Formation of a metastable ordered surface phase due to competitive diffusion and adsorption kinetics: Oxygen on Pd(100)

Chang, Shinn‐Liang; Thiel, Patricia A.

doi:10.1103/physrevlett.59.296

Cited by 79 publications

(44 citation statements)

References 11 publications

(10 reference statements)

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“…For this purpose we concentrate on a simple model case, namely the on-surface ordering of atomic adsorbates at a (100) cubic surface, for which extensive studies with model interactions have already been performed. 6,7,8,9,10,11,12,13 To make contact with a specific material and with experiment, we specifically choose the on-surface adsorption of oxygen at Pd(100), for which detailed experimental data on the ordering behavior is available 14 . Since in this system higher oxygen coverages above Θ ∼ 0.5 monolayers [ML, defined with respect to the number of Pd atoms in one layer of Pd(100)] induce structures containing incorporated oxygen 14,15,16,17,18 , we concentrate on the low coverage regime.…”

Section: 345mentioning

confidence: 99%

Accuracy of first-principles lateral interactions: Oxygen at Pd(100)

2007

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We employ a first-principles lattice-gas Hamiltonian (LGH) approach to determine the lateral interactions between O atoms adsorbed on the Pd(100) surface. With these interactions we obtain an ordering behavior at low coverage that is in quantitative agreement with experimental data. Uncertainties in the approach arise from the finite LGH expansion and from the approximate exchange-correlation (xc) functional underlying the employed density-functional theory energetics. We carefully scrutinize these uncertainties and conclude that they primarily affect the on-site energy, which rationalizes the agreement with the experimental critical temperatures for the order-disorder transition. We also investigate the validity of the frequently applied assumption that the ordering energies can be represented by a sum of pair terms. Restricting our LGH expansion to just pairwise lateral interactions, we find that this results in effective interactions which contain spurious contributions that are of equal size, if not larger than any of the uncertainties e.g. due to the approximate xc functional.

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Section: 345mentioning

confidence: 99%

Accuracy of first-principles lateral interactions: Oxygen at Pd(100)

2007

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“…For sufficiently low T, limited O mobility will inhibit equilibration of the O adlayer, 26 and will not be possible to characterize these states in terms of a few macrovariables. However, since the typical reaction barrier for CO oxidation on Pd͑100͒ of ϳ1 eV is significantly above the low-coverage O͑ads͒ diffusion barrier of ϳ0.6 eV, one should expect O mobility to be significant under typical reaction conditions.…”

Section: Further Discussion and Conclusionmentioning

confidence: 99%

“…The following dynamical processes are included in our reaction model: nonactivated adsorption of CO͑gas͒ on single empty sites of any type at rate P CO ͑in unit of ML/s͒; nonactivated dissociative adsorption of O 2 ͑gas͒ on diagonally adjacent empty 4fh sites, provided that the six adjacent neighbors are free of O͑ads͒ ͑the eight-site rule 10,14,19,25,26 ͒ at rate P O 2 ͑ML/s͒; activated desorption of CO with barrier determined by the total adsorption energy ͑desorption of oxygen is effectively inoperative under typical reaction conditions͒; reaction to form CO 2 ͑gas͒ of CO͑ads͒-O͑ads͒ pairs with a barrier of 0.73 eV ͑0.95 eV͒ for pairs separated by a ͑by ͱ 5a / 2 and ͱ 2a͒, where these barriers are based on DFT analysis 27 and comparison with experimental temperatureprogramed-reaction ͑TPR͒ spectra; 28 and diffusive hopping of both CO͑ads͒ and O͑ads͒ as described below.…”

Section: Lattice-gas Model For Co Oxidation On Pd"100…mentioning

confidence: 99%

Chemical diffusion of CO in mixed CO+O adlayers and reaction-front propagation in CO oxidation on Pd(100)

