Preparation Of Carbon Loaded Nano Pd Catalysts And The Study Of Catalytic Coupling Reactions

Pd-catalyzed coupling reaction (Heck reaction, Suzuki reaction) is one of the most important methods to connect the C-C bond in modern organic synthesis, which have wide application prospects. Palladium has excellent catalytic activity, but it is limited in industry because of high cost and difficult recovering. A heterogeneous palladium catalyst is a good solution to this problem. However, the reaction activity is low for the chlorobenzene and bromobenzene using loaded type Pd-catalyzed, normally it is suggested to add organic phosphorus ligand which is toxic and hard to prepare to improve their catalytic activity. Therefore, it’s significant to design a nano-palladium catalyst that has no phosphorus ligand, is easy for preparation, has high catalytic activity, and can be reused for catalyzed coupling reaction.In this paper, coconut shell activated carbon is chosen as a carrier that has the account of3100-3200m2· g-1high specific surface area sodium citrate is used as a reducing agent. After a mixture of both sonication, adding distilled water and bring to boil, and adding the acide solution of palladium chloride to restore load preparation respectively, six type of nano Pd/C catalysts have been created. Their particle size are3-20nm, particle dize distribution is nattor and controllable. Using transmission electron microscopy (TEM) and X-ray diffraction (XRD) to characterized the6different types of Pd particle size of Pd/C catalysits, it is aim to find the principle of macro-controlling the Pd particle diameter. This preparation method is simple and within mild conditions, the particle size of Pd can be controlled by amending the amount of sodium citrate and H2PdCl4solution, and therefore it can be achieved an even particle distribution with less agglomeration.The optimal reaction condition was studied for the Heck and Suzuki coupling reaction. From the report it can be seen that, the nano-Pd/C catalyst has excellent catalytic activity in coupling reaction of halogenated aromatics in the air and under no phosphorus ligand conditions. Especially it can make aryl chlorides react which is difficult to make the coupling reaction. It is also found that the smaller particle size, the higher catalytic activity; the greater volume of catalyst, the higher catalytic activity.It is obtained a series of stilbene and biphenyl compounds through coupling reaction, and their structures are also characterized by NMR and IR. The result shows that, if the ortho positon is connected to a substituent, the reaction will be suppressed, versus if the meta-position is in connected to a substituent. If substituent is connected to the same position, the product yield of connecting electron withdrawing groups is higher than connecting electron donating group.In addition, the repeat performance of nano Pd/C catalyst was focused during catalyzed Heck Reaction and Suzuki Reaction in this paper. It can be recycled after simple filtration and washing; can be reused after8times with a70%and84%product yield to catalyzed Heck and Suzuki reaction. The electron micrograph shows that, after catalyst being repeated use, the surface state has been changed, the activity has been reduced due to the fact that the Pd particles become large and agglomeration. It is also proved that this heterogeneous catalyst is involved in catalytic reaction with a homogeneous state.