The Reactivity and Structural Dynamics of Supported Metal Nanoclusters Using Electron Microscopy, in situ X-Ray Spectroscopy, Electronic Structure Theories, and Molecular Dynamics Simulations. Page: 3 of 6
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particles and provide bulk-scale access to this most important example of a system displaying rate
sensitivities arising due to the consequences of strong metal support interactions. Both reactive oxygen
species, ozone and atomic oxygen, significantly reduced the amount of agglomeration of the Au clusters
as compared to annealing at 400 C (2.7 0.6 nm, 324+264 atoms), where ozone produced the smallest
clusters (1.2 0.5 nm, 40+49 atoms). The Au particles formed after 5 eV atomic oxygen exposure
revealed a broad size distribution (2.1+0.7 nm, 72 98 atoms) with an average size in between those
produced by the two prior treatments. Fig.1 shows the HRTEM images from different Au particles on
(b) 0.50 0.22 nm
(c) 4-Ir-X -
N=3.4 0.6 - Fit
N=2.4 0.5 r
020304060708091011121314 0 2 4 6 8 10
Diameter (nm) R (A)
Figure 3: (a) A HAADF (Z-contrast) image of Ir nanoclusters with diameters less 1 nm diameters
mostly; the size distribution of Ir clusters in (b) is, to a good approximation, monodisperse. It is a
central assumption made in EXAFS analysis in (c) which showed good agreement with the STEM
results for the cluster diameter.
TiO2 after atomic oxygen exposure, revealing a variety of structures including bilayer rafts (a), faceted
hemispheres (b) and spherical shapes (c).
3) Combined HREM, STEM and EXAFS structural characterization of ultra-small Ir and Ni
hydrogenation catalysts. (DE FG02-03ER15475, DE FG02-03ER15477) "Ziegler-type hydrogenation
catalysts", such as Ni and Co, are used for polymer hydrogenation in industry to hydrogenate 100 million
pounds of polymer per year, and Ir is a model for these industrial catalysts. Recently, very small Ir, Ni
and Co nanoparticles containing approximately 4-6 atoms, were synthesized by Prof. Richard Finke's
group at Colorado State University. All of the samples were characterized by HREM, STEM and
EXAFS, where very small sizes were noted for both the Ir and Ni, but the observed Co particle sizes were
larger probably due to coalescence. Most of the Ni and Ir particles had diameters less than 0.5 nm,
corresponding to clusters with 4-6 atoms, but some particles were close to 1 nm in size. Figure 3 is a
HAADF image from Ir sample, which (a) shows Ir clusters with less than 0.5 nm; (b) with around 0.7 nm;
(c) some clusters as large as about mnm in diameters. EXAFS analysis was
performed, guided by TEM information about cluster monodispersity. The
EXAFS results allowed us to develop a 3D model of the Ir clusters.
Figure 4: Atomic
image of a Pd-rich:Cu
nanoparticle. Courtesy of
M. Ghass (SuperSTEM,
4) Development of self-consistent methods of structural investigation
(size, structure, degree of alloying) of bimetallic catalysts by combined
STEM and EXAFS. (DE FG02-03ER15475, DE FG02-03ER15476, DE
FG02-03ER15477). The distribution of elements within a single
nanoparticle is critical to determine, such as homogeneous distribution or
core-shell. We have examined Pd-Cu bimetallic catalysts with varying
relative amounts of Pd:Cu (100% Pd to 50% Pd:Cu), as a promising
catalyst to reduce nitrates from drinking water. Figure 4 is a HAADF
image from an aberration-corrected STEM (where one now exists at
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Yang, Judith C. & Ralph G. Nuzzo, Duane Johnson, Anatoly Frenkel. The Reactivity and Structural Dynamics of Supported Metal Nanoclusters Using Electron Microscopy, in situ X-Ray Spectroscopy, Electronic Structure Theories, and Molecular Dynamics Simulations., report, July 1, 2008; Pittsburgh, Pennsylvania. (digital.library.unt.edu/ark:/67531/metadc901032/m1/3/: accessed December 11, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.