Theoretical Explanation of Pt Trimers Observed by Z-Contrast STEM


First-principles quantum-mechanical calculations on γ-alumina have revealed a fascinating “reactive sponge” phenomenon. γ-alumina can store and release water, but in a unique, “reactive” way. This “reactive sponge process” facilitates the creation of aluminum and oxygen vacancies in the alumina surface. Earlier atomic-resolution Z-contrast STEM images of ultradispersed Pt atoms on a γ-alumina support showed the individual atoms to form dimers and trimers with preferred spacings and orientations that are apparently dictated by the underlying support[1]. In turn, the reactive sponge property of γ-alumina is the key to understanding the Pt clusters. Our calculations demonstrate that if three Pt atoms fill three vacancies created during the reactive sponge process, the resulting geometry precisely matches that of the Pt trimers observed in the Z-STEM images. Understanding the initial nucleation of small clusters on the complex gamma alumina surface is an essential first step in determining the origins of catalytic activity.

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This research was sponsored by the Laboratory Directed Research and Development Program (SEED) of Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U. S. Department of Energy under Contract No. DE-AC05-960R22464, National Science Foundation grant DMR-9803768, by the William A. and Nancy F. McMinn Endowment at Vanderbilt University, and by financial support from Dupont through an ATE grant. Computations were partially supported by the National Center for Supercomputing Applications (NCSA) under grant CHE990015N to KS and utilized the SGI Origin2000 at NCSA, University of Illinois at Urbana-Champaign. KS was supported by an appointment to the ORNL Postdoctoral Research Program administered jointly by ORNL and Oak Ridge Associated Universities.

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Sohlberg, K., Pantelides, S.T. & Pennycook, S.J. Theoretical Explanation of Pt Trimers Observed by Z-Contrast STEM. MRS Online Proceedings Library 589, 241 (1999).

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