When 10:30 AM - 11:30 AM Apr 08, 2016
Where 1670 Beyster Building
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Structural Dynamics of Supported Metal Nano-Clusters

Judith Yang
Department of Chemical and Petroleum Engineering, University of Pittsburgh

Heterogeneous catalysis, which impacts the worldwide economy and sustainability due to its ubiquitous role in energy production, depends sensitively on the nano-sized 3-dimensional structural habits of nanoparticles (NPs) and their physicochemical structural sensitivity to the environment. Very small metal clusters can exhibit patterns of reactivity and catalytic activity that are dramatically distinct, and sometimes completely opposite, than behaviors seen with larger clusters. It therefore remains a significant need in research to fundamentally understand and predict the local structure and stability of catalytic materials that can be specifically tailored by design and optimized for an application in technology. Our focus is on the development of integrated characterization and modeling tools and their applications appropriate for carrying out detailed studies on metallic nanoscale clusters comprised of a few to as many as 100 metal atoms. Two state of the art methodologies, synchrotron X-ray absorption fine-structure (XAFS) and quantitative scanning transmission electron microscopy (STEM) methodologies are used and specially designed for determining the 3D structure and structural habits, both individually and as an ensemble, critical for understanding metallic nanoclusters. The experimental work is integrated with theoretical calculations. It is now clear that the structural dynamics of small metallic clusters is actually quite complex. For example, we have shown that the structures of Pt NPs may be both ordered and disordered, depending on its size, support and adsorbates. While bulk amorphous Pt is unstable, its existence in NPs is a manifestation of their mesoscopic nature. Furthermore, theoretical simulations show that the Pt NPs are not static, but show highly fluxional dynamics

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