AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS3-MoA

Paper SS3-MoA10
Electronic Detection of Oscillatory Reactions on Supported Platinum Particles

Monday, November 3, 2003, 5:00 pm, Room 328

Session: Structure and Reactivity of Metal Clusters
Presenter: M.C. Wheeler, University of Maine
Authors: M.C. Wheeler, University of Maine
R.E. Cavicchi, National Institute of Standards and Technology
S. Semancik, National Institute of Standards and Technology
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A MEMS device, capable of surface temperature control and electrical resistance measurements, has been used to detect and explore the oscillatory reaction of CO oxidation on oxide-supported platinum particles. The behavior has been monitored for a range of conditions, but as an example, when the supported platinum is heated to 165°C in a 340 ppm CO/air mixture at atmospheric pressure, periodic switching between a low-resistance (excess CO) state and a high-resistance (excess oxygen) state is observed. During these cycles, the resistance ranges from 7.1 k@ohm@ to 17. k@ohm@ and back to 7.1 k@ohm@ over a period of 200 s. The resistance switching that we have studied on small (on the order of 30 nm) platinum particles is likened to the temporal oscillations of the reaction on platinum films@footnote 1@ and single crystal samples,@footnote 2@ which were monitored by infrared and photoemission electron microscopy respectively. We have shown that the frequency of the resistance oscillations can be manipulated by varying the CO partial pressure in order to influence the rate of CO uptake. Also, synchronization observed between oscillations for physically separate devices in multi-element arrays is evidence that the oscillations are due to a globally-coupled, mass-transfer and reaction rate effect. Indeed, effects such as doubling of the oscillation frequency on neighboring devices are similar to the rate behavior observed by Yamamoto et al. In addition to the global synchronization, transient oscillations are observed prior to switching that suggests microscale-coupling occurs between the individual platinum particles on the support. @FootnoteText@@footnote 1@ Yamamoto, Surko, and Maple, J. Chem. Phys. 103, 8209 (1995).@footnote 2@ G. Ertl, Science 254, 1750 (1991).