In continuation of our previous work (J. Phys. Chem. Lett. 2010, 1(20), 3141 and J. Phys. Chem. C 2010, 114 (45), 19194), Fe3O4@Au core-shell types of nanoparticles were prepared by coating superparamagnetic iron oxide nanoparticles (SPIONS; similar to 4.9 nm) with a thin layer of gold (similar to 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 degrees C in either (a) a reducing atmosphere with H-2/Ar or (b) an oxidizing atmosphere with O-2/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/TiO2 was 5.96 +/- 0.71 nm. Fresh and pretreated programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. To test the activity of Fe3O4@Au/TiO2 catalysts, CO oxidation was performed over catalysts from 30 to 500 degrees C. Results showed that the catalyst treated with H-2/Ar at 500 degrees C had a lower light-off temperature and the highest CO conversion (similar to 68%) at 300 degrees 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 H-2 at 500 degrees C can be attributed to the copresence of Fe-0 and Au-0 in the catalyst, the complete removal of organic ligands from the catalyst surface, and possibly the synergistic interaction between Au and Fe.
2012. Vol. 116, no 42, 22319-22326 p.