Preparation And Application Of Noble Metal-Based Nanocomposites

Due to the combination of noble metals and other components,noble metal-based nanocomposites show unique physical and chemical properties in areas such as photocatalysis,pharmaceutical synthesis,environmental catalysis,electrocatalysis and oxidation/combustion reactions.The noble metal-based composite nanomaterials are now mainly obtained by aqueous phase synthesis and organic phase synthesis.Aqueous phase synthesis requires the use of very expensive chemical reagents and low concentrations of precursors,making it difficult to prepare on a large scale.The metal core obtained by organic phase synthesis must occupy a large proportion to avoid excessive deposition of the metal shell on the surface of the core,but the exposed area of the active metal and the active area participating in the catalytic reaction are small,which is not conducive to the catalytic reaction.Therefore,the current research focus is to reduce the amount of noble metals and improve the catalytic performance of unit noble metals.In this paper,the structure of noble metal-based nanocomposites are regulated in order to enhance their electrochemical catalysis and environmental catalytic activity by utilizing the altered electronic structure in the regulation process and the structural advantages of the modified nanomaterials.Based on this overall idea,the paper specifically improves the utilization of noble metal atoms through increasing the atomic dispersion and utilizing the advantages of hollow structures.Firstly,the atom dispersion of noble metals is realized from the point of view of improving the atom dispersion.Specifically,this strategy involves the synthesis of copper(Cu)nanoseeds in oleylamine,the galvanic replacement reaction(GRR)between Cu seeds and palladium(Pd)ions for forming bimetallic Cu-Pd nanoalloys,the deposition of Cu-Pd nanoalloys on y-aluminum oxide(y-Al2O3)substrates,and the subsequent thermal treatment for oxidizing the Cu component in the alloy particles.It corresponds to the fact that Pd alloys are dispersed in copper oxide(CuO)at an atomic level.Then the prepared noble metal-oxide nanocomposites were tested for the catalytic oxidation of benzene.The results showed that the catalytic performance is better when the Pd content is increased.In addition to the influence of Pd content,the activity of benzene catalytic oxidation is also related to the dispersibility of Pd.When the Pd content is decreased,the degree of dispersion is increased,and the agglomeration of Pd atoms can be effectively prevented,thereby increasing the catalytic activity of each active site.At the same time,the catalysts also showed good stability and water vapor resistance performance.The method combines GRR with thermal treatment and saves the amount of noble metals,which make it possible to efficiently utilize noble metal components and improve the catalytic performance.In addition,we utilizes the advantages of hollow structure and investigates the growth mechanism of noble metal-semiconductor composite nanomaterials.The core-shell Ag@Pt nanoparticles were firstly obtained from silver(Ag)nanoseeds and platinum(Pt)ion,and then reacted with different sulfur(S)sources.By observing the TEM images of the products formed during the different structural transformation processes,the formation mechanism of silver sulfide-hollow platinum nanocomposites(Ag2S-hPtNCs)was proposed.Then the catalyst was applied to the methanol oxidation reaction(MOR).Due to the strong electron coupling between Ag2S and hPt in the Ag2S-hPtNCs/C nanocomposites,Ag2S-hPtNCs/C showed excellent MOR performance under acidic conditions.The electron coupling effect in the composite is due to the charge transfer between the noble metal and the semiconductor.The change of the electronic structure can effectively adjust the density of the d-orbital density center of the noble metal and the electron cloud density of the surface atom,which could better balance the adsorption of reactants and intermediates on the surface of the noble metal atoms during MOR and reduce CO poisoning,thereby exhibiting the best catalytic performance.