Study On The Shape-control Synthesis Of Palladium Nanoparticles And Their Catalytic Properties

Palladium nanomaterials play a central role in many industrial applications fortheir unique chemical and physical properties. They can serve as the hydrogen sensorsand hydrogen storage materials as well as excellent electrocatalysts in fuel cells.Moreover, Pd nanoparticles were also widely used as the catalyst for thelow-temperature reduction of automobile pollutants and a range of organic reactionsincluding coupling reactions that include Suzuki, Heck and Stille coupling. It has beenknown that the property of the nanoparticles is strongly dependent on their shapes,size and structures, therefore, many researchers committed their superior performancein the catalyst. Self-assemblies metal nanostructures have attracted much researchattention owing to their various potential applications deriving from their uniqueoptical, electronic, magnetic, catalytic and sensing properties. Essentially, theydemonstrate better recycle performance than those mono-dispersed small primarynanoparticles. So far, the control handles available for the syntheses of palladiumnanostructures have been limited to the reaction temperature, the concentration of Pdprecursor, and the structure of the surfactant or polymer, but the effect of the solventare rarely studied, as well as the self-assembly palladium nanostructures. In this paper,we mainly focus on usig proper solvent and reducing agent to control the shape of Pdnanoparticles, the as-prepared palladium nanoparticles were characterized bytransmission electron microscopy(TEM), X-ray photoelectron spectroscopy(XRD)and X-ray powder diffraction(XPS).Furthermore, the effect of protecting agent PVP,the reaction time, reducing agent, solution and heating method have been discussed.Then the prepared Pd nanoparticles were used as the catalyst of the Suzuki reaction.Self-assembly porous Pd nanospheres have been successfully prepared withNaBH4as reducing agent and benzyl alcohol as solvent in the presence ofpolyvinylpyrrolidone (PVP) at room temperature for5minutes. The as-synthesizedPd nanospheres were characterized by TEM, XRD and XPS. The results show that theas-prepared Pd nanostructures were self-assemblies organized by hundreds of smallerprimary nanoparticles with an average dimension of about6.6nm. The reducing agent,reaction time, solution species, molecular weight of PVP and the molar ratio of benzylalcohol to water can influence the morphology of the Pd nanosphere.Pd nanosphere with a mean size of101.7nm were synthesized by heatingH2PdCl4in the presence of PVP at130℃for5h, the as-prepared Pd nanostructureswere characterized by TEM, XRD and XPS. The influence of the reducing agent,reaction time, solution species, the concentration of PVP, the precursor species, thetemperature, the heating method as well as the molar ratio of benzyl alcohol to Dimethyl Sulfoxide on the shape of Pd nanoparticles have been discussed.The catalytic activities of Pd nanoparticles with different shapes wereinvestigated preliminarily by Suzuki reaction. The results showed that the catalyticactivity of the self-assembly porous Pd nanospheres were organized by hundreds ofsmaller primary nanoparticles shows the best catalytic activities due to their largesurface area and high concentration of coordinatively unsaturated surface atoms.