Hierarchical structures based on gold nanoparticles embedded into hollow ceria spheres and mesoporous silica layers with high catalytic activity and stability

Abstract

A uniform hollow CeO₂/Au@mSiO₂ core–shell catalyst with a hierarchical structure was fabricated successfully. The preparation method involves the synthesis of high surface area and porous hollow CeO₂ nanospheres, a sequential deposition of sub-10 nm Au nanoparticles to obtain CeO₂/Au, coating the particles with mesoporous SiO₂ shells through a sol–gel process and a calcination process at a desired temperature to obtain a mesoporous silica shell. The final obtained product was characterized by several techniques, including transmission electron microscopy (TEM), UV-Vis spectroscopy, X-ray diffraction (XRD) and energy dispersion X-ray spectroscopy (EDS). It is found that CeO₂/Au@mSiO₂ composite multifunctional materials have a multilayer structure and gold nanoparticles can be embedded into the hollow ceria sphere and the mesoporous silica layer. Compared with the solid CeO₂/Au@mSiO₂ catalyst, the hierarchical structures of the hollow CeO₂/Au@mSiO₂ possess open unique hierarchical pores to expose the catalytically active component, including the hollow central structure and mesopores from the CeO₂ layer and the silica shell. The results of the reduction of 4-nitrophenol (4-NP) indicate that the synthesized hollow hierarchical catalysts exhibit superior catalytic performance to the traditional core–shell structure and can be easily recycled without a decrease of the catalytic activities in the reaction.