Journal of Physical Chemistry B, Vol.107, No.9, 2040-2045, 2003
Effects of thickness extension mode resonance oscillation of acoustic waves on catalytic and surface properties. IV. Activation of a Ag catalyst for ethanol decomposition by overtone resonance frequencies
The effects of resonance frequencies of acoustic waves on catalytic and surface properties were studied. The overtone resonance frequencies of 3.5, 10.8, and 17.9 MHz were applied to a 100 nm thick Ag catalyst deposited on a ferroelectric z-cut LiNbO3 crystal which generated thickness extension mode resonance oscillation (TERO). For ethanol decomposition, the TERO enhanced ethylene production without significant changes in acetaldehyde production for all the frequencies. The extent of catalyst activation strongly depended on the resonance frequency. In a low power region (<0.8 W), the TERO effect had a maximum at the middle of frequency, whereas in a high power region (>1.0 W), it increased in the order 3.5 > 10.8 > 17.9 MHz. The activation energy for ethylene production decreased remarkably in the presence of TERO, the extent of which strongly depended on the frequency. Laser Doppler measurements showed that with increasing resonance frequency, the number of standing waves increased markedly, whereas the amplitudes of the wave decreased considerably. The specific catalytic activity, defined as the activity enhancement per the density of wave, increased in a nonlinear manner with lattice displacement. The resonance frequency effects of TERO on catalyst activation are discussed.