Oxidation-Resistant Gold-55 Clusters

Boyen, Hans‐Gerd; Kästle, G.; Weigl, F.; Koslowski, B.; Dietrich, Ch.; Ziemann, P.; Spatz, Joachim P.; Riethmüller, S.; Hartmann, Christoph; Möller, Martin; Schmid, Günter; Garnier, M. G.; Oelhafen, P.

doi:10.1126/science.1076248

Cited by 499 publications

(351 citation statements)

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“…Formation of surface oxide has been previously reported for gold surfaces exposed to atomic oxygen or oxygen plasma. 22,62,63 For instance, Au(core)/ Au 2 O 3 (shell) structures with oxide shell thicknesses of about 0.7 nm were obtained when gold clusters were exposed to atomic oxygen. 62 In previous XAS studies performed on Au/ TiO 2 and Au/Al 2 O 3 catalysts, only Au particles smaller than about 3 nm were found reactive to air, leading to oxidation of about 10% of the Au atoms, whereas larger particles did not seemed to be oxidized.…”

Section: Theoretical Resultsmentioning

confidence: 99%

Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO₂ Catalyst under Oxidative and Reducing Atmospheres

et al. 2010

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Diffuse optical reflectance of Au/TiO 2 powder catalysts, prepared by the deposition-precipitation method, is measured in the UV-visible range in controlled atmosphere. An intense optical absorption observed around 550 nm is interpreted by the excitation of plasmon resonances in the 4 nm gold nanoparticles (NPs). The location, intensity, and width of the absorption can be reproduced theoretically by using a distribution of shapes of the NPs. The changes of the reflectance upon exposure of the Au/TiO 2 catalyst to different atmospheres (O 2 /He, H 2 /He, CO/He) are measured in real-time by use of a homemade differential diffuse reflectance (DDR) spectrometer. The derivative-like DDR spectrum shows that the exposure to oxygen leads to the adsorption of oxygen species at the surface of the Au NPs. By modeling the DDR spectrum, we analyze different possible processes that could occur during the oxygen exposure and we find that the main effect is a charge transfer from gold to the adsorbed oxygen species, combined with a slight flattening of the Au NPs. The exposure to CO gives a similar but much smaller effect than the one of oxygen. Finally, real-time optical measurements performed during the exposures to oxygen indicate that two different sets of particles are probably present in the catalyst, and react with different kinetics, slightly flat three-dimensional NPs and very flat almost two-dimensional NPs.

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Section: Theoretical Resultsmentioning

confidence: 99%

Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO₂ Catalyst under Oxidative and Reducing Atmospheres

et al. 2010

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“…We applied this mass standard to study gold nanoparticles prepared by thermal vapor deposition and by colloidal wet chemistry, and from which we deduced the shapes of these two types of nanoparticles as expected. DOI: 10.1103/PhysRevLett.101.246103 PACS numbers: 81.07.Àb, 61.46.Bc, 61.46.Df, 68.37.Ma Since the properties of nanoclusters and nanoparticles depend critically on their size [1,2], the measurement of their mass is crucial. For example, knowledge of the mass, i.e., the number of atoms in the clusters, when coupled with the measured projected area of the nanoparticles, would enable us to deduce the 3D shape of the nanoparticles.…”

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confidence: 99%

“…Since the properties of nanoclusters and nanoparticles depend critically on their size [1,2], the measurement of their mass is crucial. For example, knowledge of the mass, i.e., the number of atoms in the clusters, when coupled with the measured projected area of the nanoparticles, would enable us to deduce the 3D shape of the nanoparticles.…”

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confidence: 99%

Weighing Supported Nanoparticles: Size-Selected Clusters as Mass Standards in Nanometrology

Young

Chen

et al. 2008

Phys. Rev. Lett.

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We present a new approach to quantify the mass and 3D shape of nanoparticles on supports, using sizeselected nanoclusters as mass standards in scanning transmission electron microscope. Through quantitative image intensity analysis, we show that the integrated high angle annular dark field intensities of size-selected gold clusters soft-landed on graphite display a monotonic dependence on the cluster size as far as $6500 atoms. We applied this mass standard to study gold nanoparticles prepared by thermal vapor deposition and by colloidal wet chemistry, and from which we deduced the shapes of these two types of nanoparticles as expected. DOI: 10.1103/PhysRevLett.101.246103 PACS numbers: 81.07.Àb, 61.46.Bc, 61.46.Df, 68.37.Ma Since the properties of nanoclusters and nanoparticles depend critically on their size [1,2], the measurement of their mass is crucial. For example, knowledge of the mass, i.e., the number of atoms in the clusters, when coupled with the measured projected area of the nanoparticles, would enable us to deduce the 3D shape of the nanoparticles. This is of particular importance in areas such as environmental health [3] and catalysis [4,5], because it regulates the effective surface area of the (typically supported) particles. However, atom counting is a challenging task for nanoparticles on surfaces, in terms of accuracy, efficiency, and mass range. Here we show that soft-landed size-selected atomic clusters can be used as mass standards which enable surface mass spectrometry by scanning transmission electron microscopy (STEM). For Au clusters on carbon surfaces, we find that the measured relationship between mass and the high angle annular dark field (HAADF) intensity in STEM displays a monotonic dependence on cluster size as far as $6; 500 atoms. This extends the applicable mass range for STEM-based mass spectrometry by about 3 orders of magnitude [6,7]. The method is demonstrated by the 3D shape determination of colloidal, evaporated and size-selected Au nanoparticles.There are a number of ways that the masses of nanoparticles on surfaces can be measured. Cantilever-based techniques have recently been demonstrated for mass detection at the zeptogram level (10 À21 g) [8,9]. Electronmicroscopy-based techniques have a long history [6,7,[10][11][12][13][14][15][16][17][18]. In Zeitler and Bahr's early work of 1962, the mass of nanoparticles has been determined down to 10 À18 g using STEM with an accuracy of 10% [17]. The advantage of this approach is that the mass information obtained can be directly correlated to the structure and properties of the particle studied. The concept of atomic-level mass determination by STEM, as developed by Howie, is a quantitative application of the HAADF-STEM imaging method [18,19]. This requires an accurate knowledge of the electron scattering cross section ( ) as a function of the number of atoms (N) and the number of electrons in the focused electron beam. Ab initio calculation of high angle electron scattering cross section of nanoparticles is a challenging...

