Synthesis And Catalytic Performance Of Noble Metal-Oxide Core-shell/Rattle Nanocatalysts

This thesis aims to control the synthesis of noble metal core-shell nanostructures,and to use the interaction between noble metal-metal oxides and the protection of shells to prepare novel nanocatalysts with hight performance than single-metal nanomaterials.Compared with the single metal catalyst synthesized under the same conditions,the synthesized noble metal-oxide core-shell/rattle nanocatalysts exhibits excellent catalytic performance in the oxidation reaction of carbon monoxide.The experimental data show that the synergistic interaction between noble metal and metal oxide can control the electronic structure of the catalytic active center and improve the catalytic performance.The confinement effect of the thermally stable shell prevents the agglomeration of the nanoparticles and improves the anti-sintering performance.The specific research contents are as follows:?1?The Au-FeO_x@SiO₂ core-shell catalyst was synthesized by the method of co-precipitation combined with water-in-oil?W/O?reverse microemulsion.The effects of different synthesis conditions on the morphology of Au-FeO_x@SiO₂ core-shell catalysts were investigated in detail by TEM images.A series of Au-FeO_x@SiO₂ core-shell nanocatalysts with Au/Fe ratios of 3:0,3:1,3:3,3:6,and 3:9 were prepared.The samples were characterized by XRD,UV-Vis,H₂-TPR and other techniques.The characterization results show that there is a strong interaction between Au and FeO_x in the Au-FeO_x@SiO₂core-shell catalyst.The BET specific surface area and pore volume were calculated from the N₂ gas adsorption desorption isotherm of the sample.It is shown that the BET specific surface area and pore volume of the Au-FeO_x@SiO₂ core-shell catalyst increase with the increase of Fe content.The catalytic activity of Au-FeO_x@SiO₂ core-shell catalyst for CO oxidation showed that the FeO_x produced has close contact with Au clusters,and improved the porosity of SiO₂ shell by affecting the TEOS condensation.Both of these effects are contribute to the high CO oxidation activity.The combination of the active Au-FeO_x phase and the core-shell structure achieves high activity and good thermal stability with the same catalyst.?2?The Au-FeO_x@ZrO₂ rattle core-shell catalyst was synthesized by using the synthesized silica nanoparticles as a hard template.The synthesis conditions of Au-FeO_x@ZrO₂ rattle core-shell catalysts were characterized.The effects of different conditions parameters on the morphology of the catalysts were discussed.The catalytic oxidation of CO showed that the catalytic activity increased with the increase of Au loading,and the introduction of amorphous FeO_x could significantly promote the activity of the catalyst in the case of low Au content.However,this promotion decreases with the increase in the loading of Au and is even detrimental to the activity of the catalyst.This may be due to the strong interaction between amorphous FeO_x and Au NPs and ZrO₂ at low Au content,which promotes its activity.When the Au content increases,ZrO₂ remains unchanged.Part of the Au-FeO_x is detached or even completely destroyed by the cavity ZrO₂ structure,resulting in a decrease in catalytic activity.The activity of the Au-FeO_x@ZrO₂ core-shell catalyst is mainly caused by the interaction of between three substances,Au-FeO_x-ZrO₂.?3?Considering the difference of standard reduction potential of Fe³⁺/Fe²⁺?0.77 V?and Mn₃O₄/Mn²⁺?1.82 V?,the Fe²⁺ion was used to reduce Mn³⁺ions in Mn₃O₄ nanoparticles to prepare Hollow-Mn_3-xFe_xO₄ nanoparticles.Then,the reduction potential of PtCl₄^2-/Pt pair increase under high temperature conditions,and the reduction potential of Mn₂O₃/Mn₃O₄pair decreases with increasing temperature to facilitate the electrochemical displacement deposition of Pt.The displacement process of the two-step Galvanic Replacement?GR?reaction was confirmed by XRD and TEM characterization.A simple activity test was carried out on the synthesis of Pt/Hollow-Mn_3-xFe_x O₄ hollow core-shell catalyst,indicating that its catalytic activity is temperature-sensitive.