Spatial Confinement Of Highly Dispersed Noble Metal Nanoparticles Within Hollow Thermally Crosslinked Polypyrrole Shell Towards Efficient Heterogeneous Catalysts

The development of high activity and high stability catalysts is of great significance to chemical production.The immobilization of precious metals on supports to synthesize immobilized noble metal nanocatalysts can increase the stability of noble metal nanoparticles.The hollow structure carrier not only facilitates the exposure of the active sites,but also the diffusion of the reactants in the cavity greatly reduces the mass transfer resistance and improves the reaction efficiency of the catalyst.Therefore,this dissertation designs and synthesizes hollow thermally cross-linked polypyrroles with space-constrained noble metal nanocatalysts.Precious metal nanoparticles are dispersed in the hollow shell structure,which can effectively avoid the phenomenon of agglomeration of noble metal nanoparticles.At the same time,the internal cavity of the hollow structure can also provide a bidirectional diffusion mechanism to improve the catalytic activity of the noble metal nanoparticles.The hollow polypyrrole/platinum precursor was firstly synthesized by redox reaction between pyrrole monomer and K₂PtCl₆,and then converted to the hollow thermally crosslinked polypyrrole/platinum nanocatalsyt through H₂ pyrolysis.The platinum nanoparticles with small size are highly dispersed into the thermally crosslinked polypyrrole structure,which improves the utilization efficiency of the precious metal atoms.The thermally crosslinked polypyrrole structure suppresses the migration and agglomeration of small platinum nanoparticles in the catalytic process and enhances their structural stability.As expected,the hollow thermally crosslinked polypyrrole/platinum nanocatalsyt exhibits high activity and robust durability.Secondly,the core-shell Fe₃O₄@PPy/Pt nanocomposites were first synthesized by the redox reaction of pyrrole monomer and K₂PtCl₄,and then magnetic hollow TC PPy/Fe/FePt nanocomposite catalysts were synthesized by pyrolysis of reducing atmosphere.The reaction substrate can be transported in both directions inside and outside the hollow structure cavity to improve the collision probability between the reaction substrate and the catalytic active center.The precious metal Pt exists in the polymer shell structure in the form of FePt alloy,not only can increase the precious metal's Dispersion and stability,Moreover,the reduced Fe nanoparticles enable the magnetic recovery of the catalyst,greatly improving the recycling efficiency of the catalyst.The hollow TC PPy/Fe/FePt nanocomposite catalyst was used for the hydrogenation of nitro groups,showing high catalytic activity and cycling stability.