Adsorption kinetics and isotopic equilibration of oxygen adsorbed on the Pd(111) surface

Guo, Xuan; Hoffman, A.; Yates, John T.

doi:10.1063/1.456386

Cited by 173 publications

(112 citation statements)

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“…He also observed repulsive interactions between the oxygen species as the oxygen coverage was increased. The repulsive interactions between the surface oxygen species have been also reported by Guo et al [6] using Pd (111) at adsorption temperature -173°C. Weissman et al [7] refers to the existence of two states of oxygen, on Pd (111), at room temperature, one on the surface (T p = 560°C) and one beneath it (T p = 870°C).…”

Section: Oxygen Adsorption On Pd Surfacesmentioning

confidence: 52%

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Temperature programmed desorption of oxygen from Pd films interfaced with Y2O3-doped ZrO2

Katsaounis

2008

J Appl Electrochem

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The origin of the effect of non-faradaic electrochemical modification of catalytic activity (NEMCA) or Electrochemical Promotion was investigated via temperature-programmed-desorption (TPD) of oxygen, from polycrystalline Pd films deposited on 8 mol%Y 2 O 3 -stabilized-ZrO 2 (YSZ), an O 2-conductor, under high-vacuum conditions and temperatures between 50 and 250°C. Oxygen was adsorbed both via the gas phase and electrochemically, as O 2-, via electrical current application between the Pd catalyst film and a Au counter electrode. Gaseous oxygen adsorption gives two adsorbed atomic oxygen species desorbing at about 300°C (state b 1 ) and 340-500°C (state b 2 ). The creation of the low temperature peak is favored at high exposure times (exposure [1 kL) and low adsorption temperatures (T ads \ 200°C). The decrease of the open circuit potential (or catalyst work function) during the adsorption at high exposure times, indicates the formation of subsurface oxygen species which desorbs at higher temperatures (above 450°C). The desorption peak of this subsurface oxygen is not clear due to the wide peaks of the TPD spectra. The TPD spectra after electrochemical O 2-pumping to the Pd catalyst film show two peaks (at 350 and 430°C) corresponding to spillover O ads and O dÀ ads according to the reaction:The formation of the spillover O dÀ ads oxygen species is an intermediate stage before the formation of the atomic adsorbed oxygen, O ads . Mixed gaseous and electrochemical adsorption was carried out in order to simulate the Electrochemical Promotion conditions. The initial surface coverage with oxygen from the gas phase plays a very important role on the high or low effect of polarization. In general mixed adsorption leads to much higher oxygen coverages compare with that observed either under gaseous or electrochemical adsorption. The binding strength of the atomic adsorbed oxygen (state b 2 ) was investigated as a function of applied potential. It was found that the binding energy decreases linearly with increasing catalyst potential and work function. Similar behavior has been observed for oxygen adsorption on Pt, Ag and Au deposited on YSZ in previous studies.Keywords Temperature programmed desorption Á Oxygen adsorption on Pd Á Electrochemical promotion Á Electrochemical adsorption Á Palladium supported catalyst Á Spillover-backspillover of oxygen Á NEMCA effect 1 Introduction

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Section: Oxygen Adsorption On Pd Surfacesmentioning

confidence: 52%

“…(i) On single crystals Pd (111) [1][2][3][4][5][6][7][8][9][10] oxygen desorbs in a single wide peak between 500 and 580°C. Repulsive interactions are grown between the oxygen adsorbed species.…”

Section: Oxygen Adsorption On Pd Surfacesmentioning

confidence: 99%

Temperature programmed desorption of oxygen from Pd films interfaced with Y2O3-doped ZrO2

Katsaounis

2008

J Appl Electrochem

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“…The interaction of oxygen with Pd surfaces has been controversially discussed in the literature for more than thirty years (see e.g. [76][77][78][79][80][81][82][83] ).…”

Section: Kinetic Experiments On Complex Model Catalystsmentioning

confidence: 99%

Model studies in heterogeneous catalysis at the microscopic level: from the structure and composition of surfaces to reaction kinetics

et al. 2006

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Heterogeneous catalysis is one of the fields of modern technology, in which a characterization of structural and chemical properties of solid surfaces at the microscopic level is of enormous importance. For a long time, such insights have been precluded by the complexity of most catalytically active materials. Recently, substantial progress has been made, however, toward a microscopic-level understanding of complex catalyst surfaces. We discuss the driving factors for these advancements, which are based on the development of new well-defined model systems as well as on advances in experimental technology and theory. Scrutinizing the example of planar model catalysts, we identify the process of linking structural and chemical information to microscopic reaction kinetics as a particular challenging aspect of today's work. We review the kinetic effects which may have an influence on the reaction kinetics on complex surfaces. As an example how structural and kinetic information can be correlated at the microscopic level we discuss the case of surface oxidation and oxygen induced restructuring of Pd nanoparticles as studied by molecular beam methods.

