Design And Synthesis Of Pd-based Metallic Nanoparticles With High Dispersion,High Stability And High Activity

Metal nanoparticles possessed specific thermal,electronic,magnetic and optical performances,have attracted tremendous attentions in the field of energy,environmental protection,petrochemical engineering,biomedical and so on.All these specific performances are based on their small size.However,due to their high surface energy,the aggregation usually occurs with metal nanoparticles,resulting in losing the specific performances they owned.Therefore,it is crucial to prevent metal nanoparticles from aggregation.One effective approach to stabilize metal nanoparticles is to enhance the repulsive force between each metal nanoparticle by using stabilizers.Polymer is one of the most common and useful stabilizers.However,compared with polymer,inorganic material has some irreplaceable advantages for stabilizing metal nanoparticles,such as,high thermal stability and chemical stability.For catalytic applications,there have even more advantages for metal nanoparticles stabilized by porous materials.Porous materials with the advantages of uniform pore size,high surface area and high thermal stability,would be well used to enhance the activity and stability of metal nanoparticles and facile the diffusion rates of the reactants and the products in catalytic reactions.In this thesis,by using porous materials with different mesostructures,porosities,and compositions as supports,we realize the synthesis of metal nanoparticles with high dispersion,high stability and high activity.More details are shown as follows:Firstly,development of a facile high-viscosity-solvent method for synthesizing highly dispersed metal nanoparticles.We choose 2D mesoporous silica materials as the supports to synthesize PtPd bimetallic nanoparticles.The as-synthesized 2D order mesoporous materials(SBA-15 and MCM-41)have been used as reactor to in suit synthesize PtPd bimetallic nanoparticles with high dispersion by the high-viscosity-solvent method.The formation mechanisms of nanometals in different viscosity solvents have been proposed and proved by analyzing the cases of PtPd bimetallic nanoparticles synthesized in various viscosity solvents.The synthesizedPtPd bimetallic nanoparticles within porous materials exhibit high dispersion.Secondly,structure extension of high-viscosity-solvent method for synthesizing highly dispersed metal nanoparticles.We choose 3D mesoporous silica materials as the supports to synthesize PtPd bimetallic nanoparticles.The as-synthesized mesoporous materials with 3D continuous pore systems(MCF)have been used as reactor to in suit synthesize PtPd bimetallic nanoparticles with a special “one particle@one cell” structure by the high-viscosity-solvent method.The synthesized monodispersed PtPd bimetallic nanoparticles exhibit high catalytic activity,high stability and high durability in hydrogenation of nitrobenzene.Thirdly,application extension of high-viscosity-solvent method for synthesizing highly dispersed metal nanoparticles.We choose mesoporous carbon materials as the supports to synthesize PtPd bimetallic nanoparticles.The as-synthesized mesoporous carbon materials(CMK-3 and MCF-C)have been used as reactor to in suit synthesize PtPd bimetallic nanoparticles with high dispersion by the high-viscosity-solvent method.The synthesized highly dispersed PtPd bimetallic nanoparticles exhibit high catalytic activity,high stability and high durability in oxygen reduction reaction.Finally,stabilization extension of synthesis method for metal nanoparticles.On the basis of the above study,we deeply investigate that the effects of porous shell on the surface of metal nanoparticles on their catalytic activity and stability.The as-synthesized cubic Pd nanoparticles have been covered with a mesoporous silica shell.By controlling the amount of silicon sources,the mesoporous silica shell with different shapes and sizes have been synthesized successfully.The catalytic results indicate the mesoporous silica shell would retain the catalytic activity of metal core and greatly enhance their reusability.Our investigations demonstrate that high dispersion of metal nanoparticles could result in their high stability,which would further lead to their high catalytic activity.High dispersed metal nanoparticles stabilized by mesoporous materials could enhance the catalytic activity of metal nanoparticles as well as their stability,which show good potential and investigation value in the field of catalysis.This thesis includes six chapters.In Chapter 1,we introduce the developments,classifications and applications of the stabilization of metal nanoparticles.In Chapter2,we investigate 2D mesoporous silica materials stabilized metal nanoparticles.InChapter 3,we investigate 3D mesoporous silica materials stabilized metal nanoparticles.In Chapter 4,we investigate mesoporous carbon materials stabilized metal nanoparticles.In Chapter 5,we investigate the metal nanoparticles core encapsulated by shape-controlled mesoporous silica shell.In Chapter 6,we conclude the above mentioned investigations on stabilization of metal nanoparticles and outlook on further development of our work.