Liu

Evans

2006

The Journal of Chemical Physics

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Within the framework of a realistic atomistic lattice-gas model, we present the theoretical formulation and simulation procedures for precise analysis of the chemical diffusion flux of highly mobile CO within a nonuniform interacting mixed CO+O adlayer on a Pd(100) surface. The approach applies in both regimes of relatively immobile unequilibrated and fairly mobile near-equilibrated O adlayer distributions. Spatiotemporal behavior in surface reactions is controlled by chemical diffusion in mixed adlayers. Thus, we naturally integrate the above analysis with a previously developed multiscale modeling strategy to describe mesoscale reaction front propagation in CO oxidation on Pd(100). This treatment avoids using a simplified prescription of chemical diffusion and reaction kinetics as in traditional mean-field reaction-diffusion equation approaches. KeywordsAtomistic lattice-gas model, chemical diffusion flux, reaction-diffusion equation, reaction-front propagation, computer simulation, diffusion in gases, oxidation, palladum, reaction kinetics, surface reactions, carbon monoxide Within the framework of a realistic atomistic lattice-gas model, we present the theoretical formulation and simulation procedures for precise analysis of the chemical diffusion flux of highly mobile CO within a nonuniform interacting mixed CO+O adlayer on a Pd͑100͒ surface. The approach applies in both regimes of relatively immobile unequilibrated and fairly mobile near-equilibrated O adlayer distributions. Spatiotemporal behavior in surface reactions is controlled by chemical diffusion in mixed adlayers. Thus, we naturally integrate the above analysis with a previously developed multiscale modeling strategy to describe mesoscale reaction front propagation in CO oxidation on Pd͑100͒. This treatment avoids using a simplified prescription of chemical diffusion and reaction kinetics as in traditional mean-field reaction-diffusion equation approaches.

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“…͑ii͒ Dissociative adsorption of O 2 ͑gas͒ onto second or diagonal NN empty sites, provided that the additional six NN sites are not occupied by O͑ads͒ ͑the ''eight-site rule''͒. 18,19 Also O͑ads͒ can hop to NN empty sites provided that no adjacent pairs of O͑ads͒ are thus created. ͑iii͒ Reaction of adjacent CO͑ads͒ and O͑ads͒ to form CO 2 ͑gas͒.…”

Section: Co-oxidation Modelsmentioning

confidence: 99%

Surface diffusion in mixed overlayers with superlattice ordering: Percolative transport around obstacles and along domain boundaries

Liu¹,

Evans²

2000

The Journal of Chemical Physics

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To elucidate surface diffusion in the presence of a coadsorbate with superlattice ordering, we consider particle hopping on a square lattice with some fraction, u B , of quenched blocking sites arranged with checkerboard or c(232) ordering. Behavior for low u B corresponds to diffusion around isolated obstacles, and can be described by exact density expansions. Behavior for high u B corresponds to percolative diffusion along ~or sometimes away from! domain boundaries. The connectivity of these domain boundaries is closely related to the existence of symmetry breaking @i.e., long-range c(232) order# in the distribution of blocking sites. In some cases, symmetry breaking induces critical behavior for diffusive transport which is fundamentally different from that for the conventional ''ant in the labyrinth'' problem. Our results apply to recently developed models for CO oxidation, where CO~ads! diffuses rapidly through coadsorbed relatively immobile c(2 32)-O~ads!. The characterization of CO diffusion in these systems is key to describing spatial pattern formation. Disciplines Biological and Chemical Physics | Mathematics CommentsThe following article appeared in Journal of Chemical Physics 113, 22 (2000) To elucidate surface diffusion in the presence of a coadsorbate with superlattice ordering, we consider particle hopping on a square lattice with some fraction, B , of quenched blocking sites arranged with checkerboard or c(2ϫ2) ordering. Behavior for low B corresponds to diffusion around isolated obstacles, and can be described by exact density expansions. Behavior for high B corresponds to percolative diffusion along ͑or sometimes away from͒ domain boundaries. The connectivity of these domain boundaries is closely related to the existence of symmetry breaking ͓i.e., long-range c(2ϫ2) order͔ in the distribution of blocking sites. In some cases, symmetry breaking induces critical behavior for diffusive transport which is fundamentally different from that for the conventional ''ant in the labyrinth'' problem. Our results apply to recently developed models for CO oxidation, where CO͑ads͒ diffuses rapidly through coadsorbed relatively immobile c(2 ϫ2)-O͑ads͒. The characterization of CO diffusion in these systems is key to describing spatial pattern formation.

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Formation of a metastable ordered surface phase due to competitive diffusion and adsorption kinetics: Oxygen on Pd(100)

Abstract: A metastable c(2x2) structure is formed by atomic oxygen on Pd(100) under conditions of slow diffusion combined with rapid adsorption.We propose that formation of the c(2x2) under these conditions must be controlled by characteristics of the dissociative adsorption event itself.

Cited by 79 publications

References 11 publications

Accuracy of first-principles lateral interactions: Oxygen at Pd(100)

Accuracy of first-principles lateral interactions: Oxygen at Pd(100)

Chemical diffusion of CO in mixed CO+O adlayers and reaction-front propagation in CO oxidation on Pd(100)

Surface diffusion in mixed overlayers with superlattice ordering: Percolative transport around obstacles and along domain boundaries

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