Synthesis And Catalytic Properties Of Palladium Nanoclusters At Atomic-Scale Level

Noble metals are world wide welcome as jewelry and currency due to their expensive price and stable physical and chemical properties. Scientists have found that compared to other precious metals, palladium has high stability and excellent catalytic effect, so it can be used to catalyze many organic reactions. More importantly, with the improvement of synthetic methods and the development of single-crystal diffraction techniques, Scientists synthesized a variety of precise atomic palladium clusters, which provides a strong guarantee for palladium clusters in catalysis. Compared to conventional metal nanoparticles, the accurate structure of precise atomic metal clusters can help us to explore the relationship between structure and properties of the catalyst. In this article, we synthesized monodispersed alloy and precise atomic palladium clusters based on some previous studies, and catalyzed in organic reactions:investigating the catalytic activity and reaction mechanism at the atomic level. The main contents are as follows:1. A series of AuPd@C nanoalloy catalysts with tunable compositions were successfully prepared by a co-reduction method. The use of borane-tert-butylamine complex as reductant and oleylamine as both solvent and reductant was very effective for the preparation of the monodispersed nanoalloy. We evaluated the catalytic activity of these AuPd@C nanoalloys for oxidative dehydrogenative coupling of aniline, which showed better catalytic activity than equal amounts of sole Au@C or Pd@C catalyst. The Au1Pd3@C catalyst exhibited the best performance, indicating that the conversion and selectivity were improved along with the increase of Pd composition. However if the Pd composition was too high in the AuPd alloy, Au1Pd7@C achieved only 81% conversion in this reaction.2. Palladium-catalyzed Suzuki-Miyaura coupling reaction is one of the most versatile and powerful tools for constructing the carbon backbones. It is difficult to explore how the Pd nanoparticles catalyze Suzuki coupling reactions under aerobic conditions owing to their unknowable surface active site, design of atomically precise metal cluster catalysts is of great importance in understanding the essence of the catalytic reactions at the atomic level. Herein, we devised and synthesized a catalyst of single active site-[Pd3Cl(PPh2)2(PPh3)3]+cluster to investigate the catalytic mechanism of a typical Suzuki reaction under aerobic conditions. Our findings explicitly reveal that the accurate intermediate [Pd3Ar(PPh2)2(PPh3)3]+of the catalytic cycle which is evidenced by mass spectrometry, Quick X-ray absorption fine structure and density functional theory calculation analyses. It is proposed that the reaction mechanism catalyzed by Pd clusters is fundamentally different from that of the traditional Suzuki reaction. Our research may provide a new perspective for the catalytic mechanisms of C-C Coupling Reactions catalyzed by metal clusters or nanoparticles.