Application of Resonance Oscillation to the Design of Heterogeneous Catalysts with Artificially Controllable Functions for Chemical Reactions

射频电功率作用于极化铁电晶体产生的体声波共振振荡(RO)会引起金属薄膜表面的动态变形。在Ag和Pd催化剂上C_2H_5OH和CO的氧化以及C_2H_5OH的分解中，厚度扩展模式RO(Tero)不仅具有提高催化活性的能力，而且还具有提高反应选择性的能力。相反，厚度-剪切模式共振(TSRO)没有表现出激活效应。激光多谱勒和光电子能谱测量表明，TSRO引起了金属催化剂表面垂直于表面的较大晶格位移，并引起了功函数的变化，而TSRO没有发生这种变化。Tero效应对催化剂活性的影响取决于铁电衬底的极化方向和共振频率，表明大的垂直晶格位移和引起晶格位移的位置密度是催化剂强烈活化的原因。Ag和AgAu合金催化剂在乙醇分解反应中的Tero效应存在本质差异。Tero诱导的活化只发生在银金属上的乙烯生成，而Tero效应强烈依赖于合金成分。生成乙烯的活性几乎与合金组成无关，但生成乙醛的活性在表面Au含量约为80%时出现最大值，此时垂直晶格位移最小。因此，在Ag-Au原子相互作用变强的情况下，AgAu二元合金催化剂上的Tero效应对乙醛合成的影响增强。金属多相催化中的RO效应是一种新现象，对开发具有人工可控功能的多相化学反应催化剂具有重要意义。

Resonance oscillation (RO) of bulk acoustic waves generated by piezoelectric effects on poled ferroelectric crystals by rf electric power causes the dynamic distortion of thin metal film surfaces deposited. In C_2H_5OH and CO oxidation and C_2H_5OH decomposition on Ag and Pd catalysts, thickness-extension mode RO (TERO) was found to have a capability of enhancing not only catalytic activity, but also reaction selectivity. In contrast, thickness-shear mode resonance oscillation (TSRO) showed no activation effects. Laser Doppler and photoemission spectroscopic measurements showed that TERO caused large lattice displacement vertical to the surface and to induce work function shifts of the metal catalysts, whereas no such changes occurred with TSRO. The TERO effects on catalyst activation depended on the polarization direction of ferroelectric substrates and resonance frequency, indicating that large vertical lattice displacement and the density of sites causing lattice displacement are responsible for strong catalyst activation. The TERO effects were intrinsically different in ethanol decomposition between Ag and AgAu alloy catalysts. TERO-induced activation occurred only for ethylene production on a Ag metal, whereas TERO effects had strong dependence on alloy compositions. The activation for ethylene production was nearly independent of alloy composition, but that for acetaldehyde production exhibited a maximum at around 80% surface Au content where the vertical lattice displacement became the smallest. Thus, it was proposed that the TERO effects on acetaldehyde production over the AgAu binary alloy catalysts increased in the case where Ag-Au atom interactions became strong. The RO effects on heterogeneous catalysis by metals are new phenomena and are concluded to be quite useful for the development of a heterogeneous catalyst with artificially controllable functions for chemical reactions.