Atomic-resolution imaging of size-selected platinum clusters on TiO2(110) surfaces

Isomura, Noritake; Wu, Xingyang; Watanabe, Yoshihide

doi:10.1063/1.3251786

Cited by 47 publications

(59 citation statements)

References 25 publications

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“…36 Most of the Pt 7 clusters are also one atomic layer high; however, there is a clear tail toward double-layer height that is absent for Pt 3 . Pt 10 clusters have a symmetric histogram centered at double-layer height, with equal weights on single-and triple-layer apparent heights.…”

Section: ■ Resultsmentioning

confidence: 99%

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

et al. 2014

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We determined the CO oxidation rates for sizeselected Pt n (n ∈ {3,7,10}) clusters deposited onto TiO 2 (110). In addition, we investigated the cluster morphologies and their mean sizes before and after the reaction. While the clusters are fairly stable upon annealing in ultrahigh vacuum up to 600 K, increasing the temperature while adsorbing either one of the two reactants leads to ripening already from 430 K on. This coarsening is even more pronounced when both reactants are dosed simultaneously, i.e., running the CO oxidation reaction. Since the ripening depends on the size initially deposited, there is nevertheless a size effect; the catalytic activity decreases monotonically with increasing initial cluster size. ■ INTRODUCTIONIt is well established that small metal clusters have physical and chemical properties distinctively different from those of the bulk. While the properties change rather smoothly in the socalled scalable size regime, each additional atom can substantially change the properties of interest in the nonscalable size range. 1 Metal clusters of well-defined size, shape, and composition, supporting on metal oxide surfaces, provide model catalysts that offer a fundamental understanding of the processes taking place in real catalysts via structure−reactivity correlation at the molecular level. 2 This has been shown for the smallest clusters in numerous examples, three decades ago in the famous photographic experiment by Fayet et al., 3 and more recently in the work of Heiz et al. for metal clusters on MgO(100) 4−9 and of Anderson et al., 10,11 Watanabe et al.,12 and our group 13 for metal clusters on rutile TiO 2 (110). In all these examples, size-selected cluster deposition was employed in order to prepare monodispersed supported clusters which are difficult to obtain by conventional preparation methods. We note that experiments with a finite cluster size distribution also make it possible to study size effects in the scalable regime by varying the mean cluster size. 14 However, to firmly associate a catalytic property with a certain size, one has to probe the cluster morphology not only before but also after the reaction. This information is essentially lacking in most of the experiments cited above.It is fairly well accepted that metal catalysts deactivate, in particular under reaction conditions, as a consequence of morphological changes of the supported clusters, and that this change depends on the cluster size and cluster−support interaction. 2,15−24 This argument is even more important when the smallest entities, with only a handful of atoms, are under investigation. Accordingly, not only in model catalysts with well-defined initial conditions but also in real catalysts, this stability under the reaction conditions sets a clear limitation to the minimum cluster size that can be reasonably employed.Here we present a systematic study of the initial sizedependent reactivity and of the thermal as well as chemical stability of very small Pt clusters on rutile TiO 2 (110)-(1×1) in ...

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Section: ■ Resultsmentioning

confidence: 99%

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

et al. 2014

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“…From a STM observation [1,2] for this system, it has been confirmed that the cluster structure for the number of Pt atoms, n ≤ 7, consists of single atomic layer of Pt (two dimensional (2D) cluster), however, two atomic layers of Pt (three dimensional (3D) cluster) for n ≥ 8. When such size selected Pt clusters on the substrate was tentatively observed by RHEED, the intensity distribution like a Debye-Sherrer ring pattern was very weakly observed.…”

Section: Introductionmentioning

confidence: 66%

“…New technology which forms size selected nano clusters with several numbers of Pt atoms has been developed [1,2]. Simultaneously, structure evaluation of such nano clusters is also required.…”

Section: Introductionmentioning

confidence: 99%

RHEED Patterns Calculated for Pt Nano Clusters on TiO<sub>2</sub>(110) Substrate

Horio

Watanabe

Takakuwa

et al. 2015

e-J. Surf. Sci. Nanotech.

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Platinum nano clusters, which are attractive material for highly activated catalysis, are usually evaluated by scanning tunneling microscopy (STM). Here we challenge to evaluate the structure of Pt nano clusters by reflection high-energy electron diffraction (RHEED) for the first time. The nano cluster models are made of n = 7 and n = 15 Pt atoms, which are deposited on TiO2(110) substrate. The former has two dimensional (planer) and the latter three dimensional (two layer's) shapes. They are rotated around their [111] axes of Pt crystal, whose axes are also inclined from the substrate surface normal because of the atomically rough substrate surface. The RHEED patterns have been calculated by kinematic diffraction theory. From the calculated patterns for the two types of the clusters (n = 7 and 15), it is found that there is characteristic difference in the radial intensity distributions. The difference is attributed to existence or absence of the higher order reflections which arise from two layers of Pt(111).

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“…High-resolution UHV-STM images of size-selected Pt(n) (n=4,7-10,15) clusters deposited on TiO 2 (110)-(1x1) surfaces were obtained using a CNT tip (Fig. 15) [65]. Clusters ofstructures of the top layers.…”

Section: (A) Mechanical Attachment Methodsmentioning

confidence: 99%

Laser-Combined STM and Related Techniques for the Analysis of Nanoparticles/Clusters

Shigekawa¹,

Yoshida²,

Yoshimura³

et al. 2012

Smart Nanoparticles Technology

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Atomic-resolution imaging of size-selected platinum clusters on TiO2(110) surfaces

Cited by 47 publications

References 25 publications

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

RHEED Patterns Calculated for Pt Nano Clusters on TiO<sub>2</sub>(110) Substrate

Laser-Combined STM and Related Techniques for the Analysis of Nanoparticles/Clusters

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Atomic-resolution imaging of size-selected platinum clusters on TiO2(110) surfaces

Cited by 47 publications

References 25 publications

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Ptn/TiO2(110)-(1×1)

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Ptn/TiO2(110)-(1×1)

RHEED Patterns Calculated for Pt Nano Clusters on TiO<sub>2</sub>(110) Substrate

Laser-Combined STM and Related Techniques for the Analysis of Nanoparticles/Clusters

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Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)