Study of Interface and Catalytic Activity on Core-Shell Structured Noble Metal Alloy Nanoparticles

采用超声还原法制备了金核钯壳结构的纳米粒子。颗粒的直径约为4 × 12 nm。核壳结构的AuPd纳米粒子对4-戊烯酸的催化还原具有很高的活性。为了阐明这些纳米颗粒的电子结构，我们测量了^<197>Au穆斯堡尔谱，EXAFS，正电子湮没和高分辨率透射电子显微镜（TEM）。在对Au的<197>穆斯堡尔谱研究中，发现该谱包含两个分量，一个是纯Au的分量，另一个是AuPd合金的分量。从这些组分的面积比可以看出，在Au核和Pd壳之间存在AuPd合金层，合金层的厚度约为3个原子层。Pd-K边的EXAFS结果表明存在Au-Pd合金层。通过XAFS测量观察到Pd壳层上原子间距的扩大。通过正电子湮没符合多普勒展宽测量（CDB），观察了纳米粒子表面的电子态。为了通过TEM观察纳米颗粒的横截面，我们使用超薄切片机并开发了TEM观察的条件。

We prepared the Au-core and Pd-shell structured nanoparticles by the ultrasonic reduction technique. The diameters of the particles are about 4〜12 nm. On the core-shell structured AuPd nanoparticles, there is the high catalytic activity on hydrogenate of 4-penteonic acid. To elucidate the electronic structure of these nanoparticles, we measured ^<197>Au Mossbauer spectroscopy, EXAFS, positron annihilation and high-resolution transmission electron microscope (TEM). On ^<197>Au Mossbauer study, the spectra contain two components, one, is component due to the pure Au, and the other is due to the AuPd alloy. From the area ratio of these components, it is shown that there is the AuPd alloy layer between Au-core and Pd-shell and the thickness of the alloy layer is about 3 atom layers. The result of EXAFS on Pd K edge shows existence of the AuPd alloy layer. The expansion of the atomic distance on the Pd shell is observed by the XAFS measurements. By the positron annihilation coincidence Doppler broadening measurement (CDB), the electronic state of the surface of the nanoparticles are observed. To observe the cross section of the nanoparticles by TEM, we used the ultra microtome and developed the conditions for TEM observation.