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: 4 of 6
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UIUC) of Pd-rich Cu nanoparticle, where a core-shell structure is not observed.
EXAFS measurements of coordination numbers in nanoclusters contain size- and shape-specific
information. For bare metal clusters, a number of different minimum-energy, regular polyhedral
12 12 , , , ,geometries are
A B 9 C P often proposed as
8 -n . AuAu . AuAu structural motives.
U 0z We have developed
4 4k a suite of computer
o 1.0~cluster geometry
0.0 0.4 0.6 0.8 1.0 0 0.2 0.4 0.6 0.8 1.0 . 0.2 0.4 0.6 0.8 for most
XA XPd Xpdgeeainfrms
Figure 5: Coordination numbers in nanoalloys: model of a random alloy (A), quasi- regular polyhedra,
random dendrimer-stabilized Pd/Au alloys (B), and core-shell alloys (C). Samples: R. as well as a data
M. Crooks. U. of Texas at Austin analysis package to
coordinates and obtain radial distribution function information that can be directly compared with
experiment. For bimetallic alloys, our methods of multiple-edge, constrained fits can discriminate
between quasi-random and core-shell structures (Fig. 5).
5) DFT modeling of ligand-stabilized Au13 nanoclusters (DE
FG02-03ER15475, DE FG02-03ER15476, DE FG02-03ER15477).:
We simulated thiol/phosphine-stabilized Au13 nanoclusters via
DFT (collaborator: L. Kronik, Weizmann Inst.), and compared
structure/ligand placement patterns with recent EXAFS/TEM
measurements of these clusters. The structural model that is in a
good quantitative agreement with experiments corresponds to a
distorted icosahedral structure by on-top phosphine ligands and a
combination of on-top and bridging thiol ligands (Fig. 6). The
ligand-induced bond-length disorder is predominantly tangential,
not affecting radial Au-Au distances.
6) Supported core-shell Ir-Pt nanoparticles on A1203
prepared from a molecular cluster precursor: structure and Figure 6: Optimized Au13 structure.
dynamics determined using STEM, HRTEM and EXAFS
(DE FG02-03ER15475, DE FG02-03ER15476, DE FG02-03ER15477):
Addition of Re or Ir to Pt/A1203 petroleum reforming catalysts enhances catalytic activity, increases the
octane rating of the fuel product, and reduces deactivation of the catalyst due to coking. In many systems,
the properties that emerge exceed those expected from an additive combination of the behavior of the
monometallic components, and this synergistic enhancement of catalyst performance has been attributed
to a combination of geometrical and electronic effects. The presence of both metals on the surface
provides a variety of chemically and geometrically different binding sites for reactant adsorption and
consequent reaction. Additionally, strain induced by lattice mismatches of the component metals can
modify the intermetallic distances and affect adsorption energetics. Lastly, charge transfer from one
metal to another and orbital rehybridizations induced by
Scheme i bimetallic bonding can impact the electronic structure of the
bimetallic system and alter the energetics of catalysis. In some
S o H, 673 K systems, the addition of the second metal dramatically inhibits
Ut co sintering of the nanoparticles under reactive conditions. The
deposition of the bimetallic cluster [Ir3Pt3( -CO)3(CO)3-
C5Me5)3] on y-A1203, followed by reduction with hydrogen,
iICO-e [i I-A results in highly-dispersed supported bimetallic Ir-Pt
* Ir o pt
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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/m1/4/: accessed July 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.