*2.4. The H2-TPD and H2-Chemisorption of Ni-xSi/ZrO2 Catalysts*

The amounts of active sites of reduced Ni-xSi/ZrO2 catalysts were measured by H2- TPD and H2-chemisorption. Two peaks could be clearly observed in the patterns of reduced catalysts depicted in Figure 5. The first peak appeared at around 92–111 ◦C, which was assigned to the weak active site, and a broad peak around at 500 ◦C could be found over the catalysts, corresponding to the strong active site with the strong H2 adsorption [51,52]. The temperature of two H2 desorption peaks was different with different contents of Si. The highest temperature with 111 and 517 ◦C of H2 desorption peaks on the Ni-0.1Si/ZrO2 catalyst suggested the strong H2 adsorption to the active sites, which could be assigned to the high dispersion of Ni and the increasing number of active sites [51–53]. Considering the possible spill over in TPD over the catalysts, the pulse chemisorption of H2 was also carried out. The dispersion of Ni obtained by H2-chemisorption was shown in Table 3. The Ni dispersion of Ni/ZrO2, Ni-0.1Si/ZrO2, Ni-0.5Si/ZrO2, and Ni-1Si/ZrO2 were 0.65%, 0.67%, 0.34%, and 0.28%, respectively. The Ni-0.1Si/ZrO2 catalyst showed the highest dispersion of Ni, which was slightly higher than the Ni/ZrO2 catalyst. The amounts of adsorbed H2 decreased significantly on Ni-0.5Si/ZrO2 and Ni-1Si/ZrO2 catalysts, suggesting that the amounts of Ni decreased, which corresponded to their lower catalytic activity.

**Figure 5.** H2-TPD patterns of Ni-xSi/ZrO2 catalysts.


**Table 3.** The H2 uptake and Ni dispersion of Ni-xSi/ZrO2 catalysts.

a: Obtained by H2-TPD; b: Obtained by H2 chemisorption.
