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

Abstract

The effects of thickness extension mode resonance oscillation (TERO) of acoustic waves on the catalytic properties of a 100 nm thick Pd film deposited a positively polarized ferroelectric z-cut LiNbO 3 single crystal were studied. For ethylene and acetaldehyde production in ethanol decomposition, the TERO accelerated ethylene production only and enhanced the selectivity for ethylene production from 40% to 96%. Randomly distributed standing waves due to large lattice displacement vertical to the surface were generated with TERO on. The photoelectron emission spectra showed that the TERO caused a positive shift of the threshold energy of photoelectron emission from a Pd surface, indicating an increase in the work function of the surface. The TERO effects on a Pd catalyst were compared with those previously observed for a Ag catalyst.

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

“…In previous studies, the positive work function shifts were found to increase with increasing rf power, [13][14][15] which indicated that large vertical lattice displacement was responsible for large work function shifts. Because large vertical lattice displacement occurred at low resonance frequency, compared to high frequency, it is apparent that the low frequency was able to cause large positive work function shifts, and hence the TERO effects became larger in low frequency than in high frequency.…”

“…[13][14][15] Based on the findings, a mechanism for TERO effects on work function was proposed. The work function of a transition metal is mainly determined by the barrier of an electric double layer that is formed by electrons spilled out from the topmost layer of a metal surface and positive charges remaining in the interior of the bulk metal.…”

“…We have previously performed photoelectron emission spectroscopic studies and have found that the TERO caused the positive shifts of threshold energy of photoelectron emission from Ag and Pd metal catalysts. − Based on the findings, a mechanism for TERO effects on work function was proposed. The work function of a transition metal is mainly determined by the barrier of an electric double layer that is formed by electrons spilled out from the topmost layer of a metal surface and positive charges remaining in the interior of the bulk metal. , Our assumption is that vertical lattice displacement by the TERO increases the density of “spill out” electrons, thus changing the electric double layer so as to cause positive work function shifts.…”

“…The differences were associated with the findings that the positive work function shifts caused by the TERO were larger for (+)Ag than for (−)Ag. The polarization-dependent TERO effects on catalytic and surface properties also existed for (+)Pd and (−)Pd catalysts. , …”

“…The polarization-dependent TERO effects on catalytic and surface properties also existed for (+)Pd and (-)Pd catalysts. 7,15 In all the studies of TERO effects, we have used the first primary resonance frequency of 3.5 MHz only. For further development of acoustic wave excitation effects on metal catalysts and for better understanding of the mechanism, it is of particular importance to clarify the effects of resonance frequency, that is, to see how different resonance frequencies affect the catalytic and surface properties.…”