Controlled Synthesis And Catalytic Properties Of Iron Cobalt Silicate With Mesoporous Structure

Nanocomposite materials with core-shell structure have potential application value in catalysis,packing,drug carrier,biological medicine and multifunctional coating material,which have better properties than single component materials.Transition metal catalysts with high thermal stability,easy and cheap raw materials,are widely used in the nitrobenzene liquid hydrogenation reaction.The study and results of this dissertation can be summarized as follows:1.Hydrothermal preparation and characterization of iron silicate with mesoporous structure.Mesoporous iron silicate hollow microspheres were synthesized via hydrothermal method using SiO₂ microspheres as templates.The synthetic mechanism has carried on the preliminary discussion.Study found that the morphology and phase composition are influenced by different alkaline environment.Iron oxide was abtained in the non-alkaline environment.Uniform remella microspheres were synthesized with Si/Fe ratio of 1:2.With the extension of reaction time,the structure of hydrothermal products by core-shell structure changes into hollow structure.Nanocomposite materials with core-shell structure or hollow structure can be synthesized by adjusting the reaction time.The specific surface area of iron silicate with mesoporous structure was 142.2 m2/g.2.Study on the synthesis and catalytic properties of Fe/SiO₂ with mesoporous structure.Iron silicate hollow microspheres with mesoporous structure were reduced in hydrogen atmosphere for 3 h at 600 °C,and then Fe/SiO₂ composite microspheres catalyst were obtained.The size and morphology of the microspheres still keep the hollow structure before and after reduction.The catalytic activity of Fe/SiO₂ was evaluated by the nitrobenzene hydrogenation reaction.The results show that the rate of catalytic reaction is accelerated by increasing reaction temperature.The conversion rate of the nitrobenzene reached 75% and the selectivity rate of the aniline attained 83% at catalyst temperature of 100 °C for 5 h.Catalytic activities of Fe/SiO₂ catalysts were increased with the extension of hydrothermal time.Compared with other temperatures,the products of 24 h have larger surface area and better catalytic effect than others.3.Hydrothermal-reduction synthesis and catalytic property of Fe/SiO₂.Cobalt silicate hollow microspheres with mesoporous structure were obtained at 180 °C for 12 h,and were reduced to mesoporous Co/SiO₂ hollow microspheres in hydrogen atmosphere.The specific surface areas of the samples before and after reduction were 382.78 m2/g,158.25 m2/g,respectively,but the same morphology.The catalytic activity of Co/SiO₂ for the catalytic hydrogenation of nitrobenzene to produce aniline was studied.Under the alkaline hydrothermal environment,iron-cobalt silicate composite microspheres with uniform size and stable morphology were obtained with Fe/Co ratio of 1:2.The results show that the reaction rate can be speed up by increasing the temperature,but the high temperature may lead to hollow structure instability and collapse.Iron-cobalt silicate microspheres with mesoporous structure were reduced to mesoporous Fe-Co/SiO₂ hollow microspheres with big specific surface area in hydrogen atmosphere.The structure of Fe-Co/SiO₂ is conducive to the transmission of material and improves the catalytic performance.Results showed that the catalytic activity of bimetallic catalysts was higher than that of single metal catalysts owing to the synergistic effect between two metals.