Preparation of yolk-shell Fe_xO_y/Pd@mesoporous SiO₂ composites with high stability and their application in catalytic reduction of 4-nitrophenol

Yolk-shell composites with a movable Fe_xO_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_xO _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_xO_y/Pd@mSiO₂ composites was high stability. We have compared the stability between Fe_xO _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.