*2.1. XRD Analysis*

Figure 1a shows the XRD patterns of the Ni-Mo sulfide/Al2O3 catalysts with different Ni/Mo molar ratios. The characteristic diffraction peaks of each catalyst observed at 2θ about 14.4◦, 32.7◦, and 58.4◦ were attributed to the (0 0 2), (1 0 0), and (1 1 0) planes of MoS2 (JCPDS#65-1951), respectively. Similarly, the peaks located at 2θ of 27.2◦, 31.5◦, 35.3◦, 38.8◦, 45.1◦, 53.5◦, 56.1◦, 58.6◦, and 61.0◦ were assigned to the (1 1 1), (2 0 0), (2 1 0), (2 1 1), (2 2 0), (3 1 1), (2 2 2), (0 2 3), and (3 2 1) crystal surfaces of the NiS2 phase (JCPDS#65-3325), respectively. Meanwhile, the diffraction peaks of Al2O3 were also detectable. Especially, the XRD patterns also exhibited a variation trend correlated to the chemical compositions. With an increase in the Ni/Mo molar ratio, the diffraction peaks shifted to slightly higher 2θ values, as seen in Figure 1b. The Ni2<sup>+</sup> ions replaced the position of Mo ions or entered the gap position of MoS2 to form the Ni-Mo-Sx phase [15]. Since the radius of Ni2<sup>+</sup> ion is bigger than the radius of Mo4<sup>+</sup> ion, the lattice parameters of Ni-Mo sulfides increased with increasing Ni content. Therefore, it can be deduced that the weak diffraction peaks of MoS2 with an increase in the content of Ni may be related to the formation of the Ni-Mo-Sx phase. In addition, the other Ni and Mo species were in the states of NiS2 and MoS2, respectively. These sulfides were uniformly mixed, owing to the metal ions being uniformly dispersed on the support. In other words, Ni-Mo-Sx, NiS2, and MoS2 were well mixed and highly dispersed on the support.

In addition, the weak and broad peaks illustrate that the sulfide particles were highly dispersed with particles in small nanoscale size. Based on the Scherrer equation, the average particle sizes of the Ni-Mo sulfide/Al2O3 catalysts were calculated. As shown in Table 1, the average particle sizes were estimated to be 7.8, 9.1, 10.2, 11.5, and 13.9 nm for the Ni-Mo sulfide/Al2O3 catalysts of which Ni/Mo molar ratios were 2/6, 3/5, 4/4, 5/3, and 6/2, respectively, which is agreemen<sup>t</sup> with the sizes of the nanoparticles in the TEM analysis. Moreover, as the Ni/Mo molar ratio increased, the average particle sizes gradually increased. The change in the average particle size can be explained by an increase in the Ni content. In addition, the surface areas of the various Ni-Mo sulfide/Al2O3 catalysts are compared in Table 1. It seems that the Ni/Mo molar ratio did not significantly affect the surface areas.

**Figure 1.** The XRD patterns of the Ni-Mo sulfide/Al2O3 catalysts with different Ni/Mo molar ratios (**a**) scanning angle of 10–90◦; (**b**) scanning angle of 30–32.8◦.

**Table 1.** BET surface areas, particle sizes, and band gaps of the various Ni-Mo sulfide/Al2O3 catalysts.

