Fig. 7(b) shows the characteristic peaks of metallic Ni at 2q angle
of 44.3, 51.8 and 76.4, and the peak intensity of metallic Ni
increased slightly at 2q of 44.3 with the increase in calcination
temperature. In addition, there was no obvious diffraction peaks of
CeO2 observed, indicated that the CeO2 was reduced