Structure and Dynamics in Ligand-Protected and Supported Metal Nanoparticles

This dissertation describes the use of x-ray absorption spectroscopy (XAS) and advanced electron microscopy methods to develop fundamental understandings of nanoparticle structure. Analysis of the x-ray absorption spectra provides structural information with 0.001 A precision. Quantitative high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) measurements characterize metal clusters and nanoparticles on the basis of the number of metal atoms they contain. Ligand-protected 13-atom gold clusters serve as a model system to illustrate the capabilities of a correlated use of these techniques. They exhibit a molecular density of electronic states and non-bulk icosahedral structure. These gold clusters are further used as precursor in the preparation of titania-supported gold oxidation catalysts via ligand removal using ozone or thermal treatments. The capability of the quantitative HAADF-STEM analysis for the determination of nanoparticle shape is demonstrated in these studies. X-ray absorption spectroscopy studies of sub-nanometer gamma-alumina-supported platinum nanoparticles revealed unprecedented metal-metal bond contraction with increasing temperature. Both the structural and electronic information obtained in the spectroscopic studies suggest that support-particle charge transfer is responsible for these dynamic effects. Supported bimetallic iridium-platinum nanoparticles were also prepared via reduction of a bimetallic cluster precursor. This preparation allowed excellent control of nanoparticle size and compositional distributions as the stoichiometry of the cluster precursor was retained. This was confirmed analytically using energy dispersive x-ray (EDX) spectroscopy of individual nanoparticles. XAS studies revealed that the bimetallic nanoparticles assumed a core-shell structure with an iridium-rich core and a platinum-rich shell. The implementation of a novel analysis method that accounted for the overlap of the iridium and platinum absorption edges allowed the determination of structural parameters with low uncertainties and a consequently well-characterized structural model.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Menard, Laurent D., Jr

Contributors dc:contributor

• Nuzzo, Ralph G.

• Engineering, Materials Science

Language dc:language

eng

Identifier

(MiAaPQ)AAI3250290

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/87889