Gold nanoparticles: effect of treatment on structure and catalytic activity of Au/Fe2O3 catalyst prepared by co-precipitation

1 wt% Au/Fe2O3 catalyst was prepared by a co-precipitation method. The structure of the sample in the as prepared, oxidized and reduced states was investigated by means of X-ray photoelectron spectroscopy (XPS), transition electron microscopy (TEM), electron diffraction (ED) and X-ray diffraction (XRD). The structure of the samples after various treatments and their activity in the CO oxidation were compared. The results show the stability of the gold particle size during the treatments. However, after oxidation, a slight shift in the Au 4f binding energy towards lower values points to the formation of an electron-rich state of the metallic gold particles compared to that revealed in the as prepared sample. Simultaneously, a goethite phase in the Fe2O3 support is present, which is not observed in the as prepared and reduced samples. In the reduced sample the presence of a crystalline maghemite-c phase indicates a change in the support morphology. In the CO oxidation the oxidized sample shows the highest activity and it might be the result of the cooperative effect of goethite, FeO and the electron-rich metallic gold nanoparticles. We suggest that a structural transformation occurs along the gold/support perimeter during the treatments and we propose a possible mechanism for the effect of the oxidation treatment.