Preparation Of Metal-Based Magnetic Spatial Confinement Nanocatalyst And Their Catalytic Properities

For the chemical industry, it is very important to develop catalysts with high efficiency, high stability and easy recoverability. Metal-based magnetic nanocatalysts have attracted much attention for their high catalytic activity of metal nanoparticle and facile recoverbility of magnetic support. Howere, metal nanoparticles are often supported on the surface of the magnetic support, thus they may suffer from aggregation in catalytic transformations, thereby resulting in a dramatic decrease in their initial activity, possibly owing to their high surface energy. Metal-based magnetic spatial confinement nanocatalyst can confine metal nanoparticles within magnetic supports, and can avoid the aggregation. Hence, this work focus on the design and synthesize of the metal-based magnetic spatial confinement nanocatalyst, which could be easily collected by an external magnetic field, and limit the metal nanoparticles into the structure of the magnetic support to improve the dispersity and stablity of the metal nanoparticles.Firstly, a soft template-assisted simultaneous redox strategy was used to fabricate Fe3O4@polypyrrole/Pd(Fe3O4@PPy/Pd) nanocomposites with core-satellite stucture on the basis of simultaneous redox reduction of pyrrole monomer and H2PdCl4 with amphiphilic polyvinylpyrrolidone(PVP) random coils as soft-templates, in which the Fe3O4 nanocluster was acted as the core and multiple PPy/Pd particles of the size ranges from 20 to 30 nm as the satellites, into each of which multiple tiny Pd nanocrystals are uniformly confined. The dispersion of Pd nanocrystals into PPy satellites and the Pd loading of the nanocatalyst could be finely tuned by tailoring the polarity of the reaction medium and by changing the molar ratio of pyrrole monomer to Pd precursor,respectively. The Pd based catalyst shows high activity, robust stability and magnetic recyclability for the reduction of nitroaromatic compounds. Superior activity could be attributed to the short transport route toward the active Pd nanocrystals within the small PPy satellite for the outer substitutes. Meanwhile, high stability could be ascribed to the confinement of Pd nanocrystals uniformly into PPy satellites against aggregation and even loss of active sites during catalytic transformationsSecondly, a sacrifial templating method was employed to synthesize Fe3O4@Ni3Si2O5(OH)4 nanocomposites with yolk-shell structure under hydrothermal conditions. In the preparation process, Fe3O4@SiO2 microspheres with core-shell structure was used as the template. Fe@SiO2/Ni nanocomposties with yolk-shell were obtained by reduction of Fe3O4@Ni3Si2O5(OH)4 nanocomposites, the Fe3O4 core was reduced to Fe nanoparticles and Ni nanoparticles were in situ generated. Ni nanoparticles were confined into the structure of SiO2 nanosheets, which avoid the migration and aggregation of the Ni nanoparticles and enhance the stability. The catalysts were used in the reduciton of nitroaromatic compounds and exhibited good catalytic activity, high stability and magnetic recyclability.