Transition from Molecule to Solid State: Reactivity of Supported Metal Clusters

Sitja, Georges; Moal, Séverine Le; Marsault, M.; Hamm, G.; Leroy, F.; Henry, Claude R.

doi:10.1021/nl304741t

Cited by 50 publications

(102 citation statements)

References 54 publications

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“…For largest particle size (3.5 nm=∼3848 atoms), the adsorption energy is of the order of 31.07 kcal mol -1 . This value is very close to the bulk Pd expected value (33.03 kcal mol -1 ) [18]. In an experimental study it is reported that the CO oxidation depends on the particle size, where Pd n (n≤6) are more reactive than larger clusters [20].…”

Section: Introductionsupporting

confidence: 85%

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The CO oxidation mechanism on small Pd clusters. A theoretical study

et al. 2015

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CO is a pollutant that is removed by oxidation using Pd, Pt or Rh as catalysts in the exhaust pipes of vehicles. Here, a quantum chemistry study on the CO + O2 reaction catalyzed by small Pdn clusters (n ≤ 5) using the PBE/TZ2P/ZORA method is performed. The limiting step in this reaction at low temperature and coverage is the O2 dissociation. Pdn clusters catalyze the O=O bond breaking, reducing the energy barrier from 119 kcal mol(-1) without catalyst to ∼35 kcal mol(-1). The charge transfer from Pd to the O2,ad antibonding orbital weakens, and finally breaks the O─O bond. The CO oxidation takes place by the Eley-Rideal (ER) mechanism or the Langmuir-Hinshelwood (LH) mechanism. The ER mechanism presents an energy barrier of 4.10-7.05 kcal mol(-1) and the formed CO2 is released after the reaction. The LH mechanism also shows barrier energies to produce CO2 (7-15 kcal mol(-1)) but it remains adsorbed on Pd clusters. An additional energy (7-25 kcal mol(-1)) is necessary to desorb CO2 and release the metal site. The triplet multiplicity is the ground states of studied Pdn clusters, with the following order of stability: triplet > singlet > quintet state. Graphical Abstract CO oxidation mechanism on small Pd clusters.

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Section: Introductionsupporting

confidence: 85%

“…For instance, the CO adsorption energy depends on the Pd cluster size [18,19]. For 4.7±2 atoms clusters, the CO adsorption energy is 21.08 kcal mol -1 and the CO chemisorption presents strongly irregular variation up to 1.8 nm (∼142 atoms) with energies of 5.98 kcal mol -1 .…”

Section: Introductionmentioning

confidence: 99%

The CO oxidation mechanism on small Pd clusters. A theoretical study

et al. 2015

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“…In many fundamental research fields, notably in surface science [1], they serve as model templates and atomically controlled spacers, for the manipulation and study of nanoparticles [2][3][4], molecules [5][6][7][8][9][10], or single atoms [11]. Most of the time, chemical stability of insulating thin films upon charged particle irradiation is required, e.g., for characterization using electron spectroscopy and microscopy.…”

Section: Introductionmentioning

confidence: 99%

Reaction kinetics of ultrathin NaCl films on Ag(001) upon electron irradiation

et al. 2017

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We report on an electron-induced modification of alkali halides in the ultrathin film regime. The reaction kinetics and products of the modifications are investigated in the case of NaCl films grown on Ag(001). Their structural and chemical modification upon irradiation with electrons of energy 52-60 eV and 3 keV is studied using low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES), respectively. The irradiation effects on the film geometry and thickness (ranging from between two and five atomic layers) are examined using scanning tunneling microscopy (STM). We observe that Cl depletion follows different reaction kinetics, as compared to previous studies on NaCl thick films and bulk crystals. Na atoms produced from NaCl dissociation diffuse to bare areas of the Ag(001) surface, where they form Na-Ag superstructures that are known for the Na/Ag(001) system. The modification of the film is shown to proceed through two processes, which are interpreted as a fast disordering of the film with removal of NaCl from the island edges and a slow decrease of the structural order in the NaCl with formation of holes due to Cl depletion. The kinetics of the Na-Ag superstructure growth is explained by the limited diffusion on the irradiated surface, due to aggregation of disordered NaCl molecules at the substrate step edges.

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“…The estimated number of exposed Pd atoms was calculated by using a simple hemisphere model for the cluster shape, a shape identified experimentally for similar-sized Pd clusters in a CO-containing atmosphere. [55] In brief, the surface atoms form a hemispherical shell of thickness of one Pd atom (d ¼ 0.27 nm). The shell outer radius is the cluster radius (R), assuming the bulk Pd density (considering this to be the reality), and its inner radius is (R À d).…”

Section: Resultsmentioning

confidence: 99%

Catalytic oxidation of cyclohexane by size-selected palladium clusters pinned on graphite

Habibpour

Yin

Kwon

et al. 2013

Journal of Experimental Nanoscience

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We report the catalytic oxidation of cyclohexane to CO and CO 2 over size-selected palladium clusters (Pd N clusters, N ¼ 10-120) supported on graphite as a function of cluster size. The stability of the pinned clusters (nanoparticles) under reaction conditions is investigated by scanning tunnelling microscopy measurement both before and after reaction. Temperature-programmed reaction experiments at 800 Torr show that the turnover rates (per surface Pd atom) for both CO and CO 2 increase significantly as cluster size decreases and correlate with the number of Pd perimeter atoms at the graphite interface. Under oxygenrich conditions, the activity of the clusters increases by a factor of 3 while the product ratio CO:CO 2 rises by an order of magnitude.

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Transition from Molecule to Solid State: Reactivity of Supported Metal Clusters

Cited by 50 publications

References 54 publications

The CO oxidation mechanism on small Pd clusters. A theoretical study

The CO oxidation mechanism on small Pd clusters. A theoretical study

Reaction kinetics of ultrathin NaCl films on Ag(001) upon electron irradiation

Catalytic oxidation of cyclohexane by size-selected palladium clusters pinned on graphite

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