Effects Of Resonance Oscillation Research Articles

Effects of resonance oscillation with a thickness-extensional mode on activation of thin film metal and metal oxide catalysts deposited on poled ferroelectric substrates

The effects of resonance oscillation (RO) with a thickness-extensional mode generated in a poled ferroelectric z-cut LiNbO 3 single crystal by rf power were studied on reaction selectivity for the ethanol decomposition of thin film Au, Ag and WO 3 catalysts deposited. For a 100 nm Ag catalyst, a 3.5 MHz RO at 3 W caused an increase in ethylene production at 573 K by a factor of 16 without any change in acetaldehyde production. The selective promotion of ethylene production by RO was also observed at 573 K for a Au catalyst in which the activity for ethylene production increased by a factor of 5. For a WO 3 catalyst the RO increased both the ethylene and acetaldehyde productions, but the former was more largely promoted than the latter. The RO caused decreases in respective activation energy. The selective production of ethylene is associated with the RO-induced strong oxygen–metal (and metal oxide) surface interactions which are produced by dynamic lattice displacement.

Anomalous enhancement of catalytic activity over a Pd thin film by the effects of resonance oscillation generated on a ferroelectric substrate

A poled ferroelectric lithium niobate single crystal ( z-cut) was employed as a substrate, on the planes of which either a catalytically active Pd or an inactive Al metal was deposited at a thickness of 100 nm. Resonance characteristics were measured, and the effects of resonance oscillation on the catalytic activity for ethanol oxidation were examined. For the Al metal, a negligibly small enhancement of the activity occurred at 343 K, whereas, for the Pd metal, the activity increased dramatically with increasing power at a resonance frequency of 3.4 MHz and amounted to 1880 times larger activity at 3 W. The activation energy of the reaction decreased from 156 to 12 kJ mol −1 with power-on. No activity increase was observed at non-resonance frequency. The effects of resonance oscillation on catalytic activity are discussed.

Effects of resonance oscillation on catalytic activity of a thin Pd film deposited on polar ferroelectric surface

A ferroelectric lead strontium zirconium titanate (PSZT) disc having a single domain structure was employed as a substrate, on which a catalytically active Pd metal was deposited as a thin film with a thickness of 50 nm. The catalytic activity for ethanol oxidation on a Pd PSZT catalyst increased by a factor of 10–460 by imposing voltages at a resonance frequency of PSZT. The frequency dependence showed that the activity increase occurred only at a resonance oscillation. With an increase in voltage, the activity increased monotonically. A laser Doppler method showed that only the resonance oscillation caused a significant lattice displacement due to a radial extensional mode of PSZT, which is considered to be responsible for the anomalous activation of the catalyst.