Nano-structural changes of SnO2-supported palladium catalysts by redox treatments Original Research Article

The structural changes in Pd/SnO2 catalyst upon redox treatments were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). In the as-calcined catalyst, the fine particles of palladium species with the amorphous and the well-cyrstallized states were highly dispersed on the surface of SnO2 support due to the strong chemical interaction. The heat-treatment at 200 °C in hydrogen induced the reduction of palladium species and the particle growth, resulting in the formation of the well-crystallized Pd particles. Some peculiar structures, called the core-shell structure and the particle intrusion structure, were formed by the reduction at 400 °C. After the reoxidation treatment, the core-shell structure disappeared while the particle intrusion structure remained. Furthermore, the decrease in the mean particle diameter was confirmed in the reoxidized catalyst. The proposed formation mechanism of the unique structures from TEM observation was supported by the combination of XRD and XPS measurements.