Preparation of yolk-shell Fe(x)O(y)/Pd@mesoporous SiO2 composites with high stability and their application in catalytic reduction of 4-nitrophenol.

Yolk-shell composites with a movable Fe(x)O(y) core and mesoporous SiO2 (mSiO2) shell, together with Pd nanoparticles uniformly anchoring on the inner surface, were prepared. The structure and composition of as-prepared catalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller measurement and Fourier-transform infrared spectroscopy, respectively. They are ideal candidates as nanoreactors for heterogeneous catalysis due to their special structure. The catalytic performance of Fe(x)O(y)/Pd@mSiO2 composites was studied by the reduction of 4-nitrophenol with NaBH4 as a reducing agent. Their reaction rate constant was calculated according to the pseudo-first-order reaction equation. The catalysts could be easily recycled by an external magnetic field due to their superparamagnetic property. Besides good catalytic property, another merit of Fe(x)O(y)/Pd@mSiO2 composites was high stability. We have compared the stability between Fe(x)O(y)/Pd@mSiO2 and Fe3O4@C/Pd composites by ultrasonic treatment and HNO3 solution etching, the stability of the former was much better than the later.