Spectroscopic Link between Adsorption Site Occupation and Local Surface Chemical Reactivity

Baraldi, Alessandro; Lizzit, Silvano; Comelli, Giovanni; Кискинова, М.; Rosei, R.; Honkala, Karoliina; Nørskov, Jens K.

doi:10.1103/physrevlett.93.046101

Cited by 38 publications

(38 citation statements)

References 24 publications

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“…Remarkable quantitative agreement concerning the energetics, geometries, and SCLS values of the investigated (1 × 1)-H, (2 × 2)-(O+H), and (2 × 2)-(O+3H) (co)adsorbate overlayers on Ru(0001) is achieved. The quasi-linear dependence of the adsorbate-induced SCLSs on the number of directly coordinated nearest neighbors reported before for O overlayers on Ru(0001) [4], Rh(111) [3] and Rh(100) [2], as well as for H adsorbate layers on all Rh low-index single crystal surfaces [5] is found to prevail also in the H-(co)adsorbate structures on Ru(0001). The computed decomposition of the total SCLSs into initial-and finalstate contributions reveals an enhanced screening at the surface of the (co)adsorbate layers that is of the same order of magnitude as for the pure O overlayers studied before.…”

Section: Discussionmentioning

confidence: 79%

“…A quantitative understanding of the corresponding shifts, in particular of surface atoms coordinated to atomic or molecular adsorbates, provides a wealth of information e.g. on the nature of the chemical bond [1] and may even be used for the interpretation and prediction of surface reactions [2]. Experimentally, the shifts can be accessed by high-resolution X-ray photoelectron spectroscopy (XPS), as part of the so-called surface core level shifts (SCLSs) [1].…”

Section: Introductionmentioning

confidence: 99%

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O- and H-induced surface core level shifts on Ru(0001): prevalence of the additivity rule

Lizzit

Zhang

Kostov

et al. 2009

J. Phys.: Condens. Matter

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In previous work on adsorbate-induced surface core level shifts (SCLSs), the effects caused by O atom adsorption on Rh(111) and Ru(0001) were found to be additive: the measured shifts for first layer Ru atoms depended linearly on the number of directly coordinated O atoms. Densityfunctional theory calculations quantitatively reproduced this effect, allowed separation of initial and final state contributions, and provided an explanation in terms of a roughly constant charge transfer per O atom. We have now conducted similar measurements and calculations for three well-defined adsorbate and coadsorbate layers containing O and H atoms: (1 × 1)-H, (2 × 2)-(O+H), and (2 × 2)-(O+3H) on Ru(0001). As H is stabilized in fcc sites in the prior two structures and in hcp sites in the latter, this enables us to not only study coverage and coadsorption effects on the adsorbate-induced SCLSs, but also the sensitivity to similar adsorption sites. Remarkably good agreement is obtained between experiment and calculations for the energies and geometries of the layers, as well as for all aspects of the SCLS values. The additivity of the next-neighbor adsorbate-induced SCLSs is found to prevail even for the coadsorbate structures. While this confirms the suggested use of SCLSs as fingerprints of the adsorbate configuration, their sensitivity is further demonstrated by the slightly different shifts unambiguously determined for H adsorption in either fcc or hcp hollow sites.

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Section: Discussionmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

O- and H-induced surface core level shifts on Ru(0001): prevalence of the additivity rule

Lizzit

Zhang

Kostov

et al. 2009

J. Phys.: Condens. Matter

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“…Oxygen contamination, both in terms of chemisorbed atoms or oxidic species, has the effect of increasing the Rh 3d 5/2 BE on Rh atoms. 41,42 Other contamination sources have been thoroughly excluded via careful quantitative XPS.By increasing the annealing temperature, we observe a progressive decrease of the overall photoemission signal, as evidenced in Figure 3c,d. This behavior, due to inelastic mean free path effects in 3D structures, is in agreement with the STM-observed cluster morphological evolution since we can unambiguously exclude both Rh evaporation and intercalation.…”

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confidence: 76%

Section: Resultsmentioning

confidence: 99%

Local Electronic Structure and Density of Edge and Facet Atoms at Rh Nanoclusters Self-Assembled on a Graphene Template

