Interaction of NO and O2 with Pd(111) surfaces. II

Conrad, H.; Ertl, G.; Küppers, J.; Latta, E.E.

doi:10.1016/0039-6028(77)90305-3

Cited by 308 publications

(138 citation statements)

References 18 publications

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“…The apparent kinetic constant increases with increasing catalyst potential, probably indicating the creation of free sites for methane adsorption ,due to the weakening of the metal-oxygen bond (electron acceptor). The strong bonding of oxygen on the Pd surface, well known from literature [47][48][49], is reflected on the practically zero order kinetics with respect to oxygen partial pressure shown on Fig. 6, for oxygen to methane ratios higher than 1.…”

Section: Kineticsmentioning

confidence: 89%

Electrochemical promotion of CH4 oxidation on Pd

Giannikos

Frantzis

Pliangos

et al. 1998

Ionics

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Abstract. The effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA effect) or Electrochemical Promotion (EP) was used to promote the methane oxidation reaction to CO2 and H20 over Pd polycrystalline films interfaced with yttria-stabilized zirconia in galvanic cells of the type: CH4, O2, CO 2, Pd/YSZ/Au, CH 4, 02, CO2It was found that by applying positive potentials or currents and thus, supplying O 2-onto the catalyst surface, up to 90-fold increases in CH 4 oxidation catalytic rate can be obtained. The induced changes in catalytic rate were two orders of magnitude higher than the corresponding rate of ion transfer to the catalyst-electrode surface, i.e. faradaic efficiency A values above 100 can be attained. The reaction exhibits electrophobic behavior under the experimental conditions of the investigation. The results can be rationalized on the basis of the theoretical considerations invoked to explain NEMCA behavior, i.e. the effect of changing work function on chemisorptive bond strengths of catalytically active electron donor or acceptor adsorbates.

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Section: Kineticsmentioning

confidence: 89%

Electrochemical promotion of CH4 oxidation on Pd

Giannikos

Frantzis

Pliangos

et al. 1998

Ionics

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“…The picture arising from this work is that for temperatures T > 200 K oxygen adsorption is dissociative and for a coverage of θ ) 0.25 monolayer (ML) a (2 × 2) ordered overlayer is formed, where the oxygen adatoms occupy the 3-fold face-centered cubic (fcc) hollow sites. At higher coverages, on-surface adsorption seems to compete with the formation of a (surface) oxide, and depending on the preparation conditions, a ( 3 × 3)R30°, 6 a (1 × 1), 7,11 and a so-called "complex" 6,13 structure have been observed by lowenergy electron diffraction (LEED). In a combined experimental and density functional theory (DFT) study, the atomic structure behind the "complex" LEED pattern was recently identified as a surface oxide containing about 0.7 ML of oxygen.…”

Section: Introductionmentioning

confidence: 99%

Oxygen Overlayers on Pd(111) Studied by Density Functional Theory

2004

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By use of density-functional theory we analyze the on-surface adsorption of oxygen on Pd(111) for coverages up to 1 monolayer and compare the results with corresponding data for the other late 4d transition metals, namely, Ru, Rh, and Ag. Besides the known effect of the continued d-band filling on the oxygen-metal bond strength, we also discern trends in the adsorption geometries, work functions, and electron density of states. The repulsive lateral interactions in the overlayer give rise to a pronounced reduction of the adsorption energy at higher on-surface coverages. In fact, for oxygen coverages θ > 0.5 monolayers, the thermodynamic equilibrium phase of O/Pd(111) is known to be a surface oxide. The calculations reported in this paper show that on-surface adlayers at such higher coverages, that may exist as metastable phases, still possess qualitatively the same surface chemical bond as that which is found at low coverages. The dependence of the surface relaxation on oxygen coverage exhibits some unexpected behavior.

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“…These peaks at 2.7 and 14.8 eV originate from 2π and 4σ orbitals of NO molecules, respectively, as determined by several authors [13][14][15][16]. With increasing annealing temperature, the two peaks of 1π+5σ orbitals gradually decrease and the peaks at 9.4 and 11.2 eV disappear at 423 K and 393 K, respectively.…”

Section: Almentioning

confidence: 62%

“…The NO dissociation takes place preferentially at the step sites, because the peak of 1π+5σ orbitals of NO adsorbed at the step sites disappears at a lower temperature than does the peak of NO adsorbed on the terrace sites. The peak at 6.0 eV becomes broad above 423 K and disappears at 623 K. Conrad et al observed the peaks at 6.4, 10.6, and 13.5 eV below E F , which are due to the formation of PdO on Pd(111) after exposure to 10 −6 Torr NO at 900 K [14]. The broadening of the peak at 6.0 eV is indicative of the formation of surface oxide (PdO).…”

Section: Almentioning

confidence: 98%

Influence of Step Sites on Thermal Behavior of NO on Stepped Pd(112) Studied by AES, XPS and UPS

Irokawa

Ito

Okada

et al. 2009

e-J. Surf. Sci. Nanotechnol.

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The adsorption and thermal dissociation of nitric oxide on a stepped Pd(112) surface has been investigated by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). NO undergoes molecular adsorption on a stepped Pd(112) surface at 300 K. With increasing temperature, some NO adsorbed on the surface desorbs molecularly and the remaining NO starts to dissociate into nitrogen and oxygen. The NO dissociation takes place preferentially at the step sites. All NO molecules adsorbed on the surface dissociate above 423 K. Nitrogen desorbs from the surface above 700 K but oxygen exists on the surface or subsurface. UPS results show that the peak at 11.2 eV below Fermi level (EF), originating from the 1π+5σ orbital of NO adsorbed on step sites of Pd (112), disappear at a lower temperature than does the peak of NO adsorbed on terrace sites. This indicates that NO molecules adsorbed on step sites are dissociated at a temperature lower than those at terrace sites. The dissociation activity of NO on Pd(112) is stronger than on the (111) and (110) surfaces, but weaker than on the (100) surface. The order of the dissociation activity is Pd(100) > Pd(112) > Pd(111) > Pd(110).

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Interaction of NO and O2 with Pd(111) surfaces. II

Cited by 308 publications

References 18 publications

Electrochemical promotion of CH4 oxidation on Pd

Electrochemical promotion of CH4 oxidation on Pd

Oxygen Overlayers on Pd(111) Studied by Density Functional Theory

Influence of Step Sites on Thermal Behavior of NO on Stepped Pd(112) Studied by AES, XPS and UPS

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