## 3 Results
### Temperature-Programmed Reduction (TPR) and Desorption (TPD) Characterization  
The reducibility of the supports and associated Ni catalysts at increasing temperature (TPR) is shown in Figure 3A and the measured hydrogen consumption is listed in Table 3. The nC and nR carriers had two reduction regions labeled \(\beta\) and \(\gamma\), respectively. The \(\beta\) region of the nC support (Figure 3A(a)) was characterized by two overlapping peaks, with the maximum at temperatures of 495 and 538 \({}^{\circ}\)C. For the nR support (Figure 3A(c)), the reduction occurred at lower temperatures and showed a much more intense peak, with the maximum at 507 \({}^{\circ}\)C, and a weak shoulder at 400 \({}^{\circ}\)C. Besides, a slightly negative signal was highlighted at about 620 \({}^{\circ}\)C due to the concomitant reduction of carbonates that were not removed with the pretreatment. The measured hydrogen consumption was proportional to the specific surface area, i.e., nR \(>\) nC. According to the literature, these peaks are attributable to the reduction in the first layers of the ceria surface [33]. It also depends on the exposed crystallographic planes [34], which are different for cubic and nanorod morphology. In the \(\gamma\) region, reduction began with a remarkably similar trend for both supports; a single large peak with the maximum at about 900 \({}^{\circ}\)C was evident, which did not go up to the highest temperature of 1000 \({}^{\circ}\)C. This peak was due to the reduction in the bulk of ceria, which was similar for both supports, not depending on the exposed surface. The intensity was lower in the nR than in the nC, due to a more significant proportion of ceria being reduced at lower temperatures [35]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **SSA** & **Pore Volume** & **Average Pore Diameter** \\  & **(m\({}^{2}\)g\({}^{-1}\))** & **(cm\({}^{3}\)g\({}^{-1}\))** & **(nm)** \\ \hline nC & 32 & \(2.4\times 10^{-1}\) & 25 \\ Ni-nC & 33 & \(2.2\times 10^{-1}\) & 21 \\ nR & 92 & \(3.6\times 10^{-1}\) & 19 \\ Ni-nR & 62 & \(3.3\times 10^{-1}\) & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Textural properties of as-prepared samples. The TPR profiles of the Ni-catalysts depended on the morphology of the CeO\({}_{2}\) support. The reduction of Ni\({}^{2+}\) occurred in two temperature ranges, between 130-340 \({}^{\circ}\)C, called the \(\alpha\) region, and between 350-450 \({}^{\circ}\)C, i.e., superimposed on the reduction temperature of the bare CeO\({}_{2}\) surface in the \(\beta\) region. The \(\alpha\) region of the Ni-nC catalyst (Figure 3A(b)) consisted of two weak overlapping peaks at 280 \({}^{\circ}\)C, while the Ni-nR one (Figure 3A(d)) showed three more intense and overlapping peaks with a maximum at 270 \({}^{\circ}\)C. According to the literature, the \(\alpha\) peaks corresponded to the reduction of O\({}_{2}\)\({}^{2-}\)chemisorbed on the vacancies formed by some Ni\({}^{2+}\) ions in solid solution with CeO\({}_{2}\)[36]. However, a high hydrogen consumption was evident in the Ni-nR sample (0.44 mmol-g\({}^{-1}\)), which was more significant than the reduction of Ni loading itself (0.30 mmol-g\({}^{-1}\)), suggesting a remarkable reduction of the CeO\({}_{2}\) surface, as previously reported in the literature [37]. Peaks in the \(\beta\) region were assigned to the simultaneous reduction of NiO and the CeO\({}_{2}\) surface, the latter in a temperature range not different from that observed in the bare support. The hydrogen consumption of the Ni-nC sample (0.44 mmol-g\({}^{-1}\)) in the \(\alpha\) and \(\beta\) regions was very similar to what would be expected from the reduction of NiO and the CeO\({}_{2}\) surface of the bare support, indicating a lower interaction of NiO, with CeO\({}_{2}\) having a nanocube morphology.