Department of Chemical Engineering and Materials Science, University of California-Davis, One Shields Avenue, Davis, California 95616, USA.
ACS Nano. 2009 Nov 24;3(11):3691-5. doi: 10.1021/nn9008142.
Highly dispersed supported gold offers unprecedented catalytic properties. Determination of the dependence of the catalytic properties on the gold nanocluster size requires the preparation of size-controlled gold nanoclusters on support surfaces with a high degree of uniformity. Starting from site-isolated mononuclear gold complexes on high-area MgO, we demonstrate the preparation of gold clusters consisting of <10 atoms. These samples have been imaged with atomic resolution by aberration-corrected scanning transmission electron microscopy. The images show that treatment of the supported mononuclear complexes at 318 K in flowing helium caused aggregation of the gold into clusters of 2-6 atoms, present with unconverted individual site-isolated mononuclear gold species and in the absence of any larger nanoparticles. Treatment of the sample at a higher temperature (373 K) in flowing helium resulted in the formation of gold clusters with diameters of 0.58 +/- 0.15 nm (containing roughly 10 Au atoms), again in the absence of larger nanoparticles. Upon exposure of the supported nanoclusters to the electron beam, they underwent aggregation to gold clusters approximately 1 nm in average diameter, as shown in consecutive STEM images.
高度分散的负载金提供了前所未有的催化性能。确定催化性能对金纳米团簇尺寸的依赖性，需要在具有高度均匀性的支撑表面上制备尺寸可控的金纳米团簇。我们从高面积 MgO 上的孤立单核金配合物出发，证明了可以制备由 <10 个原子组成的金团簇。这些样品已经通过具有像差校正的扫描透射电子显微镜以原子分辨率成像。这些图像表明，在氦气流中于 318 K 下处理负载的单核配合物会导致金聚集形成 2-6 个原子的团簇，同时存在未转化的单个孤立单核金物种，并且没有任何更大的纳米颗粒。在氦气流中于更高温度（373 K）下处理样品会导致形成直径为 0.58 +/- 0.15 nm 的金团簇（包含大约 10 个 Au 原子），同样没有更大的纳米颗粒。在将负载的纳米团簇暴露于电子束下时，它们会聚集形成平均直径约为 1nm 的金团簇，如连续的 STEM 图像所示。
