## 3 Results  
### Structural and Morphological Characterization  
The XRD patterns of the nR and nC supports and the Ni-nR and Ni-nC catalysts are shown in Figure 1A, and the corresponding Williamson-Hall (W-H) plots are given in Figure 1B. The main structural features are listed in Table 1. After calcination at 550 \({}^{\circ}\)C, the nR and nC supports showed the peaks corresponding to the diffraction planes (111), (200), (220), (311), (400), and (331) of the cubic structure with Fm3-3m space group (JCPDS 34-0394). The diffraction angle of these peaks was similar for both samples. However, the FWHM was much larger in the nR support, indicating a smaller crystallites size. In fact, from the intercept with the y-axis of the W-H plot, a crystallite size of 10 nm was calculated for the nR, compared to a much larger size, of 40 nm, obtained for the nC. The \(\varepsilon\) strain, resulting from the slope of the line, was also slightly different, being 1.7 \(\times\) 10\({}^{-3}\) and 1.4 \(\times\) 10\({}^{-3}\) for the nR and nC supports, respectively. Confirming a larger crystalline imperfection for the nanorod morphology, even if these defects did not change the lattice parameter, which was equal to 5.41 A in both supports. Introducing Ni during the synthesis significantly changed the crystallographic patterns of the catalysts calcined at 550 \({}^{\circ}\)C. Peaks at 20 angles 37.3\({}^{\circ}\), 43.3\({}^{\circ}\), and 62.9\({}^{\circ}\) corresponding to diffraction planes (111), (200), and (220) of the cubic NiO phase with space group Fm3-3m (JCPDS 47-1049) were clearly visible, albeit with very low intensity due to the small amount of Ni in the catalysts (1.75 wt%). The width of these peaks was much larger in Ni-nR than in Ni-nC, and the crystallite sizes, estimated by the Scherrer equation, were 20 and 71 nm, respectively. From W-H diagrams of CeO\({}_{2}\) phase, crystallites of 18 nm and 32 nm with the strain of 1.4 \(\times 10^{-3}\) and 1.5 \(\times 10^{-3}\) were obtained for the Ni-nR and Ni-nC catalysts, respectively. The Ni-nR lattice parameter of 5.40 A was slightly lower than that of Ni-nC, which was 5.41 A. Thus, the introduction of Ni seems to reduce the crystallographic differences between the two morphologies. However, as reported by several authors [30; 31], it cannot be ruled out that some of the Ni has been incorporated into the CeO\({}_{2}\) lattice to form a solid Ce-O-Ni solution. The N\({}_{2}\) adsorption/desorption isotherms and the corresponding pore size distributions of the materials are shown in Figure 2, and the main textural properties are summarized in Table 2. All samples showed II-type adsorption-desorption curves, with H2-type hysteresis loop (IUPAC classification [32]), characteristic of macroporous materials. The specific surface area (SSA) of pure cera was 32 m\({}^{2}\)g\({}^{-1}\) for nC morphology, and 92 m\({}^{2}\)g\({}^{-1}\) for nR morphology, agreeing with the different crystallite dimensions measured by XRD analysis. The addition of nickel led to a decrease in SSA of about 30% (62 m\({}^{2}\)g\({}^{-1}\)) only for the nR morphology, whereas it did not affect the surface area for the nanocube morphology. Bare nC and nR supports showed a Barrett-Joyner-Halenda (BJH) total pore volume equal to 0.24 and 0.36 cm\({}^{3}\) g\({}^{-1}\), respectively. The addition of nickel caused an identical slight pore volume decrease of 8.3% in both samples (Table 2). The pore size distributions (PSD) for both structures showed a bimodal distribution with two maxima; one in the mesopores region (<10 nm), and another in the meso-macroopres region (>50 nm). For the nC morphology, the maximum of the mesopores was centered at 2.5 nm, and that of the meso-macroopres maximum at around 40 nm. The addition of nickel did not affect the overall distribution, probably due to a lower interaction between the metal and the