Synthesis Of Core-shell Nanocatalysts Of Noble Metal Capped By SiO₂ And Their Application

Nanocatalysts,especially sub-10 nm nanocatalysts,tend to agglomerate and sinter at moderate-to-high temperature,which decreases their activity.Core–shell structures,one kind of material coated by another,can effectively separate the core particles,thus protect the particles from agglomeration,and these two materials may bring unique collective and synergetic catalytic properties.This thesis studied a method to synthesize Ru@H-SiO₂ nanoparticles,and their catalytic activity for synthesis of ammonia.The Ru@SiO₂ NPs were firstly prepared via a reverse microemulsion method.After calcination and reduction,the author ultimately obtained single-cored Ru@H-SiO₂ core-shell nanoparticles with around 4.3 nm Ru cores and hollow SiO₂ shells,and this structure showed promising sintering resistance at 500 ?.Unfortunately,the Ru@H-SiO₂ nanoparticles had bad performance at catalyzing for synthesis of ammonia.This thesis studied different method to synthesize Ru@H-ZrO₂?Ru?SiO₂?Au-Fe3O4@SiO₂ nanoparticles.Ru@H-ZrO₂ core-shell nanoparticles with Ru cores and hollow ZrO₂ shells,showed high catalytic activity for synthesis of ammonia.Ru?SiO₂ nanoparticles with needlelike Ru cores and hollow rodlike SiO₂ shells,showed excellent catalytic activity for synthesis of ammonia.Au-Fe3O4@SiO₂ had core-shell structure with dumbbell Au-Fe3O4 cores and SiO₂ shell.