Preparation And Catalytic Properties Of MOFs Supported Noble Metal Nanoparticles

Noble metal nanoparticles-based composite materials have important research significance in the field of catalysis.It can not only reduce the possibility of aggregation of noble metal nanoparticles due to small size,high surface energy and strong van der Waals force between particles,but also facilitate effective recovery and reuse of noble metal nanoparticles.Thanks to the ultra-high specific surface area,adjustable pore structure and diversified composition of metal organic frameworks?MOFs?,combining MOFs with noble metal nanoparticles has become a research hotspot,which can effectively improve the catalytic activity and stability of noble metal nanoparticles.Based on this,two simple and controllable preparation methods were developed to simplify the preparation process of composite materials and improve the catalytic activity and stability of composite materials in this paper.Two kinds of MOFs/noble metal nanoparticles composites with different structures were obtained successfully,and their catalytic performance were studied.Specific research contents are as follows:?1?In this paper,by improving the traditional"double solvent method",a simple and controllable preparation method was developed,which can successfully form a complete shell of palladium nanoparticles@polypyrrole?Pd@PPy?nanocomposite on the surface of UiO-66particles.The specific preparation process is as follows.First,the aqueous solution of PdCl₂was added to the n-hexane dispersion of UiO-66 particles with hydrophilic channels,and the aqueous solution of the PdCl₂ would spontaneously enter the pores of UiO-66 particle.Second,after adding hydrophobic pyrrole into the above dispersion,the chemical oxidative polymerization between PdCl₂ and pyrrole would be initiated on the interface between UiO-66 particles and n-hexane,resulting in the formation of nanocomposite of Pd@PPy,which was named UiO-66/Pd@PPy nanocomposite particles.It was worth noting that there was no need to do specific surface modification or functionalization of the UiO-66 during the synthetic process.By using pyrrole as a reductant of PdCl₂,Pd nanoparticles were formed on the surface of UiO-66 particles and a layer of PPy was obtained to further improve the function of Pd nanoparticles through one-step chemical redox reaction.Besides,the strategy was universal and a series of noble metal nanoparticles@conducting polymer coated UiO-66particles were prepared with different conducting polymer monomers and noble metal precursors.Finally,the prepared UiO-66/Pd@PPy nanocomposite particles were demonstrated to be an excellent catalyst with both high activity and stability in the reduction reaction of p-nitrophenol and NaBH₄.?2?In this paper,sacrificial template method was used and polyvinyl pyrrolidone?PVP?-stabilized polystyrene?PS?microspheres were chosen as template to fabricate reverse bumpy ball-type Pd@ZIF-8 microspheres,in which Pd nanoparticles were encapsulated on the internal surface of ZIF-8 shell.PS microspheres acted not only as templates to obtain the cavity after being removal,but also as carriers of Pd nanoparticles and ZIF-8 shell.The ingenious selection of PVP as the stabilizer of PS microspheres could effectively simplify the preparation process of this hierarchical hollow structure.Specifically,PVP herein could not only function as the reductant and stabilizer for the in-situ generation of palladium nanoparticles?Pd NPs?on the surface of template microspheres,but also provide coordination interaction with zinc atoms in ZIF-8 nodes for the preferentially nucleation and growth of uniform ZIF-8 shell on the surface of PS microspheres.In other words,the deposition of Pd nanoparticles and ZIF-8 shell could be achieved without any specific surface treatment of the template microspheres in the preparation process.Furthermore,while the preparation process was simplified,the method proposed in this chapter had certain controllability and universality.The structure and morphology of ZIF-8 shell could be effectively regulated by changing the concentration of zinc nitrate.And different noble metal precursor solutions,such as silver ammonia solution,could be used to obtain Ag@ZIF-8 hollow microspheres.In the end,the Pd@ZIF-8 hollow microspheres were confirmed to exhibit remarkable catalytic activity,molecular size selectivity with substrates and recyclability in the liquid-phase hydrogenation of olefins.