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  English.dicp.cas.cn    Posted:2013-06-07
The Reactivity and Structural Dynamics of Supported Metal Nano-Clusters using Electron Microscopy, in situ X-ray Spectroscopy, and Electronic-Structure Theory and Simulations

Time:2013.6.8  10:00

Location:Meeting Room of Catalysis Building

Lecturer:Pro. Judith C. Yang

Department of Chemical and Petroleum Engineering

Department of Physics,University of Pittsburgh,Pittsburgh,PA,USA

Introduction:

Professor Judith C Yang received her PhD in physics from Cornell University in 1993. She then went to the Max-Planck-Institute of Metallforschung, Stuttgart, Germany as a post-doctoral fellow. In 1995, she returned to the US as a post-doc and visiting lecturer to the Materials Research Laboratory, U. Illinois at Urbana-Champaign. In 1999, she joined the materials science and engineering faculty at U. Pittsburgh. She has authored or co-authored ~60 journal publications and given ~90 invited talks. She is the 2002 recipient of the NSF career award, 2004 B.P. America Faculty fellowship, and the 2005 Chancellor’s Distinguished Research Award. Since 2010, she is a Professor in Chemical and Petroleum Engineering; she has a secondary appointment in physics. Her research areas include oxidation, heterogeneous catalysis, nano-materials, gas-surface reactions, and transmission electron microscopy, especially in situ.

Abstract:

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. XAFS technique is one of the premiere tools to study both atomic and electronic structure of small ensembles due, in part, to its local structure sensitivity and excellent spatial resolution. During the last decade, our collaborative effort at Brookhaven Lab’s synchrotron source (NSLS) resulted in developing both the state-of-the-art experimental facility for in situ reaction studies, and the analysis procedure to study mono- and hetero-metallic nanoparticles. Complimentary information on site-specific structure and chemistry can be obtained by quantitative (scanning) transmission electron microscopy ((S)TEM), which has a unique capability for providing structural and spectral information simultaneously. We have recently advanced this imaging method of STEM by correlating the absolute image intensity to the scattering cross-section. Utilizing and developing state of the art electron and X-ray probe methodologies, we will explore substrate/nanoparticle interactions as a function of support and nanoparticle material, as well as by size, composition and 3-D structure of the supported nanoparticle. 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. To bridge the theory-experiment gap, we are producing model Pt/-Al2O3 systems using oxidation of NiAl(110) to form a

Contact:501 Na Ta(9251)

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