd(111) in the 10−7–10−6 mbar pressure range by a molecular beam TPR hysteresis experiment between 400 K and 1,000 K. Two important effects were identified: the reaction-blocking effect of a dense chemisorbed adlayer of oxygen and the promotional effect of dissolved carbon segregating back to the surface and efficiently reducing the adsorbed oxygen. A strong dependence of the catalytic activity on the oxygen partial pressure is explained by the inhibiting effect of oxygen adsorption; high oxygen pressures in fact extinguish the reaction. The presence of oxygen-free metal surface area, where ethene can dissociate, is necessary for high activity. During heating the highest activity is observed at T ∼ 620 K, where a combination of oxygen clean-off by carbon segregating back to the surface is combined with a high ethene adsorption rate, thus forming additional reaction sites and additional reaction products. During heating this carbon-induced clean-off of O(ad) is very efficient because the dissolved C atoms rather accumulate in the surface-near region and largely segregate back to the surface at T > 600 K. In contrast, during cooling from higher temperatures a high surface-near carbon bulk concentration does not build up because the bulk mobility of C atoms is also high and the faster diffusion of C into deeper layers counteracts carbon enrichment in the surface-near metal bulk. This effect favours a higher oxygen surface coverage and a stronger deactivation during cooling. If the carbon loading of the surface-near region was increased by decomposition of clean ethene prior to the reaction experiment, the promotional effect during the heating cycle was strongly enhanced, but the cooling cycle showed no memory of the C presaturation. Generally, the observed hysteresis effects stem from an interplay of combined oxygen site blocking and carbon diffusion effects

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Section: Introductionsupporting

confidence: 52%

Section: Introductionsupporting

confidence: 52%

Ethene Oxidation on Pd(111): Kinetic Hysteresis Induced by Carbon Dissolution

et al. 2007

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“…A kinetic study of ethane oxidation on PdO formed on a polycrystalline Pd foil performed recently in our group [33] has shown that on stoichiometric PdO, this reaction starts with a partial reduction of the surface towards the metallic state which is responsible for a delayed onset of the reaction. Therefore, we now focused on the behavior of the PdO phase upon a reductive treatment and, in comparison, upon a simple annealing treatment.…”

Section: Bstability Of Pdo Under Reductive and Annealing Conditionsmentioning

confidence: 99%

“…On the other hand, we shall focus on the differences in reduction by CO and decomposition in He atmosphere, respectively, in close correlation to previous experiments on ethane oxidation. [33] EXPERIMENT A high-vacuum chamber (base pressure of 10 -4 Pa) was used to prepare the SiO 2 -supported Pd catalysts. Pd particles (nominal thickness of 0.6 nm) were grown by electron-beam deposition at 623 K on vacuum-cleaved NaCl(001) single crystal surfaces.…”

Section: Introductionmentioning

confidence: 99%

Growth and decomposition of aligned and ordered PdO nanoparticles

Penner

Wang

Jenewein

et al. 2006

The Journal of Chemical Physics

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The formation, thermal decomposition, and reduction of small PdO particles were studied by high-resolution transmission electron microscopy and selected area electron diffraction. Welldefined Pd particles (mean size of 5-7 nm) were grown epitaxially on NaCl (001) surfaces and subsequently covered by a layer of amorphous SiO 2 (25 nm), prepared by reactive deposition of SiO in 10 -2 Pa O 2 . The resulting films were exposed to molecular O 2 in the temperature range of 373-673 K, and the growth of PdO was studied. The formation of a PdO phase starts at 623 K and is almost completed at 673 K. The high-resolution experiments suggest a topotactic growth of PdO crystallites on top of the original Pd particles. Subsequent reaction of the PdO in 10 mbar CO for 15 min and thermal decomposition in 1 bar He for 1 h were also investigated in the temperature range from 373 to 573 K. Reductive treatments in CO up to 493 K do not cause a significant change in the PdO structure. The reduction of PdO starts at 503 K and is completed at 523 K. In contrast, PdO decomposes in 1 bar He at around 573 K. The mechanism of PdO growth and decay is discussed and compared to results of previous studies on other metals, e.g., on rhodium.

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“…The influence on the catalytic properties of carbon residing in the subsurface region was described previously [14][15][16]. Since these are all ex situ studies the question of stability of intermediates is an issue.…”

Section: -Pentyne Hydrogenation On Pd Based Catalystsmentioning

confidence: 99%

The role of carbon species in heterogeneous catalytic processes: an in situ soft x-ray photoelectron spectroscopy study

Vass

Hävecker

Zafeiratos

et al. 2008

J. Phys.: Condens. Matter

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High pressure X-ray photoelectron spectroscopy (XPS) is used to characterize heterogeneous catalytic processes. The success of the new technique based on the possibility to correlate the catalytic activity and the electronic structure of an active surface. The dynamic character of a catalyst surface can be demonstrated impressively by this technique. In this contribution the basics of high pressure XPS will be discussed. Three examples of heterogeneous catalytic reactions are presented in this contribution. The selective hydrogenation of 1-pentyne over Pd based catalysts and the dehydrogenation of n-butane and the oxidation of ethylene over V based catalysts. It is shown, that the formation of subsurface carbons plays an important role in all the examples. The incorporated carbon changes the electronic structure of the surface and so controls the selectivity of the reaction. A change of the educts in the reaction atmosphere induces modifications of the electronic surface structure of the operation catalysts.

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Catalytic Oxidation of Ethene on Polycrystalline Palladium: Influence of the Oxidation State of the Surface

Cited by 13 publications

References 21 publications

Ethene Oxidation on Pd(111): Kinetic Hysteresis Induced by Carbon Dissolution

Ethene Oxidation on Pd(111): Kinetic Hysteresis Induced by Carbon Dissolution

Growth and decomposition of aligned and ordered PdO nanoparticles

The role of carbon species in heterogeneous catalytic processes: an in situ soft x-ray photoelectron spectroscopy study

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