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“…These properties have been related to changes in the electronic properties, the presence of defect sites, and the existence of strain for metallic gold nanoparticles. [4][5][6][7][8] Unique catalytic properties have also been related to the presence of sites associated with the catalyst support, such as cationic gold species, and sites at gold-support interfaces. [9,10] Here we show that it is possible to study the catalytic properties of metallic gold, without interference from a catalyst support, by using nanotubes of gold in polycarbonate membranes.…”

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confidence: 99%

Gold‐Nanotube Membranes for the Oxidation of CO at Gas–Water Interfaces

et al. 2004

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An exciting discovery in the area of heterogeneous catalysis is the observation that nanoparticles of gold on high-surfacearea supports exhibit high activity for oxidation of CO with O 2 (CO + 1/2 O 2 !CO 2 ) at room temperature. [1,2] This discovery is of particular relevance for the production of fuel-cell-grade hydrogen, since carbon monoxide must be removed from hydrogen streams generated by catalytic reforming of hydrocarbons.[3] The origins for the unique catalytic properties of supported gold catalysts are still unresolved. These properties have been related to changes in the electronic properties, the presence of defect sites, and the existence of strain for metallic gold nanoparticles. [4][5][6][7][8] Unique catalytic properties have also been related to the presence of sites associated with the catalyst support, such as cationic gold species, and sites at gold-support interfaces. [9,10] Here we show that it is possible to study the catalytic properties of metallic gold, without interference from a catalyst support, by using nanotubes of gold in polycarbonate membranes. These nanotubes exhibit catalytic activity for the oxidation of carbon monoxide by O 2 at room temperature, and this activity is enhanced by liquid water, promoted by increasing the pH of the solution, and increased using H 2 O 2 as the oxidizing agent. The rate can also be increased by depositing KOH within these nanotubes. These rates are comparable with those found in heterogeneous catalysis studies with gold nanoparticles on oxide supports, which suggests that the high activity of these latter catalysts may be related to the promotional effect of hydroxyl groups.Gold nanotubes of uniform size were prepared via a template-synthesis method by electroless deposition of gold [11] within the pores of a 10-mm-thick, track-etched polycarbonate membrane containing 220-nm-diameter pores.[12] All surfaces of the template membrane were first sensitized with a Sn II salt, activated by formation of a metallic Ag layer, followed by electroless deposition of gold for a period of 2 h. The gold nanotubes were cleaned with a 25 % HNO 3 solution for 15 h.[13] Hydrophobic or hydrophilic selfassembled monolayers were formed on gold nanotubes by rinsing the samples in ethanol for 20 min, followed by immersion for 17 h in solutions of ethanol containing HS(CH 2 ) 15 CH 3 or HS(CH 2 ) 15 COOH, respectively. [14] Gold nanotubes embedded within the pores of the polycarbonate template membranes were exposed by reactive ion etching (RIE) using an oxygen plasma to selectively etch approximately 2.3 mm of polycarbonate, leaving the gold nanotubes intact.[15] Figure 1 shows images from field-emission scanning electron microscopy (SEM) of the top surface of a template membrane after electroless deposition of gold followed by RIE. The images in Figure 1 reveal a high level of surface roughness; the length scale is % 53 nm. The membrane reactor used to study CO oxidation over gold nanotubes is shown schematically in Figure 2.[12] Table 1 shows results for the rate of...

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Oxidation-Resistant Gold-55 Clusters

Cited by 499 publications

References 18 publications

Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO₂ Catalyst under Oxidative and Reducing Atmospheres

Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO₂ Catalyst under Oxidative and Reducing Atmospheres

Weighing Supported Nanoparticles: Size-Selected Clusters as Mass Standards in Nanometrology

Gold‐Nanotube Membranes for the Oxidation of CO at Gas–Water Interfaces

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Oxidation-Resistant Gold-55 Clusters

Cited by 499 publications

References 18 publications

Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO2 Catalyst under Oxidative and Reducing Atmospheres

Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO2 Catalyst under Oxidative and Reducing Atmospheres

Weighing Supported Nanoparticles: Size-Selected Clusters as Mass Standards in Nanometrology

Gold‐Nanotube Membranes for the Oxidation of CO at Gas–Water Interfaces

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Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO₂ Catalyst under Oxidative and Reducing Atmospheres

Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO₂ Catalyst under Oxidative and Reducing Atmospheres