## 3 Results and Discussion
### The Characterization of the Reduced Catalysts
The peaks at 880.5, 885.3, 904.2, and 899.9 belonged to Ce\({}^{3+}\) (3d104f1 state of Ce\({}_{2}\)O\({}_{3}\)), while the other peaks  
Figure 3: X-ray diffraction patterns of the catalysts reduced at 800 \({}^{\circ}\)C. 1—Ni/CeMg-C-S-O; 2—Ni/CeMg-A-S-V; 3—Ni/CeMg-A-S-O; 4—Ni-Pd/CeMg-A-S-V; 5—Ni/CeMg-A-P-O. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{4}{c}{**600 \({}^{\circ}\)C**} & \multicolumn{4}{c}{**800 \({}^{\circ}\)C**} \\ \cline{2-9}  & **a\({}_{\text{CoO}_{2}}\)Å** & **d\({}_{\text{CoO}_{2}}\)nm** & **a\({}_{\text{NiO}}\)Å** & **d\({}_{\text{NiO}}\)nm** & **a\({}_{\text{CoO}_{2}}\)Å** & **d\({}_{\text{CoO}_{2}}\)nm** & **a\({}_{\text{NiO}}\)Å** & **d\({}_{\text{NiO}}\)nm** \\ \hline Ni/CeMg-C-S-O & 5.399 & 44 & 4.20 & 49 & - & 5.410 & 50 & 4.20 \\ Ni/CeMg-A-S-V & 5.400 & 12 & ND 1 & ND 1 & ND 1 & 5.408 & 23 & 4.20 \\ Ni/CeMg-A-S-O & 5.401 & 12 & ND 1 & ND 1 & 12 & 5.406 & 32 & 4.18 \\ Ni-Pd/CeMg-A-S-V & 5.401 & 31 & ND 1 & ND 1 & 17 & 5.404 & 36 & ND \\ Ni/CeMg-A-P-O & 5.400 & 25 & ND 1 & ND 1 & 25 & 5.404 & 34 & 4.21 \\ \hline \end{tabular}  
* Not determined due to low intensity of the peak.  
\end{table} 
Table 3: Influence of the reduction temperature on the phase composition and dispersion of catalysts. at 882.3, 888.8, 898.2, 901.0, 907.2, and 916.7 could be attributed to Ce\({}^{4+}\) (3d104f0 state of CeO\({}_{2}\)) [55]. This showed the presence of both Ce\({}^{3+}\) and Ce\({}^{4+}\). The relative concentrations of Ce\({}^{3+}\)/Ce\({}^{4+}\) are summarized in Table 4. The A catalysts had a higher Ce\({}^{3+}\) concentration compared to the C-series catalysts. In that case, each XPS peak O1s could be decomposed into three components (Figure 5) [31]. Peaks at 529.4, 531.5, and 533.1 eV corresponded to lattice oxygen, defective oxygen on the CeO\({}_{2}\) surface, and adsorbed OH or H\({}_{2}\)O particles, respectively (Table 4). The Ni-Pd/CeMg-A-S-V and Ni/CeMg-A-S-V catalysts had a higher content of defective oxygen, and more concentration of V\({}_{\rm o}\). V\({}_{\rm o}\) improves the adsorption of CO\({}_{2}\) through the formation of bicarbonates [24] and is necessary for the CO\({}_{2}\) reforming of CH\({}_{4}\)[56]. In addition, the C catalysts showed a lower concentration of defective oxygen (CDO) than the A catalysts, caused by the lower Ce\({}^{3+}\) contents. The surface molar ratio of Ni\({}^{0}\)/Ni\({}^{2+}\) increased in the series Ni-Pd/CeMg-A-S-V \(<\) Ni/CeMg-A-S-V \(<\) Ni/CeMg-A-S-O \(<\) Ni/CeMg-A-P-O. As shown in refs. [57; 58], the intensity of reoxidation increases with an increase in the dispersion and degree of MSI. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Ce\({}^{3+}\)/Ce\({}^{4+}\)1** &
\begin{tabular}{c} **Concentration** \\ **of Defective** \\ **Oxygen (\%)**2 \\ \end{tabular} & **Ni/Ce** & **Ni\({}^{0}\)/Ni\({}^{2+}\)3** \\ \hline Ni/CeMg-C-S-V & 0.19 & 17.3 & 0.06 & 0 \\ Ni/CeMg-A-S-V & 0.25 & 28.4 & 0.52 & 0.72 \\ Ni/CeMg-A-S-O & 0.23 & 26.6 & 0.32 & 0.67 \\ Ni-Pd/CeMg-A-S-V & 0.28 & 32.7 & 0.41 & 0.63 \\ Ni/CeMg-A-P-O & 0.22 & 28.1 & 1.3 & 0.77 \\ \hline \hline \end{tabular} \({}^{1}\) Calculated from XPS Ce 3d spectra. \({}^{2}\) Calculated from XPS O 1 s spectra. \({}^{3}\) Calculated from XPS Ni 2p spectra.  
\end{table} 
Table 4: XPS results of catalysts.