In order to confirm the crystal structures of these two catalysts, typical X-ray diffraction (XRD) patterns were carried out using Cu Kα radiation (Figure ). The intense and sharp XRD peaks (Figure above) indicate that all diffraction peaks of the CoNiCuFe-PBA coincide well with the standard card (JCPDS: 51-1897), corresponding to the (111), (200), (220), (400), (420), (422), (440), (600) planes, respectively. Besides, it is evident that the CoNiCuFe-PBA exhibited a single-phase, the Fm-3m face-centered cubic (FCC) structure, and a superior crystallinity than the CoNiCuFe-Oxide (Figure below). The CoNiCuFe-Oxide is mainly composed of Ni0.1Co0.5Cu0.4Fe2O4 (JCPDS: 52-1798) with much poorer crystallinity. The corresponding standard XRD patterns below of the CoNiCuFe-Oxide can be assigned to a face-centered cubic structure with an Fd-3m space group. More specifically, the crystallinity of CoNiCuFe-PBA and CoNiCuFe-Oxide calculated by XRD patterns were 99.1%, 66.7%, respectively. Therefore, the well-crystallized CoNiCuFe-PBA and amorphized CoNiCuFe-Oxide catalysts were successfully prepared. The morphologies of the two catalysts were characterized and compared through transmission electron microscopy (TEM) images. The CoNiCuFe-PBA exhibited a regular cubic shape (Figure ), and the surface of cubic PBA structures has no obvious amorphous layers. The selected area electron diffraction (SAED) pattern (Figure ) showed clear diffraction spots corresponding to the crystal planes of ( ), (400), ( ) and (800), indicative of a good crystalline structure of CoNiCuFe-PBA. Distinctively, the CoNiCuFe-Oxide retained the original cubic morphology but became the hollow architectures due to the annealing at 500 °C (Figure ). Also, the SAED pattern of CoNiCuFe-Oxide showed possession of more amorphous structures. Meanwhile, the energy dispersive spectroscopy (EDS) elemental mapping images in Figure show that the Co, Ni, Cu, and Fe elements are homogeneously distributed for CoNiCuFe-PBA. The compositions of CoNiCuFe-PBA and CoNiCuFe-Oxide catalysts were determined through EDS analysis (Table ), which is in line with the stoichiometry during the preparation.