Effects of Thickness Extension Mode Resonance Oscillation of Acoustic Waves on Catalytic and Surface Properties I. Ethanol Decomposition on a Thin Ag Film Catalyst Deposited on Positively Polarized Z-Cut LiNbO3

Abstract

A 100-nm thick Ag film was deposited on a positively polarized z-cut LiNbO3 ferroelectric substrate, and the effects of thickness extension mode resonance oscillation (TERO) of bulk acoustic waves generated by rf electric power on the catalytic properties were studied. In ethanol decomposition, the TERO caused a remarkable increase in ethylene production without changes in acetaldehyde production, and the activation energy for ethylene production decreased considerably. The activity for ethylene production increased in a nonlinear manner with increasing rf power, and its selectivity resulted in a marked enhancement. A laser Doppler method demonstrated that the TERO produced randomly distributed standing waves with large lattice displacement vertical to the surface. In photoelectron emission spectra, the TERO caused a positive shift of the threshold energy in photoelectron emission from the Ag surface, which was indicative of an increase in a work function-related parameter in the presence of TERO. The vertical dynamic lattice displacement is proposed to be responsible for positive work function shifts. Correlation existed between activity enhancement and the work function shift, which indicated that activity enhancements with TERO are associated with increases in the work function. A mechanism of TERO effects on selectivity changes is discussed.