Study On The Synthesis And Reactive Properties Of Supported Au Yolk-Shell Nanocatalysts

Due to their excellent catalytic activity and selectivity,supported Au nanocatalysts have been extensively and deeply researched in important chemical reactions in the catalysis fields.Dispersing ultrafine Au nanoparticles(NPs)into the overall structures of catalytic materials can not only achieve stronger metal-support interactions,but also exert their cost-effective catalysis and maximum atomic efficiency,which becomes a hot spot of researching supported noblemetal catalysts.However,the supported Au NPs with ultrafine particle size and high specific surface area often show extremely high surface activity and great thermal instability during preparation or utilization of these noble-metal materials,and thereby prone to sintering,agglomeration and deformation.Such phenomena would reduce the performance of Au nanocatalysts and shorten their service life.Additionally,these supported Au NPs are easily detached and lost from catalysts,and their recovery efficiency and utilization efficiency are also often low during utilization,which affects their practical applications.Therefore,it is of great research value and practical significance to further improve the thermal stability,utilization efficiency and catalytic performance of Au catalysts by constructing the novel structures of supported Au nanocatalysts.This thesis is based on the construction of high-efficiency catalytic systems and the improvement of thermal stability of supported Au NPs.By fully utilizing the structural advantages of yolk-shell composites,through the construction of hollow core-shell structures and the in-situ reduction of ultrafine Au NPs by means of ethylenediamine-gold precursor network immobilization method,novel supported Au yolk-shell nanocatalysts with high dispersibility and thermal stability have been prepared.Under the function of ethylenediamine ligand frameworks,the Au ions are dispersed and anchored in the yolk-shell composites with adjustable material structures and compositions.After specific reduction heat treatment,the Au NPs are in-situ loaded and encapsulated in the yolk-shell structures.Through regulating the dual support structures and partitioning cavities from the yolk-shell composites,the synergistic confinement effects of cavity structures and multi-component interactions of core/shell structures can be given full play,and the catalytic systems can be endowed with unique catalytic reaction capability.The specific research contents are summarized as follows:1.Magnetic properties in core structures are functionally constructed to endow the obtained Au catalysts with excellent magnetic separation performance.By sol-gel reactions,the Fe2O3 spindles are coated with Si O2@RF@m Si O2 composites,and RF templates are removed by calcination to obtain the yolk-shell FSVm S ellipsoids with Si O2-based double shells.By the means of DP method,Au(en)2Cl3 precursors are uniformly immobilized in FSVm S supports.By temperature-programmed hydrogen reduction heat treatment,the double-cavity magnetic yolk-shell MFSVm S-Au catalysts are obtained.Research results show that the supported Au ions are in-situ reduced into ultrafine Au NPs(3.17 nm)for encapsulation.Owing to the dual encapsulation effects of ethylenediamine ligands and Si O2 skeleton structures,these Au NPs display high dispersibility and thermal stability.The Fe2O3 spindles are simultaneously transformed into magnetic Fe particles with cavities inside the core structures,which enables the MFSVm S-Au to possess the high saturation magnetization(62.9 emu·g-1),and thereby allows their rapid separation and recycling performance.The construction of the double-cavity structures greatly strengthen the synergistic confinement of reaction processes,and promote the interaction between reaction molecules and catalytically active sites,which makes the MFSVm S-Au exhibit superior catalytic efficiency and stability than single-cavity or core-shell reference materials in the reduction of 4-NP.2.Carbon structures are adopted to promote the dispersion and solidification of Au NPs,as well as to improve their activity and thermal stability.The Si O2@RF composites are formed on the Fe2O3 spindle surfaces by the extended St?ber reaction.The yolk-shell FSVC ellipsoids with mesoporous carbon shells are obtained by carbonization-hydrothermal treatment.Through the combination of DP reaction and high-temperature hydrogen reduction method,the magnetic yolk-shell MFSAC catalysts are obtained.Research results show that,the Au(en)2Cl3 precursors anchored within the Si O2/C double-layered structures are in-situ reduced into Au NPs(2.08 nm)for encapsulation and solidification,displaying excellent dispersibility and thermal stability.The etching thickness difference of Si O2 layers during the hydrothermal process make the FSVC show two different magnetic core structures during the hydrogen reduction process,which allows the MFSAC to obtain larger effective reaction areas.The carbon structures not only produce the special ?