Shape-controlled Synthesis Of Pd Nanoparticles And Their Catalytic Hydrogenation Properties

Nanostructured metallic particles have been attracted widely attention owing to their excellent catalytic properties. Metal nanoparticles has the advantages of small size and large surface area, numerous studies have shown that the catalytic properties of metal nanoparticles are strongly affected by both the size and shape of the nanocrystals in a catalyst, in principle, one could control the synthesis conditions to finetune the properties of the nanoparticles. Palladium is used as the primary catalyst for its remarkable capacity for hydrogen absorption. Since the facets exposed on a nanocrystal are determined by its shape, in order to further improve the catalytic properties, a large effort has been devoted to the synthesis of monodisperse palladium nanocrystals. Palladium nanoparticles with monodispersive sizes and well-defined morphologies have been obtained by various methods. In this paper, shape-controlled synthesis of the morphological palladium nanoparticles were investigated and applied to the hydrogenation1,4-butyne diol and nitrobenzene.Uniform palladium nanocrystals with cubic shapes were synthesized through a solution-phase method with PdCl2as a precursor, ascorbic acid as a reducing agent and poly(vinyl pyrrolidone)(PVP) serving as a stabilizer. Through the TEM images, we can found that Brcan be used as a capping to selectively promote the formation of{100} facets. The concentration of PVP can change the size of Pd nanoparticles, but will not change the shape of palladium nanoparticles in the present of KBr. Uniform palladium nanocrystals with icosahedron shapes were synthesized through a solution-phase method with Na2PdCl4as a precursor, ascorbic acid as a reducing agent, P123serving as a stabilizer. P123can selectively adsorption on the{111} face and eventually leading to the formation of Pd icosahedrons. Different from P123, PVP shows no selective adsorption between{100} and{111} faces.Uniform palladium nanocrystals with cubic shapes were used as seeds to synthesis nanocubes with large size and polyhedral palladium nanoparticles with different proportions of{100} to{111} facets on the surface. The morphology of the resultant palladium nanocrystals could be conveniently controlled by varying the volume of seed solution while the amount of the PdCl2precursor was fixed. The selective hydrogenation of butyne-1,4-diol was chosen as a model reaction, it was found that the catalytic properties of palladium nanoparticles are mainly determined by its size, shape, composition and structure. All of the palladium nanocrystals showed higher selectivity to2-butene-1,4-diol, and the palladium nanocubes with slight truncation at the corners become the best choice of catalyst for selective hydrogenation of2-Butyne-1,4-diol to2-butene-1,4-diol.Different shapes of palladium nanocrystals were prepared by chemical reduction method and carbon nanotubes after oxidation treatment were used as support to obtained Pd/CNTs catalyst. Palladium nanocrystals with a mix of decanedron and triangle becomes the best choice of catalyst for the hydrogenation of nitrobenzene.