Preparation And Properties Of Nano-pt-based Catalysts Encapsulated By Metal Oxide

The supported Pt nanocatalysts have been widely used in many fields such as chemical engineering,energy,medicine etc,because of its unique catalytic activity and high selectivity.The catalytic performance of the supported Pt nanocatalysts is mainly effected by the active component and carrier.On the one hand,the support with mesoporous morphology can disperse the loaded Pt nanoparticles more evenly.On the other hand,these metal oxides can make the catalysis more efficient by the synergism with the active sites.In this paper,in order to improve the stability and catalytic performance of Pt nanocatalysts,template method is used to prepare mesoporous metal oxides and metal oxides shell with different morphology.Afterwards,the prepared metal oxide was used as a carrier to encapsulate Pt nanoparticles.The effects of composite metal oxide support on the catalytic performance of Pt nanometallic catalysts were investigated.Finally,the reduction of nitrophenol was chosen to evaluate the performance of the catalyst.Combining all the characterization and analysis data,the main results are as follows:1.Mesoporous ZrO₂ and La₂O₃-ZrO₂ composites were prepared by hard template method using mesoporous silica as the sacrificial template agent.Subsequently,PtDENs/ZrO₂ and PtDENs/La₂O₃-ZrO₂ were obtained by loaded Pt NPs encapsulated by 4-hydroxyl-terminated poly（amidoamine）（G4-OH PAMAM）dendrimers.The morphologies and structures of the catalysts were characterized by TEM,BET,EDX,XRD and XPS.The results showed that Pt nanoparticles retained smaller size.Furthermore,the reduction of p-nitrophenol was utilized to evaluate the catalytic performances of catalysts.In catalytic performance tests,Pt/La₂O₃-ZrO₂ catalyst calcined in nitrogen at 550°C exhibited higher catalytic activity and cycle performance.It is further demonstrated that the introduction of La can improve the structure of the carrier and the catalytic efficiency of the Pt supported nanocatalysts.2.A novel strategy has been developed to synthesize metal oxide（e.g,La₂O₃,CeO₂ and La₂O₃-CeO₂）double-shelled hollow nanospheres（MDSHs）.This method involves the formation of mesoporous hollow SiO₂,dipping,calcination and etching,which avoids tedious procedures compared with traditional synthetic strategy.After that,the Pt NPs are loaded into the MDSHs.The every step in this project was characterized by TEM,SEM and XRD.Results indicate that all of MDSHs possess double-shelled structures with both the inner and outer shells composing of metal oxide units.The metal oxide of the DHSs can offer abundant active points for Pt NPs and the void between the double shells also could be filled with Pt NPs.In the reduction of p-nitrophenol,the Pt-embedded La₂O₃-CeO₂-DSHs exhibited significantly enhanced catalytic performance compared with the pure Pt-based-La₂O₃-DSHs and Pt-based-CeO₂-DSHs.3.Pt nanoparticles are deposited on the ellipsoids Fe₂O₃,which is prepared by the hydrothermal method.Then the Fe₂O₃-Pt@HMS was synthesized through the etching and redepositing of silica layer.Pt-loaded yolk-shell nanocomposites ellipsoids（Fe₂O₃-Pt@DSL）was fabricated using Fe₂O₃-Pt@mSiO₂ as template sacrificial agent,digging and etching.After characterization of the samples,results indicated that the Fe₂O₃-Pt@DSL nanocomposites possessed mesoporous structure and tunable shell thickness.Moreover,in the reduction of p-nitrophenol,the Fe₂O₃-Pt@DSL catalyst showed the superior catalytic activity and reusability due to the structural superiority and enhanced composite synergy.