Cluster size dependence of a cluster property χ(n) on the number n of cluster constituents. The data are plotted vs n− β , where β ≥ 0 is a system-specific parameter. Reprinted with permission from Jortner and Rao, Pure Appl. Chem. 74, 1491 (2002). Copyright 2002, IUPAC.
(Color online) X-ray absorption spectroscopy setup at beamline X18A at the National Synchrotron Light Source (Brookhaven National Laboratory).
(Color online) Raw EXAFS data for Pt nanoparticles supported on high surface area γ-Al2O3 substrate and bulk Pt (a) in energy, (b) in k-space, and (c) in r-space. The inset in (c) shows a model of a truncated cuboctahedral cluster and different groups of atomic arrangements that contribute to different peaks in r-space.
(Color online) Effects of the average particle size on the Pt-Pt bond length (a), mean square disorder (b) and near-edge region (c) for γ-Al2O3-supported Pt nanoparticles under He flow. Adapted with permission from Sanchez et al., J. Am. Chem. Soc. 131, 7040 (2009). Copyright 2009, American Chemical Society.
(Color online) Effects of the atmosphere (H2, He or O2) on the Pt-Pt bond length (a), mean square disorder (b), and near edge region (c) for γ-Al2O3-supported Pt nanoparticles with an average size of 0.9 nm. Adapted with permission from Sanchez et al., J. Am. Chem. Soc. 131, 7040 (2009). Copyright 2009, American Chemical Society.
(Color online) Effects of the support (γ-Al2O3 or C) on the Pt-Pt bond length (a), mean square disorder (b), and near-edge region (c) for γ-Al2O3-supported Pt nanoparticles of similar average sizes (0.9 and 1.0 nm) and under He flow. Adapted with permission from Sanchez et al., J. Am. Chem. Soc. 131, 7040 (2009). Copyright 2009, American Chemical Society.
(Color online) Effects of adsorbate-metal, support-metal, and adsorbate-support interactions on the charge state of supported metal nanoparticle. Reprinted with permission Small et al., ACS Nano 6, 5583 (2012). Copyright 2011, American Chemical Society.
(Color online) Schematics of the effects of metal-adsorbate interactions on the shape of supported metal particles (see Ref. 26 for details).
(Color online) Effects of the adsorbate partial pressure on the integrated area (“Signal”) under the ΔXANES data (obtained by subtracting the 673 K data from that of the actual temperatures). The signal shows a strong dependence on pressure and temperature, in qualitative agreement with theoretical expectations [Eq. (2) ]. Reprinted with permission Small et al., ACS Nano 6, 5583 (2012). Copyright 2011, American Chemical Society.
(Color online) Trajectories of the center of mass (full lines) and cluster footprint (fuzzy shading) projected onto the support, at 165 K (left) and 573 K (right) for Pt10 nanoparticles on γ-Al2O3. The circles indicate the positions of the O and Al atoms with full circles corresponding to O atoms in the top support layer and shaded ones to the second layer. The trajectories show the 1–2 Å amplitude “rattle” motion of the clusters as well as long “roll” events, especially at higher temperature. The intensity of the footprint indicates that the clusters have a tendency to remain in certain areas of the support, and that at higher temperature the area of contact is notably larger.
(Color online) Experimental and theoretical Pt L3 edge XANES of Pt nanoparticles on γ-Al2O3 at 165 and 573 K. The error bars of the theoretical results indicate the standard deviations of the spectra due to the dynamical disorder of the nanoparticles. Adapted with permission from Vila et al., Phys. Rev. B 78, 121404 (2008). Copyright 2008, American Physical Society.
(Color online) Development of the spatial resolution of optical and electron microscopes. The current rapid improvement in resolution is due to the development of aberration correctors for the electromagnetic lenses, with the current best point-to-point spatial resolution of 0.5 Å (Ref. 179 ).
(Color online) Cs-corrected HAADF STEM images of Pd-Pt nanoparticles. Image of (a) a Pt(core)-Pd(shell), (b) a Pd(core)-Pt(shell), and (c)a coreduced Pt/Pd nanoparticle with labeled crystal facets and the areal integrated intensity measurement made within the boxed region. Corresponding power spectrum data and integrated intensity profile measurement shown as the inset in (d-f). Adapted with permission from Sanchez et al., J. Am. Chem. Soc. 131, 8683 (2009). Copyright 2009, American Chemical Society.
(Color online) Surface faceting of a Cu nanoparticle supported on ZnO in various gas environments [(a), (d) pure H2; (b), (e) a mixture of H2:H2O = 3:1; and (c), (f) a mixture of 95% H2 and 5% CO], where (a), (b), and (c) are in situ HREM images and (d), (e), and (f) are the corresponding Wulff constructions. The data were measured under a total pressure of 1.5 mbar (a), (b), (d), (e) or 5 mbar (c), (f), respectively, and a temperature of 220 °C. Adapted with permission from Hansen et al., Science 295, 2053 (2002), Copyright 2002, AAAS.
Au nanoparticles supported on CeO2 in (a) vacuum and (b) 1 volume% CO in air at 45 Pa and room temperature. Two (100) facets are indicated by I and II in (a). The enlarged images of these regions in vacuum and in the CO/air mixture are shown at the bottom of (a) and (b), respectively, revealing changes in the distance between the first and the second (100) surface layers as well as the (200) planes in crystalline bulk gold. These changes in positions of the Au atomic columns correspond well to those of the Au (100) reconstructed surface structure. Reproduced with permission from Yoshida et al., Science 335, 317 (2012). Copyright 2012, AAAS.
Bright field TEM images of Au nanoparticles in N2 (1.1 atm) taken on an FEI Titan at 300 kV using an in situ TEM gas flow specimen holder by Hummingbird Scientific.
(Color online) Typical size distribution histogram obtained by TEM for model systems of supported metal clusters. The distribution symbolizes a collection of different structural motifs in real catalytic systems. Shown are cartoons of ordered and disordered clusters that will be observed in each size range. Note the expected transition zone between 1 and 1.5 nm: the ordered (O) and disordered (D) clusters are known to coexist in this range. The chart on the right shows our proposed new investigation method of heterogeneous catalysts: Distributions of particle sizes and compositions will be obtained by in situ TEM. Theoretical thermodynamic properties will be calculated for each type of cluster in the distribution and averaged with the experimentally measured distribution. XAS studies of the average pressure and temperatures under which the catalyst operates will be used to validate the theoretical calculations.
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