Exploration Of Catalytic Properties Of Ultrasmall Gold Nanoclusters

Noble metals are world wide welcome as jewelry and currency due to their expensive price and stable chemical properties. In the late20th century, scientists found that the air-stable gold were capable to catalyze a wide range of organic reactions. After2000, the literatures about synthesis and property research of nano gold material have emerged in large numbers. With the help from the progress of new synthetic methods and single crystal diffraction technology, chemists could synthesize and characterize the atomically precise gold nanoclusters, and the investigation and application of nano metal catalysis has been well developed. Materials in nanoscale are quite different from their bulk counterparts in physical and chemical properties, owing to their quantum size effect and enormous surface/volume ratio. In this article, we synthesized three kinds of ultrasmall noble metal nanocluster and applied them in organic catalysis; besides, the catalytic mechanism at atomic and molecular level was also revealed. The main content includes:1. We are inspired to explore gold nanoclusters supported on mesoporous CeO2nanospheres as nanocatalysts for the reduction of nitrobenzene. Ultrasmall Au nanoclusters (NCs) and mesoporous CeO2nanospheres were readily synthesized and well characterized. Due to their ultrasmall size, the as-prepared Au clusters can be easily absorbed into the mesopores of the mesoporous CeO2nanospheres. Owing to the unique mesoporous structure of the CeO2support, Au nanoclusters in the Au@CeO2may effectively prevent the aggregation which usually results in a rapid decay of the catalytic activity. It is notable that the ultrasmall gold nanoclusters possess uniform size distribution and well dispersibility on the mesoporous CeO2supports. Comparing to other catalyst systems with different oxide supports, the as-prepared Au nanocluster-CeO2nanocomposites nanocatalysts showed efficient catalytic performance on transforming nitrobenzene into azoxybenzene. In addition, a plausible mechanism was deeply investigated to explain the transforming process. Au@CeO2performed efficient catalytic activity for nitrobenzene reduction. This strategy may be easily extended to fabricate many other heterogeneous catalysts including ultrasmall metal nanoclusters and mesoporous oxides. 2. Design of atomically precise metal nanocluster catalysts is of great importance in understanding the essence of the catalytic reactions at the atomic level. In this article, Au25z nanoslusters were employed as electron transfer catalysts to induce an intramolecular cascade reaction at ambient conditions and gave rise to high conversion (87%) and selectivity (96%). Electron spin-resonance spectra indeed confirmed the consecutive electron transfer process and the formation of N radical. UV-vis absorption spectra and MALDI TOF MS also verified Au25z was intact after the catalytic circle. Our research may open up wide opportunities for extensive organic reactions catalyzed by Au25z. Atomically precise Au25nanocluster catalysts may offer great opportunities to unravel the correlation between structure and property, and present an easy access to understand the catalytic mechanism at atomic and molecular level. It is the first successful attempt to induce the intramolecular cascade reaction of2-nitrobenzonitrile using AU25-clusters as electron-transfer catalysts from which the single electron is transferred to neutral organic molecule. Moreover, it undertakes a good start for electron-transfer catalysis of AU25clusters in extensive organic reactions.3. A simple and efficient method for the synthesis of ultrasmall Pd nanoclusters (NCs) has been developed. The as-obtained Pd NCs displayed uniform size with an average diameter of1.8±0.2nm. Furthermore, the ultrasmall Pd NCs and carbon nanotubes supported Pd NCs showed outstanding catalytic activity for nitrobenzene reduction and Suzuki coupling reactions. Notably, all the reactions were conducted under mild conditions with high yield and selectivity.