Abstract:

Two novel magnetic mesoporous core-shell nanocomposites Ni@mSiO₂ and Ni-N₂H₄@mSiO₂ were prepared by a surfactant-templating method. Nickel nanoparticles were first obtained from nickel nitrate or nickel chloride by thermodecomposition and hydrazine hydrate reduction, then covered by a mesoporous shell, and finally by sinteration and hydrogen reduction. As a comparison, Ni/mSiO₂ carrier supporting catalyst was prepared by the traditional coprecipitation method. The core-shell nanocomposite of nickel nanoparticle core and mesoporous silica shell was characterized by transmission electron microscopy, X-ray diffraction and nitrogen adsorption-desorption. Temperature programmed H₂ reduction indicated that NiO in these catalysts were mainly present in bulk phase and some small NiO particles in Ni-N₂H₄@mSiO₂ were easily reduced. H₂-chemsorption results demonstrated that Ni/mSiO₂ had more active sites but lower TOF value compared to core-shell Ni@mSiO₂ and Ni-N₂H₄@mSiO₂ catalysts. Both Ni@mSiO₂ and Ni-N₂H₄@mSiO₂ showed higher activity and better selectivity than Ni/mSiO₂ in selective hydrogenation of cinnamyl aldehyde to hydrocinnamaldehyde, with over 90% yield of hydrocinnamaldehyde. Due to high magnetic saturation value of Ni-N₂H₄@mSiO₂, it can be easily recycled for reuse by an external magnetic field. Notably, Ni-N₂H₄@mSiO₂ showed better stability in hydrogenation.

Key words: catalyst, nano particle, hydrogenation, core-shell structure, structure-function relationship

摘要：

分别以硝酸镍和氯化镍为镍源，利用热分解法和水合肼还原法制得镍纳米粒子，再经模板剂造孔法在镍核外部包裹一层介孔壳，通过焙烧和氢气还原制备了核壳结构催化剂Ni@mSiO₂和Ni-N₂H₄@mSiO₂，并以肉桂醛加氢为探针反应考察了核壳结构镍基催化剂与负载型镍基催化剂的加氢性能。结果表明，核壳结构镍基催化剂在肉桂醛加氢反应中比共沉淀法制备的负载型镍基催化剂具有更高的活性，氢化肉桂醛的收率可达90%以上。同时，Ni-N₂H₄@mSiO₂催化剂具有较高的磁饱和度，可实现该催化剂在反应后高效回收并循环套用。采用X射线衍射、比表面及孔分析、透射电子显微镜、H₂-程序升温还原和H₂-化学吸附等表征手段，研究了所制催化剂的结构特征，初步探讨了催化剂结构与性能的构效关系。

关键词: 催化剂, 纳米粒子, 加氢, 核壳结构, 构效关系