Adsorption and energetics of isolated CO molecules on Pd(111)

Sautet, Philippe; Rose, M.; Dunphy, J.C.; Behler, S.; Salmerón, Miquel

doi:10.1016/s0039-6028(00)00243-0

Cited by 68 publications

(54 citation statements)

References 20 publications

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“…The results can be correlated with the behavior of other systems at high coverage, where only the NO or CO molecules on top positions adsorbed on metallic surfaces were observed. [1][2][3]5,6,12,15,44 For the p͑2 ϫ 2͒-3NO structure we can observe bright regular maxima with some shadows in between. The STM image is qualitatively similar to that obtained for p͑2 ϫ 2͒-NO on top ͑Fig.…”

Section: Stm Topographic Imagesmentioning

confidence: 99%

“…1 Theoretical calculations of the STM images therefore become necessary for a correct understanding of the experimental data. [2][3][4][5][6] Coupling experimental studies with theoretical approach makes it possible to obtain valuable information about the adsorption sites, bond lengths, and defects, and to determine which electronic states predominantly contribute to the observed STM pattern. Despite their strong relevance with the high pressure situation in heterogeneous catalysis, high coverage STM images have been studied less than low coverage ones.…”

Section: Introductionmentioning

confidence: 99%

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NO structures adsorbed on Rh(111): Theoretical approach to high-coverage STM images

et al. 2006

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Theoretical modeling of scanning tunneling microscopy ͑STM͒ measurements is used for the interpretation of images of nitrogen monoxide on Rh͑111͒ surfaces in order to gain insight into the factors which control the contrast of an STM image, especially in the case of high coverage overlayers. Topographic images of NO/Rh͑111͒ for different coverages and adsorption positions were calculated. These results were used to analyze the experimental images obtained for the p͑2 ϫ 2͒-3NO and p͑3 ϫ 3͒-7NO high coverage structures. The theoretical calculations confirm that not all NO molecules present on the surface can be observed experimentally, the image being dominated by the contribution of top NO molecules in the adlayer. In addition, the calculations reveal that destructive interference effects between molecular contributions in the tunnel current play a decisive role for the different contrast of the two high coverage structures. A general discussion of why and how the differences in the adsorbate surface configuration reflect the experimental STM images is given.

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Section: Stm Topographic Imagesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

NO structures adsorbed on Rh(111): Theoretical approach to high-coverage STM images

et al. 2006

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“…In the case of CO on Pd͑111͒, the bridge and threefold site are almost equal in energy. 51,52 Earlier studies proposed that the c͑4 ϫ 2͒ structure was formed by threefold-bound CO only. 52,53 However, more recent STM studies ͑partially by the same authors͒ indicate that in fact two types of c͑4 ϫ 2͒ islands coexist, one with bridge-bound CO, the other one with threefold-bound CO. 54 Other high-pressure vibrational spectroscopy studies also indicate that CO on Pd͑111͒ may be bound both to the top and the bridge site.…”

Section: B Adsorption On the Fcc(111) Surfacementioning

confidence: 99%

Bridge-bonded adsorbates on fcc(100) and fcc(111) surfaces: A kinetic Monte Carlo study

et al. 2006

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The adsorption of a bridge-bonded molecule onto fcc͑100͒ and fcc͑111͒ surfaces is studied using kinetic Monte Carlo simulations. The results are related to examples from both the electrochemical and the ultrahigh vacuum field. The lateral interaction model for the fcc͑100͒ surface with the least excluded neighbor sites does not cause ordering in the adlayer at saturation coverage. This is due to the availability of two equivalent bridge sites per surface atom. The model with the most excluded sites on the other hand causes the formation of a c͑4 ϫ 2͒ ordered structure with a coverage of 0.25 ML. Surprisingly, for the model with intermediate-ranged lateral interactions a one-dimensionally ordered structure is found. In this one-dimensionally ordered structure, bridge-bonded anions are aligned along the ͱ 2 direction. The spacing between these rows varies, since each new row can form at either one of the two kinds of bridge site per surface atom. The local distribution between these one-dimensional rows can be described by, respectively, a c͑2 ͱ 2 ϫ ͱ 2͒ or a ͑ ͱ 2 ϫ ͱ 2͒ unit cell ͓the latter one is also referred to as c͑2 ϫ 2͔͒. On the fcc͑111͒ surface, once again no ordered structure is found for the model with the smallest number of excluded sites. For the models with more excluded sites a c͑4 ϫ 2͒ ordered structure ͓also known as c͑2 ϫ ͱ 3͔͒ and a ͑ ͱ 3 ϫ ͱ 7͒ ordered structure are formed, the coverages being 0.50 and 0.20 ML, respectively. The simulated voltammograms generally show a broad peak due to adsorption in a disordered phase, and, if a two-dimensionally ordered structure is formed, a second sharp peak due to a disorder-order transition in the adlayer. The formation of the one-dimensionally ordered structure does not cause an additional current peak in the voltammogram.