et al. 2012

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T he interest in developing novel materials using building blocks with sizes of about 1 nm has motivated the huge effort devoted to understand the properties of nanoclusters. Several studies have clearly demonstrated that atomic aggregates in the nanometer size range, that is, formed by dozens or hundreds of atoms, present remarkably different properties with respect to their bulk crystalline counterparts. Heterogeneous catalysis, energy conversion, and magnetic data storage are among the technologically most relevant fields where supported nanoclusters are expected to have a strong impact. 1,2 An important field for application of the new nanocluster-based materials is catalysis. The most striking example is the high chemical activity of small Au nanoclusters, 3À6 given by highly reactive corner and edge atoms with low coordination number C N , but even other transition metals like Pt present nanoclusters with a similar behavior. 7,8 One of the goals of nanotechnology is the manipulation of the magnetic properties in systems with reduced dimensionality, such as quantum wires, quantum dots, and nanoclusters. As an example, the use of nanoclusters for ultrahigh density magnetic recording requires pushing further away the superparamagnetic limit by enhancing the magnetic anisotropy energy. In this respect, experiments have shown that low C N atoms play a pivotal role. 9,10 When the particle's size is reduced to only 10À20 Å, two main challenges are posed: (i) the formation in a controllable and reproducible manner of large-scale replicas of these individual building blocks on a suitable substrate 11 and (ii) the determination and tuning of the geometric and electronic structure of the supported nanoobjects.One of the most recent solutions to meet the first challenge is to make use of template graphene (GR) for the growth of metallic nanoclusters and for the formation of long-range-ordered superstructures. This * Address correspondence to alessandro.baraldi@elettra.trieste.it.Received for review November 24, 2011 and accepted March 9, 2012. Published online 10.1021/nn300651s ABSTRACTThe chemical and physical properties of nanoclusters largely depend on their sizes and shapes. This is partly due to finite size effects influencing the local electronic structure of the nanocluster atoms which are located on the nanofacets and on their edges. Here we present a thorough study on graphene-supported Rh nanocluster assemblies and their geometrydependent electronic structure obtained by combining high-energy resolution core level photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory. We demonstrate the possibility to finely control the morphology and the degree of structural order of Rh clusters grown in register with the template surface of graphene/Ir(111). By comparing measured and calculated core electron binding energies, we identify edge, facet, and bulk atoms of the nanoclusters. We describe how small interatomic distance changes occur while varying the nanocluster size, substantia...

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“…model, step-metal atoms should thus be capable of binding adsorbates more strongly than the surface-metal atoms, which is indeed the result. The upshift in the d-band DOS causes an upshift of the whole electrostatic potential which can be measured by core-level spectroscopy [53,54].…”

Section: Surface Stepsmentioning

confidence: 99%

Special Sites at Noble and Late Transition Metal Catalysts

2006

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An overview of recent advancements in density functional theory modeling of particularly reactive sites at noble and late transition metal surfaces is given. Such special sites include sites at the flat surfaces of thin metal films, sites at stepped surfaces, sites at the metal/oxide interface boundary for oxide-supported metal clusters, and sites at the perimeter of oxide islands grown on metal surfaces. The Newns-Anderson model of the electronic interaction underlying chemisorption is described. This provides the grounds for introducing the Hammer-Nørskov d-band model that correlates changes in the energy center of the valence d-band density of states at the surface sites with their ability to form chemisorption bonds. A reactivity change described by this model is characterized as an electronic structure effect. Brønsted plots of energy barriers versus reaction energies are discussed from the surface reaction perspective and are used to analyze the trends in the calculated changes. Deviations in the relation between energy barriers and reaction energies in Brønsted plots are identified as due to atomic structure effects. The reactivity change from pure Pd surfaces to Pd thin films supported on MgO can be assigned to an electronic effect. Likewise for the reactivity change from flat Au surfaces, over Au thin films to Au edges and the Au/MgO interface boundary. The reactivity enhancement at atomic step sites is of both electronic and atomic structure nature for NO dissociation at Ru, Rh and Pd surfaces. The enhancement of the CO oxidation reactivity when moving from a CO+O coadsorption structure on Pt(111) to the PtO 2 oxide island edges supported by Pt (111) is, however, identified as mainly an atomic structure effect. As such, it is linked to the occurrence of favorable pathways at the oxide island edges and is occurring despite of stronger adsorbate binding of the oxygen within the oxide edge, i.e. despite of an opposing electronic effect. As a final topic, a discussion is given of the accuracy of density functional theory in conjunction with surface reactions; adsorption, desorption, diffusion, and dissociation. Energy barriers are concluded to be more robust with respect to changes in the exchange-correlation functional than are molecular bond and adsorption energies.Theoretical modeling of heterogeneous catalysis can be approached in a number of ways with focus on different physico-chemical processes. The most fundamental process is the bond-breaking and bond-making of the individual molecules at the surface. However, topics such as the physical appearance of the solid surface (e.g. its degree of oxidation or corrugation), the interaction at the surface of reactants, reaction intermediates, and products (e.g. the degree to which they form ordered surface structures), and the flow of reactants towards the surface and of products away from the surface are other important fundamental processes. In the present review, the emphasis will be on the quantum mechanical modeling of the reaction energy profiles for s...

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Spectroscopic Link between Adsorption Site Occupation and Local Surface Chemical Reactivity

Cited by 38 publications

References 24 publications

O- and H-induced surface core level shifts on Ru(0001): prevalence of the additivity rule

O- and H-induced surface core level shifts on Ru(0001): prevalence of the additivity rule

Local Electronic Structure and Density of Edge and Facet Atoms at Rh Nanoclusters Self-Assembled on a Graphene Template

Special Sites at Noble and Late Transition Metal Catalysts

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