*2.6. Crystallite Structure of Ni-xSi/ZrO2 Catalysts*

The XRD patterns of catalysts could be seen in Figure 7. Before reduction, the diffraction peaks at 37.2, 43.3, and 62.9◦ were attributed to NiO (PDF no. 47-1049), as shown in Figure 7a [1,26]. The diffraction peaks at 44.5, 51.8, and 76.4◦ corresponded to the Ni metal (PDF no. 04-0850) over reduced catalysts, as shown in Figure 7b, and there was no diffraction peak of NiO [57]. In addition, no obvious diffraction peak of Si species was detected on Ni-xSi/ZrO2 catalysts, suggesting that Si was in a high dispersion or amorphous state [51]. The crystallite sizes of NiO and Ni metal were calculated by the Scherrer equation at 2 θ = 43.3◦ and 2 θ = 44.5◦, respectively, and the results were listed in Table 5. It could be seen that the particle sizes of NiO had no significant changes and the crystallite sizes of NiO were all around 25 nm on Ni-xSi/ZrO2 catalysts before reduction. The grain sizes of the Ni metal were around 22 nm on reduced Ni-xSi/ZrO2 catalysts, which also showed no obvious variation.

**Figure 7.** XRD patterns of Ni-xSi/ZrO2 catalysts (**a**) before reduction, (**b**) after reduction.

**Table 5.** The crystallite sizes of NiO and Ni metal on Ni-xSi/ZrO2 catalysts.