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“…The scattering geometry was set at 45°incidence and 45°exit. The surfaces were sputter cleaned and continuously dosed with O 2 , known to dissociate spontaneously on Pt and Pd [20,21], thus replenishing abstracted O atoms and providing a stable steady-state coverage (O 2 pressure dependent). Fast molecular NO and O 2 products, exiting the surface as ions, were mass analyzed with a quadrupole mass spectrometer (Extrel QPS); their exit energy was measured with an electrostatic energy analyzer at a constant pass energy of 15 eV.…”

Section: Direct or Eley-rideal Reactions Between Energetic Nmentioning

confidence: 99%

Kinematics of Eley-Rideal Reactions at Hyperthermal Energies

Yao

Giapis

2016

Phys. Rev. Lett.

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Direct or Eley-Rideal reactions between energetic N þ and O þ projectiles and O atoms, adsorbed onto Pt and Pd surfaces, are studied experimentally at incidence energies between 20 and 200 eV. The exit energies of the diatomic molecular products NO and O 2 depend linearly on the incidence energy of the corresponding projectiles. A reaction mechanism is proposed, where the incident projectile collides with a single metal atom on the surface, linked to an adsorbed O atom. At the apsis point, a high-energy transient state is formed between the projectile, substrate, and adsorbate atoms. As the projectile begins to rebound, the transient state decomposes into a diatomic molecule, consisting of the original projectile and the adsorbed O atom, which exits the surface with memory of the incidence energy. Energy and momentum conservation during this single-bounce event (atom in, molecule out) accurately predict the exit energy of the molecular product, thus capturing the kinematics of the direct reaction. DOI: 10.1103/PhysRevLett.116.253202 Gas-surface reactions are often thought to proceed between two extremes: the Langmuir-Hinshelwood (LH) mechanism, which requires all reactants to be adsorbed onto and in thermal equilibrium with the surface, and the Eley-Rideal (ER) mechanism, where an energetic reactant (the "projectile") impinges onto a surface adsorbate and bonds with it directly [1]. The LH mechanism applies to most surface chemical reactions and is well understood [2]. The ER mechanism is still being debated: the rarity of chemical environments where hyperthermal reactive species bombard surfaces, combined with experimental difficulties in detecting energetic reaction products, has impeded progress in understanding such reactions. In fact, even the definition of an ER reaction is outright crude: the notion of a bond forming between an energetic projectile and a surface adsorbate in a head-on collision, followed up by ejection from the surface of an energetic reaction product, violates momentum conservation. This problem does not arise if the projectile collides first with the surface. Hot atom reactions represent an intermediate mechanism, where the projectile undergoes few bounces before reacting with an adsorbate [3]. Owing to multiple collisions, which lead to variable energy losses, these do not qualify as prompt ER reactions.What comprises an ER reaction? The literature consensus suggests that ER reactions should have at least the following attributes: (i) they require a gas-phase projectile with high kinetic or potential energy, impinging onto an adsorbate-covered surface; (ii) they yield a fast-moving molecular product, consisting of the projectile-adsorbate combination, which leaves the surface (no trapping); and (iii) the product translational energy must be directly correlated to the energy of the incident projectile. Secondary attributes include that (iv) the product molecule may be internally excited; and (v) the product angular flux distribution deviates from the cosine law, with subspecular pref...

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Adsorption kinetics and isotopic equilibration of oxygen adsorbed on the Pd(111) surface

Cited by 173 publications

References 24 publications

Temperature programmed desorption of oxygen from Pd films interfaced with Y2O3-doped ZrO2

Temperature programmed desorption of oxygen from Pd films interfaced with Y2O3-doped ZrO2

Model studies in heterogeneous catalysis at the microscopic level: from the structure and composition of surfaces to reaction kinetics

Kinematics of Eley-Rideal Reactions at Hyperthermal Energies

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