关键词: 催化剂, 纳米粒子, 加氢, 核壳结构, 构效关系

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