Controllable Preparation And Catalytic Performance Of PS/Pd, PS/Au-Pd And PS/RGO@Pd Composite Particles

Supported palladium?Pd? nanoparticles have attracted huge attention of scientific and industrial community due to their high catalytic activity in various liquid phase chemical reactions. Meanwhile, the existence of support materials makes it more convenient for the recycling of Pd nanoparticles, thus improving the reusing persistence and efficiency of Pd nanoparticles. On the other hand, it is of great importance to further improve the catalytic performance of supported Pd nano-catalysts in their practical application. For example, alloying Pd nanoparticles with another metal and combining them with functional components are two typical methods. For this purpose, this thesis mainly focuses on the simple and controllable preparation of supported Pd nanoparticles and the improvement of their catalytic performance.?1? Controllable preparation and catalytic performance of polystyrene/palladium?PS/Pd? composite particlesOn the basic theory of colloidal stability, the Pd nanoparticles were deposited onto the surface of the PS microspheres to form PS/Pd composite particles with the aid of thermodynamic effect in the colloid system. Specifically, palladium chloride?Pd Cl₂? and trisodium citrate?Na₃Ct? were used as precursor and stabilizer, respectively. Hydrophilic Pd nanoparticles were prepared by chemical reaction and the size of Pd nanoparticles could be controlled by changing the molar ratio of reducing agent, stabilizer and precursor. Subsequently, Na₃Ct-stabilized Pd nanoparticles and hydrophobic PS microspheres were mixed in the water, which the former would assemble onto the surface of the latter based on the minimization principle of Gibbs free energy. Different from the existing methods of preparing the supported Pd nanoparticles, the method in this chapter was simple and controllable. Finally, catalytic research showed that the prepared PS/Pd could catalyze the reduction of p-nitrophonol?4-NP? to aminophenol?4-AP? with high activity and good stability.?2? Controllable preparation and catalytic performance of polystyrene/gold-palladium?PS/Au-Pd? composite particles.Compared to Pd nanoparticles, the Au-Pd alloy nanoparticles tend to exhibit more excellent performance in catalytic application. Similar to the preparation of PS/Pd, Au-Pd alloy nanoparticles were immobilized on the PS microspheres based on the minimization principle of Gibbs free energy. Specifically, using chloroauric acid?HAuCl4? and PdCl₂ as precursors, Na₃ Ct as stabilizer, respectively, hydrophilic Au-Pd nanoparticles were obtained by chemical reaction in water. Besides, the Au-Pd alloy nanoparticles with similar surface properties but different metal elementary composition could be obtained by simply changing the molar ratio of the two precursors. Finally, the catalytic study indicated that the supported Au-Pd alloy nanoparticles exhibit higher catalytic activity than monometallic Au or Pd. Meanwhile, the catalytic performance of PS/Au-Pd has an apogee when the molar ratio of two metal is nearly 1:1. Significantly, Au-Pd alloy nanoparticles could be easily recycled with remaining higher catalytic activity due to the existance of PS microspheres.?3? Controllable preparation and catalytic performance of polystyrene/reduced graphene oxide@palladium?PS/RGO@Pd? composite particlesA simple and controllable strategy was designed to prepare PS/RGO@Pd composite particles. First, by the means of hydrophobic interaction and ? electron interaction, the RGO could be deposited onto the surface of PS microspheres which prepared by dispersion copolymerization method and acted as seeds to form PS/RGO composite particles. Subsequently, the PS/RGO was mixed with PdCl₂ solution to prepare PS/RGO@Pd composite particles. Due to the difference of reduction potential between RGO and PdCl₂, Pd2+ was in situ reduced and deposited on the surface of PS/RGO. In the above process, the size of Pd nanoparticles supported on PS/RGO could be controlled easily by changing the dosage of PdCl₂. More notably, no surface pretreatment of PS microspheres and PS/RGO is required and neither additional stabilizer nor reducing agent is needed during the formation and stabilization of Pd nanoparticles. Compared to the PS/Pd composite particles, the PS/RGO@Pd composite particles showed higher catalytic performance towards the reduction of 4-NP. This mainly attributed to the existence of RGO and the clean surface of Pd nanoparticles. Moreover, the results confirmed PS/RGO@Pd possessed high catalytic activity when being applied to Suzuki coupling reaction.