Design of Catalysts with Artificially Controllable Functions Using Surface Acoustic Waves and Resonance Oscillations Generated on Ferroelectric Materials

A poled ferroelectric material of a LiNbO 3 single crystal and a polycrystalline lead strontium zirconium titanate(PSZT) disc were employed as a catalyst substrate, on which various metals such as Pd, Ag, Ni and Pt and a WO 3 oxide were deposited as a thin film catalyst. The effects of acoustic waves generated by rf power upon catalyst activation and reaction selectivity have been examined. The activity for CO oxidation of a Pt/PSZT catalyst increased by a factor of 3.9 with a thickness-extensional(TE) mode of resonance oscillation(RO) and 2.9 with a radial-extensional (RE) mode. The activation energy of the reaction was larger for the TE mode( 38 kJmol −1 ) than that for the RE mode(24 kJmol −1 ). The polarization axis-dependent changes in surface potential occurred with the TE mode, but not with the RE mode. With the TE mode, the activation energy of ethanol oxidation over a Ni/LiNbO 3 and a Ag/LiNbO 3 catalyst decreased from 36 to 19 kJmol −1 and from 76 to 30 kJmol −1 , respectively, and the TE mode had a larger effect on the reaction with a higher activation energy. In ethanol dehydrogenation and dehydration on a WO 3 / LiNbO 3 catalyst, the TE mode increased remarkably the selectivity for ethylene production without giving a significant change to acetaldehyde production. The effects of acoustic wave excitations on the catalysts are discussed.