Study On The Perparation Of Supported Palladium Nanoparticles Catalysts With Different Morphologies And Their Catalytic Impact On Suzuki Coupling Reaction

Supported palladium catalyst is used to catalyze carbon-carbon coupling reaction that is one of important reactions in the modern synthesis and it is widely used in the synthesis of various compounds. Similar coupling reactions include the Stille coupling reaction, Heck coupling reaction and Suzuki coupling reaction etc. Suzuki coupling reaction has become the most direct and effective method, which can synthase biphenyl compounds. This reaction were catalyzed by palladium catalyst contained various ligands in organic solvents. Suzuki coupling reaction has many advantages in industrial production such as simple operation, widely accessible raw materials and high yield. But carbon-carbon coupling reaction catalyzed by efficient palladium catalyst is a single method of synthesis, there are many disadvantages for example expensive raw materials, difficult recycled catalyst and low yield. Hot spot in recent years is the study of high activity and high selectivity of palladium catalyst application in petrochemical industry. Suzuki reaction is mainly applied to the pharmaceutical production, the synthesis of functional polymer materials and liquid crystal materials. Most of the research reported that Suzuki reaction Usually use aryl bromides, aryliodides or arylchlorides in synthesis process. Homogeneous catalysts were most of ligand-palladium catalysts at this stage, but they were difficult to recycle and reuse after the reaction and also can waste metal palladium, pollute environment especially the water pollution, cause increased costs. So designing a supported palladium catalyst of recycle is the main research direction of Suzuki coupling reaction in recent years. The catalytic activity of nanoparticles is affected by size since the relative ratio of surface atom types(vertex, edge, facets atoms)which changes dramatically with various particle sizes. In many cases, the activity increases as the particle size decreases, it lead to favorable changes in the electronic properties of surface atoms which are mainly located on edges and corners in small particles. So it has attracted great attention.Catalytic studies have shown that the activity of metal nanoparticles can be affected by shape and size of the nanoparticle. Palladium nanoparticles with different morphologies show different selectivity and activity in catalyzing C-C coupling reaction. Vehicle type has obvious influence on the performance of catalyst because of its different structure and properties. In terms of its, the carrier with connected pore structure is beneficial to mass transfer; it has large porosity and specific surface area which provided enough load and the mass transfer area by introducing functional groups activated with metal forming strong chemical bonds.In this paper, TiO2 supported palladium nanoparticles with different morphologies and Pa nanoparticles were characterized by TEM, XRD and XPS. The reaction temperature and time can be determined by comparing the products yields obtained by Suzuki coupling reaction between m-bromotoluene and benzene boric acid.The pompon Pd nanoparticles have been successfully prepared at room temperature for 5 minutes with PVP as protectant, PdCl2 as the source of palladium, NaBH4 as a reducing agent and benzylalcohol as solvent. The Spheriod Pd nanoparticles can be prepared in similar method by adjusting temperature and time, but ammonium formate as the reducing agent, secondary distilled water as the solvent. Also icosahedron palladium nanoparticles can be obtained with glycol as the reducing agent and ethanol as the solvent. And the palladium nanoparticles were characterized by TEM, XRD and XPS, the results show its morphology, particle size. Also we can find that the size of pompon Pd nanoparticles were biggest which were self-assembly.TiO2 supported Pd nanoparticles were prepared by joining titanium dioxide solid to the palladium solution stirring at room temperature for 24 h which ensure its fully adsorption of palladium nanoparticles. Mixed solution dried under in vacuum at 25 �C via rotary evaporator,the obtained TiO2 supported Pd catalysts dried under in vacuum at room temperature. They were characterized by TEM, XRD, results show that the TiO2 has supported palladium nanoparticles and morphology of palladium nanoparticles has changed due to the loss of solvent and affection of temperature in the process, it tend to be isotropic. Using inductively coupled plasma emission spectrometry(ICP) to test the amount of palladium supported on TiO2, the result show that palladium content of TiO2 supported Pd nanospheres is the largest.Biphenyl compounds were prepared by the Suzuki reaction between m-bromotoluene and benzene boric acid with potassium carbonate as alkaline reagents, TiO2 supported Pd as catalyst, DMF solution(DMF: H2 O = 1:1) as solvent under certain temperature and time. The reaction temperature and time can be determined by comparing the products yield. The best temperature of reaction catalyzed by supported icosahedron Pd nanoparticles was 110 ? and time was 2 h.