Department of Chemistry, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Phys Chem Chem Phys. 2012 Feb 21;14(7):2152-8. doi: 10.1039/c1cp22466b. Epub 2011 Oct 13.
Formation and oxidation processes of PdZn nanoparticles on ZnO were successfully observed by means of in situ time-resolved X-ray absorption fine structure spectroscopy (XAFS), and the analysis of data on near-edge (XANES) and extended (EXAFS) structures revealed detailed changes in Pd during both processes. PdZn nanoparticles were formed on ZnO through a two-step scheme under a hydrogen atmosphere. The first process was the formation of metallic Pd nanoparticles, which was quickly finished within 1 s. The second process was the formation of PdZn nanoparticles, which took several tens of minutes. Oxidation of the PdZn nanoparticles also consisted of two processes. Zn atoms were oxidized prior to Pd atoms and the metallic Pd nanoparticles surrounded by ZnO were formed afterwards. Oxidation of the metallic Pd nanoparticles was scarce and very slow. According to the results of kinetic analyses, the metallic Pd surrounded by ZnO was a stable species under the oxidative atmosphere.
采用原位时间分辨 X 射线吸收精细结构光谱（XAFS）成功观察了 ZnO 上 PdZn 纳米粒子的形成和氧化过程，对近边（XANES）和扩展（EXAFS）结构的数据进行分析揭示了 Pd 在这两个过程中的详细变化。在氢气气氛下，PdZn 纳米粒子通过两步方案在 ZnO 上形成。第一过程是形成金属 Pd 纳米粒子，该过程在 1 秒内迅速完成。第二过程是 PdZn 纳米粒子的形成，这需要几十分钟。PdZn 纳米粒子的氧化也包括两个过程。Zn 原子先于 Pd 原子被氧化，随后形成被 ZnO 包围的金属 Pd 纳米粒子。金属 Pd 纳米粒子的氧化很少且非常缓慢。根据动力学分析的结果，在氧化气氛下，被 ZnO 包围的金属 Pd 是一种稳定的物质。
