Preparation And Properties Of Mixed-oxide-coated Au Nanocatalyst

Due to their high catalytic activity,gold nanoparticles have attracted the attention of researchers in recent years.In particular,supported gold catalysts have been found to catalyze many types of chemical reactions such as hydrocarbon oxidation,methanol production,water vapor shift reactions and the like.Among the many supported nano gold catalyst carriers,some oxides,such as TiO₂,CeO₂,ZrO₂ and the like,have good redox properties and strong oxygen storage oxygen releasing ability or excellent anti-roasting property and are considered to be excellent in gold Vector.In addition,the morphologies of different catalysts,the specific surface area and pore structure vary greatly,will directly affect the catalytic activity of the gold catalyst.In this paper,a series of gold nanocatalysts with hollow structure were prepared by encapsulating gold nanoparticles with composite oxides,combining the advantages of different metal oxides and the synergistic effect between metal oxides and gold nanoparticles.The details are as follows:1.A novelbinary-metal-oxide-coated hollow microspheres-titanium dioxide-zirconium dioxide-coated Au nanocatalyst was prepared via a facile hydrothermal synthesis method.SEM,TEM,EDX,FT-IR,XRD,UV–vis and XPS were employed to characterize the composition,structure,and morphology of ZrO₂-TiO₂ hollow spheres.The size of Au NPs was found to be 3-5 nm in diameter before being immobilized on the aforementioned mesoporous TiO₂-ZrO₂ layer and used as catalysts in the reduction of 4-nitrophenol to 4-aminophenol by NaBH₄.Compared with TiO₂/Au and ZrO₂/Au,TiO₂-ZrO₂/Au NPs shows a higher catalytic activity for mixed oxide synergistic reaction.Besides,the hollow TiO₂-ZrO₂/Au nanospheres were calcined at 700,550 and 300°C,respectively,the sample calcined at 550°C showed the highest thermal stability and reactivity.Finally,to explain the reduction of 4-nitrophenol to 4-aminophenol,a possible reaction mechanism was also proposed.2.This work reports a novel type of sandwich-like hollow Au-based nanocatalyst,including a TiO₂-ZrO₂ shell,a hollow CeO₂ core and Au nanoparticles of 2-5 nm.Uniform crystal ceria hollow nanostructure were synthesized by a simple one-step hydrothermal method without template.Then the binary TiO₂-ZrO₂ coated Au nanocatalyst was prepared via a facile bottom-up synthesis method.The structural features of catalysts were characterized by several techniques,including SEM,TEM,EDX,FT-IR,BET,XRD,UV-vis and XPS analyses.Using the reduction of4-nitrophenol by NaBH₄ as a model reaction,TiO₂-ZrO₂/Au/CeO₂ microspheres showed a superior catalytic activity and thermal stability compared with a pure TiO₂or ZrO₂ layer.Besides,the calcined TiO₂-ZrO₂/Au/CeO₂ microspheres at 700°C presented the highest thermal stability and reactivity.This comparative results were mainly attributed to the synergistic effect among mixed oxide,hollow CeO₂ core and Au NPs and the sandwich-like structure.As a consequence,the unique nanocatalyst will open a promising way in the fabrication of the hollow binary-metal-oxide materials for future research and has great potential in other applications.3.A novel magnetic binary-metal-oxide-coated nanocataly composing of a hollow Fe₃O₄ core and CeO₂-La₂O₃ shells with Au nanoparticles encapsulated has been created in this work.The structural features of catalysts were characterized by several techniques,including SEM,TEM,UV-vis,FT-IR,XRD,XPS and TGA analyses.After the coating of CeO₂-La₂O₃ layer,CeO₂-La₂O₃/Au/C/Fe₃O₄microspheres showed a superior thermal stability and catalytic reactivity compared with a pure CeO₂ or La₂O₃ layer.Accompanied by the burning of carbon layer,the specific surface could be increased by the formation of double-shelled structure.Besides,the desired samples could be separated by magnet,implying the superior recycle performance.Using the reduction of 4-nitrophenol by NaBH₄ as a model reaction,the microspheres exhibited highly reusability,superior catalytic activity,thermal stability,which are attributed to the unique double-shelled structure of the support,uniform distribution of Au nanoparticles,the highly thermal stability of CeO₂-La₂O₃ layer and mixed oxide synergistic effect.As a consequence,the unique nanocatalyst will open a promising way in the fabrication of the double-shelled hollow binary-metal-oxide materials for future research and has great potential in other applications.