Effects of Resonance Oscillation on Activation of Thin film Catalysts Deposited on a Ferroelectric Substrate

在设计具有人工可控功能的多相催化剂的尝试中，应用了通过施加射频电功率在铁电晶体上产生的共振振荡现象。采用极化的铁电单晶铌酸锂（LiNbO_3）作为衬底，在其上沉积Pd膜或Al膜。这些金属膜不仅用作催化剂，而且用作引入射频功率的电极。在LiNbO_3上淀积的40 nm厚的Pd膜上催化乙醇氧化时，在3.4 MHz频率和3 W功率下的共振振荡使乙醛生成量立即增加1900倍，并保持高活性直到关闭电源。非共振频率的应用没有引起显著的活性增强。断电时反应的活化能为156 kJ mol/L<-1>，而通电时活化能急剧下降至12 kJ mol/L<-1>。对于使用催化惰性Al薄膜的样品，观察到催化活性几乎没有增加。表面电位的测量结果表明，共振频率影响电子在表面的分布，而没有发生变化时，非共振频率施加到催化剂。采用激光多普勒方法测量晶格位移。在此基础上，认为导致催化活性异常增强的共振振荡效应与催化剂表面晶格位移和表面电位的变化有关。

In an attempt to design a heterogeneous catalyst with artificially controllable functions, resonance oscillation phenomena generated on a ferroelectric crystal by applying radio frequency electric power were applied. A poled ferroelectric single crystal of lithium niobate (LiNbO_3) was used as a substrate, on which either Pd film or Al was deposited. These metal films were used not only as a catalyst but as an electrode to introduce rf power. In the catalytic ethanol oxidation on a 40 nm thick Pd film deposited on LiNbO_3, resonance oscillation at a frequency of 3.4 MHz at a power of 3 W caused an immediate increase in acetaldehyde production by a factor of 1900, and the high activity was maintained until the power was turned off. The application of non-resonance frequency caused no significant activity enhancement. The activation energy of the reaction was 156 kJ mol^<-1> with power-off, whereas it decreased dramatically to 12 kJ mol^<-1> with power-on. For a sample using a catalytically inactive Al thin film, little increase in catalytic activity was observed. Surface potential measurements showed that the resonance frequency affected the distribution of electrons at surfaces, whereas no change occurred when non-resonance frequency was applied to the catalyst. A laser Doppler method was employed to measure lattice displacement. On the basis of these results, the effects of resonance oscillation which lead to the anomalous enhancement of catalytic activity are considered to be associated with the lattice displacement of catalyst surface and changes in the surface potential.