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“…Low energy electron diffraction (LEED) [36,37] and x-ray photoelectron diffraction (XPD) [38] studies have shown that at high coverage (0.75 ML) NO forms a (2 × 2)-3NO structure analogous to the one formed by CO. An important characteristic of the STM images of the dense (2 × 2) structures is that only top-site molecules produce a high contrast, while those bound to hollow sites have electronic structures and orbital symmetries that makes their contribution to the tunneling current much smaller than those on top-sites. Thus these molecules are not imaged [39].…”

Section: Mixed (2×2)-3(co-no) Structurementioning

confidence: 99%

Adsorbate structures and catalytic reactions studied in the torrpressure range by scanning tunneling microscopy

Hwang

2003

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STM studies of NO on Rh(111) showed that adsorbed NO forms two highpressure structures, with the phase transformation from the (2 × 2) structure to the (3 × 3) structure occurring at 0.03 Torr. The (3 × 3) structure only exists when the surface is in equilibrium with the gas phase. The heat of adsorption of this new structure was determined by measuring the pressures and temperatures at which both (2 × 2) and (3 × 1 3) structures coexisted. The energy barrier between the two structures was calculated by observing the time necessary for the phase transformation to take place.High-pressure STM studies of the coadsorption of CO and NO on Rh (111) showed that CO and NO form a mixed (2 × 2) structure at low NO partial pressures. By comparing surface and gas compositions, the adsorption energy difference between topsite CO and NO was calculated. Occasionally there is exchange between top-site CO and NO, for which we have described a mechanism for. At high NO partial pressures, NO segregates into islands, where the phase transformation to the (3 × 3) structure occurs.The reaction of CO and NO on Rh(111) was monitored by mass spectrometry (MS) and HPHTSTM. From MS studies the apparent activation energy of the catalytic converter reaction was calculated and compared to theory. STM showed that under hightemperature reaction conditions, surface metal atoms become mobile.Ethylene hydrogenation and its poisoning by CO was also studied by STM on Rh(111) and Pt(111). Poisoning was found to coincide with decreased adsorbate mobility. Under ethylene hydrogenation conditions, no order is detected by STM at 300 K, as hydrogen and ethylidyne, the surface species formed by gas-phase ethylene, are too mobile. When CO is introduced, the reaction stops, and ordered structures appear on the surface. For Rh(111), the structure is predominantly a mixed c(4 × 2), though there are some areas of (2 × 2). For Pt(111), the structure is hexagonal and resembles the Moiré pattern seen when Pt(111) is exposed to pure CO. From these studies it is concluded that CO poisons by stopping adsorbate mobility. This lack of adsorbate mobility prevents the adsorption of ethylene from the gas phase by hindering the creation of adsorption sites. 2Dedicated to my parents, Warren and Cordelia Hwang.

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Adsorption and energetics of isolated CO molecules on Pd(111)

Cited by 68 publications

References 20 publications

NO structures adsorbed on Rh(111): Theoretical approach to high-coverage STM images

NO structures adsorbed on Rh(111): Theoretical approach to high-coverage STM images

Bridge-bonded adsorbates on fcc(100) and fcc(111) surfaces: A kinetic Monte Carlo study

Adsorbate structures and catalytic reactions studied in the torrpressure range by scanning tunneling microscopy

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