Penner Simon, Wang Di, Jenewein Bernd, Gabasch Harald, Klötzer Bernhard, Knop-Gericke Axel, Schlögl Robert, Hayek Konrad
Institute of Physical Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria.
J Chem Phys. 2006 Sep 7;125(9):094703. doi: 10.1063/1.2338028.
The formation, thermal decomposition, and reduction of small PdO particles were studied by high-resolution transmission electron microscopy and selected area electron diffraction. Well-defined Pd particles (mean size of 5-7 nm) were grown epitaxially on NaCl (001) surfaces and subsequently covered by a layer of amorphous SiO2 (25 nm), prepared by reactive deposition of SiO in 10(-2) Pa O2. The resulting films were exposed to molecular O2 in the temperature range of 373-673 K, and the growth of PdO was studied. The formation of a PdO phase starts at 623 K and is almost completed at 673 K. The high-resolution experiments suggest a topotactic growth of PdO crystallites on top of the original Pd particles. Subsequent reaction of the PdO in 10 mbar CO for 15 min and thermal decomposition in 1 bar He for 1 h were also investigated in the temperature range from 373 to 573 K. Reductive treatments in CO up to 493 K do not cause a significant change in the PdO structure. The reduction of PdO starts at 503 K and is completed at 523 K. In contrast, PdO decomposes in 1 bar He at around 573 K. The mechanism of PdO growth and decay is discussed and compared to results of previous studies on other metals, e.g., on rhodium.
通过高分辨率透射电子显微镜和选区电子衍射研究了小尺寸PdO颗粒的形成、热分解和还原过程。在NaCl(001)表面外延生长出尺寸明确的Pd颗粒(平均尺寸为5-7nm)，随后用一层非晶态SiO2(25nm)覆盖，该SiO2层是通过在10(-2)Pa O2中反应沉积SiO制备的。将所得薄膜在373-673K的温度范围内暴露于分子O2中，研究PdO的生长情况。PdO相的形成在623K开始，在673K时几乎完成。高分辨率实验表明，PdO微晶在原始Pd颗粒顶部进行拓扑生长。还研究了在373至573K的温度范围内，PdO在10mbar CO中反应15分钟以及在1bar He中热分解1小时的后续反应。在高达493K的CO中进行还原处理不会导致PdO结构发生显著变化。PdO的还原在503K开始，在523K完成。相比之下，PdO在1bar He中于约573K分解。讨论了PdO生长和衰减的机制，并与先前对其他金属(如铑)的研究结果进行了比较。
