Ultrafine Metal Nanocrystals,Metal Clusters:Synthesis And Their Catalytic Properties

With the development of controllable synthesis of metal nano-materials,a large number of metal nanocrystals with controllable components,size,morphologies and exposure crystal plains have been reported,thus applying the nano-synthesis technique to the research of catalytic chemistry has become one of the most available approach in this field.On the other hand,the research methods in homogeneous catalysis based on single center of complexes became mature.The sub-nanometer scale,as the connection of atomic scale and nanoscale,homogeneous catalysis and heterogeneous catalysis,provides a new thought to explore the nature of the catalytic process and develop high efficient catalyst.By means of liquid phase synthesis method and template method,this dissertation explores the synthetic strategies,forming mechanism and catalytic properties of ultrafine metal nanocrystals and metal clusters.Bimetallic catalyst has received wide attention,for its special electronic structure and chemical properties compared to single metal catalyst.In the first part of this dissertation,a modified "liquid-solid-solution" hydrothermal synthesis method was developed to prepare a series of ultra-fine bimetallic nanocrystals.The oxygen reduction reaction catalytic activity of PtCu bimetallic nanocrystals exhibits an evident size dependency.This method is a quite general strategy to prepare ultrafine bimetallic nanocrystals.Highly branched structures show advantages in porous structure,exposure of high index surface and easiness of recycling.In the second part of this dissertation,bimetallic Pt-Ni highly-branched nanocrystals were obtained by a one-pot strategy.The dendritic alloyed structure of the as-prepared nanoparticles was fully characterized and their formation mechanism was investigated.Nitrobenzene hydrogenation reactions indicated that these obtained Pt-Ni nanodendrites exhibited enhanced catalytic activities compared with Pt-Ni nanoparticles.Metal organic frameworks possess large specific surface,novel topological structure and tailored composition,so they can serve as a new kind of supporter.In the last part of this dissertation,metal precursors were introduced into the MOFs by a double-solvent-controlled method.Adjusting the reduction temperature of hydrogen,Ru,Rh,Pt clusters were obtained within the pores of MOFs.We also found that Ru clustershad a good high temperature stability,and performed well in ammonia synthesis.Besides,by introducing MgO to the pores of MOFs,the catalytic activities of Ru clusters could be further enhanced.