# Nickel-Based Structured Catalysts for Indirect Internal Reforming of Methane
## 3 Results and Discussion
### Temperature Programmed Reduction (H\({}_{2}\)-TPR)  
The H\({}_{2}\)-TPR profiles from room temperature to 800 \({}^{\circ}\)C of NiCrAl foam (profile a), Ni-SmDC powder (profile b). and Ni-SmDC/NiCrAl structured catalyst (profile c) are reported in Figure 5. The corresponding H\({}_{2}\) consumptions amounts (mmol-g\({}^{-1}\)) are reported in Table 3.  
Figure 4: Raman spectra of (a) NiCrAl foam and (b) Ni-SmDC/NiCrAl structured catalyst. Figure 5: Temperature programmed reduction (TPR-H2) profiles: (a) NiCrAl foam, (b) Ni-SmDC powder, (c) Ni-SmDC/NiCrAl structured catalyst. \begin{table}
\begin{tabular}{c c} \hline \hline
**Sample** & **H\({}_{2}\)-Consumption** \\  & **(mmol g\({}^{-1}\))** \\ \hline NiCrAl & 0.11 \\ Ni-SmDC & 1.33 \\ Ni-SmDC/NiCrAl & 0.36 \\  & 1.20 (*) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Consumed hydrogen up to 800 \({}^{\circ}\)C.  
The H\({}_{2}\)-TPR profile of NiCrAl foam (profile a) shows three peaks at 372, 523, and 685 \({}^{\circ}\)C, due to the reduction of the passivated surface. As shown by FIB-SEM and Raman characterizations, and according to literature [39; 40], the high temperature oxidation of NiCrAl alloy produces a layer of different oxides, such as \(\alpha\)-Al\({}_{2}\)O\({}_{3}\), Cr\({}_{2}\)O\({}_{3}\), NiCr\({}_{2}\)O\({}_{4}\) spinel, and trace of NiO. The weak peak at 372 \({}^{\circ}\)C corresponds to the hexavalent chromium reduction to Cr\({}^{3+}\), while the narrow and more intense peak at 523 \({}^{\circ}\)C may be ascribed to Cr\({}^{3+}\)\(\rightarrow\) Cr\({}^{2+}\) reduction of Cr\({}_{2}\)O\({}_{3}\)[50; 51; 52] and NiCr\({}_{2}\)O\({}_{4}\)[53]. The broad peak at 685 \({}^{\circ}\)C can be assigned to the reduction of Ni\({}^{2+}\) to Ni\({}^{0}\) of NiO interacting with Cr\({}_{2}\)O\({}_{3}\)[54] and/or into NiCr\({}_{2}\)O\({}_{4}\) spinel oxide [53], overlapped to Cr\({}^{3+}\)\(\rightarrow\)Cr\({}^{2+}\) reduction into the bulk [55]. The total H\({}_{2}\) consumption of NiCrAl foam was quite small (0.11 mmol g\({}^{-1}\)), confirming that the oxides were present only on a very thin surface layer. The H\({}_{2}\)-TPR of Ni-SmDC powder (profile b) shows a weak peak at 285 \({}^{\circ}\)C, two intense and overlapped peaks at 375 and 440 \({}^{\circ}\)C, and a subsequent H\({}_{2}\) consumption increase up to 800 \({}^{\circ}\)C. In agreement with literature [29; 56; 57], the weak peak at 285 \({}^{\circ}\)C corresponds to the reduction of O\({}_{2}\) chemisorbed (i.e., \(O_{2}^{2-}\)) on the vacancies formed by Sm\({}^{3+}\) doping but also, in a small fraction, into Ni-O-Ce solid solution. The intense peaks at 375 and 440 \({}^{\circ}\)C correspond to the reduction of NiO particles differently interacting with the support and to the contribution of Ce\({}^{4+}\)\(\rightarrow\)Ce\({}^{3+}\) reduction of the surface grains. The final and incomplete H\({}_{2}\) consumption was due to the diffusion-limited reduction of bulk Ce\({}^{4+}\)[58]. The experimental hydrogen consumption was 1.33 mmol g\({}^{-1}\). This value was larger than the hydrogen amount for Ni\({}^{2+}\)\(\rightarrow\)Ni\({}^{0}\) reduction 0.78 mmol g\({}^{-1}\); thus, the excess of hydrogen consumption corresponded to the 18.2% of Ce\({}^{4+}\)\(\rightarrow\)Ce\({}^{3+}\) reduction. The TPR profile of Ni-SmDC/NiCrAl structured catalyst (profile c) is an overlapping of profiles (a) and (b), corresponding to the reduction of NiCrAl foam and Ni-SmDC catalyst. The peak at 326 \({}^{\circ}\)C can be assigned to the reduction of chemisorbed oxygen species and Ni\({}^{2+}\) ions incorporated into the ceria lattice of the Ni-SmDC, superimposed to the initial Cr\({}^{6+}\)\(\rightarrow\)Cr\({}^{3+}\) reduction of Cr\({}_{2}\)O\({}_{3}\) formed on the surface of NiCrAl alloy. Well-defined peaks at 388 and 455 \({}^{\circ}\)C were due to the reduction of NiO particles with weak and strong interaction with the Ce\({}_{0.85}\)Sm\({}_{0.15}\)O\({}_{2-\delta}\) support, overlapped to the complete Cr\({}^{6+}\)\(\rightarrow\)Cr\({}^{3+}\) reduction.