## 3 Results and Discussion
### Catalytic Performance
Three various kinds of active phase could be clearly identified: low-dispersed particles with a size of 15-25 nm, which corresponded to metallic Ni; then, the second type of bimetallic NiPd nanoparticles with a size of \(<\)10 nm (Figure 11); and finally, clusters located in the structure of MgO indicating the formation of a Ni-Mg-O solution (Figure 9) after the calcination step. Pd doping affects metal dispersion at two stages of the catalyst synthesis. Firstly, Pd acted as a nucleus for the reduction and growth of Ni particles in the polyol method. The three phases were identified in the XRD pattern for Ni\({}_{0.97}\)Pd\({}_{0.03}\) colloid calcined at 300 \({}^{\circ}\)C in vacuum at 10 mbar: an unidentified phase with interplanar spacings of  
Figure 8: X-ray diffraction patterns of 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. 7.96, 4.07, and 2.61 with an average CSR size of 1.5 nm, the Ni\({}_{3}\)C phase (PDF #04-0853) with a particle size of 14 to 17 nm, and a NiPd alloy (ICSD, CC = 670, 625) with an alloy particle size of 4 nm (Figure S9). Secondly, Pd stabilized the surface structure of active ensembles during the reduction treatment and the CSMR process. Note that the monometallic catalyst prepared from the nickel colloid showed an unexpectedly low activity and stability. Figure 10: EDX mapping of the (**a**,**b**) spent Ni-Pd/CeMg-A-S-V catalysts, (**c**,**d**) C elemental map. Figure 9: (**a**,**b**) HRTEM and (**c**) TEM images of the spent Ni-Pd/CeMg-A-S-V catalysts. Carbon deposits were found on the surface of low-dispersed nickel metal particles. No carbon deposits were found on Ni clusters in the MgO site and/or on NiPd nanoparticles (Figure 10). Ni particles formed as a result of such a reductive partial extraction of Ni\({}^{2+}\) ions in a solid solution will have a fairly strong interaction with the NiO-MgO support and a strength in sintering resistance and coke generation [37; 68]. The size of nickel crystallites impacted the quantity and nature of carbon deposition. A higher metal-support interface prevents the carbon formation or promotes the combustion of carbon from the catalyst surface due to an increased oxygen migration from the substrate to the metal surface [67]. Moreover, alloying Ni with noble metals or the very close location of the noble metal to the active Ni species is an effective way to increase catalytic stability due to breaking the C-H bond in such a way that carbon deposition is reduced [69]. From these images, it can be concluded that the highly dispersed NiPd particles and the Ni clusters in MgO provided a high resistance of the catalyst to sintering and the forming of carbon. Even if the particles were covered by carbon, the stability and activity of this catalyst were excellent, indicating that highly dispersed Ni and NiPd particles were responsible for the catalytic performance. It would be expected that catalysts with a lower nickel content would be efficient for the reaction. Note that doping with Mg improved their thermostability at sintering and magnified the Ni-support interaction. On the other hand, the tolerance to carbon deposits was enhanced for CeO\({}_{2}\)-based catalysts without doping, compared to Ce\({}_{0.2}\)Mg\({}_{0.7}\)Ni\({}_{0.1}\)O\({}_{1.2}\), which can be associated with a decrease in the oxygen mobility at a higher concentration of dopant [28]. Experiments concerning CeO\({}_{2}\)-MgO with an optimal amount of Mg are in progress to develop more effective catalysts. The Ni-Pd/CeMg-A-S-V catalyst had a higher dispersion which prevented the formation of carbon, a lower rate of particle sintering, and a higher concentration of defective oxygen. From the point of view of catalytic properties, the Ni-Pd/CeMg-A-S-V catalyst was most effective among the catalysts prepared, as a result of its proper physicochemical properties.