## 3 Results and Discussion
### Catalytic Performance
The XRD pattern of the spent catalysts is displayed in Figure 8. In Ni-Pd/CeMg-A-S-V, a small amount of the Ni\({}^{0}\) phase was detected by XRD, probably due to the reoxidation of fine particles of metallic nickel upon contact with air, which is consistent with the XPS data. Peaks related to deposited carbon (ICSD 53781) were observed in particular in the Ni-Pd/CeMg-A-S-V and Ni/CeMg-A-S-V catalysts, in agreement with the TGA results. No NaCl phase was observed in spent catalysts, which confirmed the removal of salt during the reaction. The intensity of the Ni\({}^{0}\) diffraction peak increased compared to reduced catalysts that could result from an increase in the quantity of the metallic Ni and the coarsening of crystallites due to sintering. It is noted that, in contrast to the spent catalysts of the A series, in the spent C catalyst, there was no Ni\({}^{0}\) phase, which explained its low activity (Figure 5). The Ni crystallite size in the spent A catalysts increased in the next sequence: Ni-Pd/CeMg-A-S-V (16 nm) \(<\) Ni/CeMg-A-S-V (31 nm) \(<\) Ni/CeMg-A-S-O (46 nm) \(<\) Ni/CeMg-A-P-O (83 nm). The Ni-Pd/CeMg-A-S-V and Ni/CeMg-A-S-V samples with a lower rate of deactivation had a higher quantity of carbon deposits. This meant that these differences in the stability of the samples were caused by the differences in their agglomeration properties not in their coking resistance. The weak interaction of Ni with the support and the low thermal stability of the support in the A-S-O catalyst caused a Ni agglomeration upon thermal treatment (Table 3), which also led to its deactivation during the reaction. As a result, at the earlier stage of the reaction, the A-S-O catalyst displayed a high activity, while the A-S-O catalyst was deactivated faster with time on stream than the A-S-V catalysts. It was shown in [65] that the oxygen storage capacity was a secondary  
Figure 7: TGA profiles for the catalysts after the CSMR reaction at 750 \({}^{\circ}\)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. factor influencing the catalytic efficiency. It was established that mobile oxygen inhibited carbon formation by reacting with carbon and improved catalytic performance [23; 25; 66]. The effectiveness of the carbon removal mechanism depends on CDO and the metal particle size [67]. The CDO effect is strengthened by heavily dispersed metallic particles deposited on reducible oxides and having a higher metal-support interface. In comparison to the Ni/CeMg-A-S-V sample, Ni-Pd/CeMg-A-S-V was characterized by a higher dispersion, CDO, and a lower amount of deposited carbon. The Ni/CeMg-A-P-O (P-series) exhibited the lowest amount of deposited carbon after the reaction. This could be attributed to a lower dispersion and agglomeration of the active component during CSMR and was consistent with the lower thermal stability (Table 3) and MSI. The carbon deposition rate decreased for Ni particles larger than 30 nm and was insignificant for particles with a size of 100 nm [67]. The HRTEM data confirmed the results of the XRD and TA. For spent Ni-Pd/CeMg-A-S-V, the sample contained two types of active component: 15-25 nm in size and clusters consisting of several atoms (Figure 9). HAADF-STEM with an EDX analysis showed (Figure 10) that the CeO\({}_{2}\) and MgO regions were present in the samples. These inhomogeneities were due to the complete destruction of the solid solution. Analogous results have been reported by [PERSON] et al. [28], who prepared a (CeMg)\({}_{1-x}\)Ni\({}_{x}\)O\({}_{y}\) catalyst (Ce/MgO = 0.25 - 1) by a polymerized complex method. The combination of the HAADF-STEM images and the STEM-EDX results allowed the identification of the active component phase.