AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM11
A Model Catalyst with Selectivity Controllable Functions: The Effects of Frequency in Thickness Extension Mode Resonance Oscillation on Ethanol Decomposition Over a Thin Ag Film Deposited on a Ferroelectric z-cut LiNbO@sub 3@ Single Crystal

Tuesday, November 5, 2002, 11:40 am, Room C-108

Session: Hydrocarbon Catalysis
Presenter: N. Saito, Nagaoka University of Technology, Japan
Authors: N. Saito, Nagaoka University of Technology, Japan
Y. Yukawa, Nagaoka University of Technology, Japan
H. Nishiyama, Nagaoka University of Technology, Japan
Y. Inoue, Nagaoka University of Technology, Japan
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The resonance oscillation of acoustic waves is generated on a poled ferroelectric crystal by a piezoelectric effect. We have shown that the thickness extension mode resonance oscillation (TERO) has the ability to remarkably change the reaction selectivity over thin metal catalysts deposited on a z-cut LiNbO@sub 3@ (z-LN) crystal.@footnote 1@ The TERO has a series of resonance frequencies (the first, the second, the third and so on) determined by the crystal constants. A z-LN crystal shows 3.5(first), 10.8 (second) and 17.9 (third) MHz. It is interesting to see the frequency effects on TERO-induced selectivity changes. In the present work, the TERO of 10.8 and 17.9MHz were employed for ethanol decomposition on a thin Ag film catalyst deposited, and the results were compared with those reported previously for 3.5MHz. The TERO of 10.8 and 17.9 MHz at 1.5W caused the enhancement of ethylene production without significant changes in acetaldehyde production. The selectivity for ethylene production, S@sub e@, increased from 62% without the TERO to 96% for 3.5MHz, 85% for 10.8MHz and 75% for 17.9MHz. The selectivity increases became small with increasing resonance frequency. Laser Doppler measurements showed that the TERO generated randomly distributed standing waves vertical to the surface. With increasing frequency, the magnitude of the waves, corresponding to lattice displacement, decreased (98 nm for 3.5 MHz, 28 nm for 10.8 MHz and 15 nm for 17.9MHz at 1W), whereas the number of the standing waves per unit area increased remarkably. In photoelectron emission spectroscopy, the TERO shifted the threshold energy of photoelectron emission from Ag surface by 0.08-0.25eV. The present results indicate that the magnitude and the density of standing waves strongly related to activity enhancement and selectivity changes. A mechanism of the frequency-dependent TERO effects is discussed. @FootnoteText@ @footnote 1@ N.Saito and Y.Inoue, J.Chem. Phys. 133,469(2000).