Design of catalysts with artificially controllablefuntions using surface acoustic waves and resonance oscillations generated on ferroelectric materials

摘要

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 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.