A high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image with sub-angstrom resolution further confirmed that uniform metal NPs had been formed (Figure ), and the corresponding energy-dispersive X-ray (EDX) maps showed that the Ni and O atoms were distributed homogeneously over all the NPs (Figure ). In addition, the EDX map of the recycled catalyst Ni@C-700-EtOH (recycled) (Figure ) showed no difference from the original catalyst which indicated that the reduction of acetophenone did not affect the distribution of Ni and O atoms on the NPs. The nitrogen physisorption measurements for the synthesized catalyst material in the specific surface area (Brunauer-Emmett-Teller method) were in accordance with the SEM phenomenon. Ni@C-700-EtOH has a surface area of 182 m 2 g -1 and has a pore size distribution (> 95% mesopores with a total pore volume of 0.269 cm 3 g -1 and the average pore width of 5.6 nm) (Figure ). X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) are used to study the electronic and structural properties of Ni@C-700-EtOH. XPS measurement indicated that both metallic Ni 0 and Ni 2+ species existed on the catalyst surface (Figure ). The XRD spectrum showed graphitic carbon shell C (002) between 20 and 30 which confirmed that a thin graphene shell has been formed. And it also showed that in addition to the graphite carbon shell and Ni alloy, there are also NiO phases in the samples (Figure ). This indicated that the active metal Ni species of the Ni@C catalysts prepared from the non-oxidation step were also oxidized by air after the reduction process during storage. These results indicate that the uniform nickel nano-alloy has been completely wrapped in the graphene thin shell.