-? interfacial effect to enhance the adsorption of the reactants,but also improve the surface electron state of the Au crystal to promote the catalysis function of Au NPs.Catalytic performance tests show that the MFSAC exhibits extremely high catalytic efficiency and excellent magnetic separation and recycling performance in the reduction of 4-NP,MB and MO molecules.3.Incorporating the metal oxides to the inner layers of core structures can improve the catalytic efficiency of the yolk-shell catalytic systems.The yolk-shell SCVm S microspheres incorporated with Ce O2 inner layers are firstly prepared.Combined with DP reaction and low-temperature hydrogen reduction method,the yolk-shell SCVm S-Au catalysts are obtained.Research results show that the Ce O2 layers are deposited on the Si O2 core surfaces to form the active metal-oxide movable carriers.The cavity structure size can be regulated by the RF layer thickness.The Au(en)2Cl3 precursors immobilized in SCVm S structures are in-situ reduced into the highly dispersed ultrafine Au NPs for encapsulation and solidification in the Ce O2/m Si O2 structures,which still maintain high dispersibility and anti-sintering properties in the hightemperature environment.Catalytic performance tests show that the hollow structures can promote the catalytic process of Au catalysts,but their reaction efficiency decreases as the cavity structure size increases.Ce O2 layers can improve the electronic structure of Au crystal,resulting in the enhanced interaction between Au and Ce O2,as well as the promotion of Au NPs' catalytic function.The construction of Ce O2-Au/m Si O2-Au double-shell nanoreactors enables the SCVm S-Au to exhibit the superior catalytic reaction efficiency than Si O2-based yolk-shell SVm S-Au and core-shell SC-Au in the reduction of 4-NP.4.Constructing the double-cavity structures can improve the catalytic performance of the yolk-shell Au catalysts incorporated with metal-oxide inner layers.RF resins are selected as core and interlayer double templates,and Ti O2 and m Si O2 layers are intercalated and coated by sol-gel reactions.After calcination treatment,Ti O2/m Si O2 yolk-shell H-TS microspheres with double-cavity structures are obtained.In conbination with DP reaction and low-temperature hydrogen reduction method,the Au NPs are in-situ prepared in the H-TS structures to obtain the yolk-shell Au catalysts.Ti O2 and m Si O2 hollow spheres are nested with each other to form the independently movable dual active composite carriers with high specific surface areas.The resulting ultrafine Au NPs are dispersed and solidified in the Ti O2/m Si O2 double-shell structures,displaying high anti-sintering properties in the harsh high-temperature environments.The formation of double-cavity structures can enhance the interaction between reaction molecules and Au catalytic sites.And under the synergistic effect of the Ti O2-Au/m Si O2-Au double-shell nanoreactors,the H-TS-Au shows the superior catalytic performance over the HT-Au and H-S-Au single-shell hollow spheres in the reduction of 4-NP.5.Incorporating the dual metal oxides as inner layers can improve the catalytic efficiency of the yolk-shell Au catalysts.By hydrothermal process,the Ni O-Ti O2 composites are modified on the surface of Si O2@Ti O2 particles to form the raspberry-like layer structures.RF@Si O2 composites are prepared on the surface,and calcined to obtain the Ni O-Ti O2 inner-layer incorporated yolk-shell SNTVS microspheres.In combination with DP reaction and lowtemperature hydrogen reduction method,Au(en)2Cl3 precursors are immobilized in the SNTVS structures to obtain the yolk-shell SNTVS-Au catalysts.During the hydrothermal process,amorphous Ti O2 is transformed into anatase crystal phase,and Ni O is doped in the Ti O2 structure to form the Ni O-Ti O2 raspberry-like composite layers on the Si O2 surface.The resulting ultrafine Au NPs(2.87 nm)are dispersed and solidified in the Ni O-Ti O2 raspberrylike layers and m Si O2 shell structures.The m Si O2 shells effectively protect the Au NPs and Ni O-Ti O2 composites.The formation of Ni O-Ti O2 heterostructures can strengthen the performance of Au catalysts.The multi-component synergistic enhancement effect of Ni OTi O2-Au/m Si O2-Au multiple active reaction interfaces from the SNTVS-Au structures,can endow the SNTVS-Au with superior catalytic performance than STVS-Au,SNVS-Au,SVSAu and SNT-Au microspheres in the reduction of 4-NP,as well as excellent recycling capability.