| Abstrakt: |
In continuation of our previous work (J. Phys. Chem. Lett.2010, 1(20), 3141 and J. Phys. Chem. C2010, 114(45), 19194), Fe3O4@Au core–shell types of nanoparticles were prepared by coating superparamagnetic iron oxide nanoparticles (SPIONS; ∼4.9 nm) with a thin layer of gold (∼0.5 nm) and supported on microporous TiO2. To remove the ligands attached to nanoparticles, the catalyst was treated at 200, 300, 400, and 500 °C in either (a) a reducing atmosphere with H2/Ar or (b) an oxidizing atmosphere with O2/He. The synthesized nanoparticles and freshly prepared catalysts were characterized by HRTEM, which revealed that the size of the Fe3O4@Au nanoparticles was 5.34 ± 0.71 nm and that of Fe3O4@Au/TiO2was 5.96 ± 0.71 nm. Fresh and pretreated catalysts were further characterized by temperature programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. To test the activity of Fe3O4@Au/TiO2catalysts, CO oxidation was performed over catalysts from 30 to 500 °C. Results showed that the catalyst treated with H2/Ar at 500 °C had a lower light-off temperature and the highest CO conversion (∼68%) at 300 °C; however, such a treatment also resulted in catalyst sintering, leading to a net increase in particle size to 7.87 ± 1.59 nm. The higher catalytic activity of the catalyst treated with H2at 500 °C can be attributed to the copresence of Fe0and Au0in the catalyst, the complete removal of organic ligands from the catalyst surface, and possibly the synergistic interaction between Au and Fe. |
