# Nickel-Based Structured Catalysts for Indirect Internal Reforming of Methane
## 3 Results and Discussion
### Catalytic Activity
The natural logarithm of the consumption rates linearly depends on the inverse of temperature \(\frac{1}{T}\) between 550 and 700 \({}^{\circ}\)C, confirming that the reaction operates in a kinetic regime and, in agreement with the above discussion, the CO\({}_{2}\) consumption rates are always greater than those of CH\({}_{4}\). The corresponding apparent activation energies, proportional to the slope of the straight lines, were equal to E\({}_{\text{CO}_{2}}\) = 64.8 kJ mol\({}^{-1}\) and E\({}_{\text{CH}_{4}}\) = 79.3 kJ mol\({}^{-1}\), respectively. These values were in good agreement with those previously obtained for the Ni-SmDC powder [29], suggesting that the coating process over the NiCrAl foam did not significantly alter the kinetics of the DRM reaction. Figure 7: (**a**) CH\({}_{4}\) and CO\({}_{2}\) conversion (%) as a function of temperature, (**b**) the corresponding H\({}_{2}\)/CO molar ratio, (**c**) H\({}_{2}\)/CO molar ratio as a function of CO\({}_{2}\) conversion (%). Reaction conditions: CH\({}_{4}\)/CO\({}_{2}\) = 1, P = 1.3 bar, GHSV = 94,000 h\({}^{-1}\) (F1), GHSV = 31,000 h\({}^{-1}\) (F3). Equilibrium conversion is also indicated with the dashed line. To verify the integration of the structured catalyst in IIR-SOFC configuration, the F3 catalytic system was studied in four daily start-up and shut-down operation (DSS) operations. According to the literature, in such condition a quick damage of the reforming system may occur [62; 63]. The temperatures examined between 550 and 800 \({}^{\circ}\)C lasted a total of 20 h. The CH\({}_{4}\) and CO\({}_{2}\) conversion and the H\({}_{2}\)/CO ratio are shown in Figure S2, and the values at the representative temperatures of 700, 750, and 800 \({}^{\circ}\)C are reported in Table 4. The F3 system was particularly stable at all investigated temperatures and a decrease in performance was not observed. On the contrary, conversions and the H\({}_{2}\)/CO ratio tended to increase; for example, at the low temperature of 700 \({}^{\circ}\)C the CH\({}_{4}\) conversion increased from 55.2% up to 63.4%. The main reason for the catalyst deactivation during DRM is recognized in the loss of Ni active sites due to carbon deposition [8; 64; 65], especially during low temperature operation [66; 67]. Therefore, a morphologic analysis of spent catalysts was performed to investigate the eventual carbon formation. SEM micrographs of the three portions of F3 used catalyst, named F3\({}_{\text{inlet}}\), F3\({}_{\text{medium}}\), and F3\({}_{\text{outlet}}\), are reported in Figure 9. For each portion, high (on the top) and low (on the bottom), magnification images are displayed. The high magnification micrographs reveal the presence of deposited carbon filaments and the low magnification images show cracks on the Ni-SmDC coating layer distributed all over the porous structured foam. From F3\({}_{\text{inlet}}\) to F3\({}_{\text{outlet}}\) the amount and thickness of carbon filament decreased, and the number of cracks was also reduced. Specifically, the carbon content measured by EDX analysis dropped from 17, 14, and 2 wt.% from the F3\({}_{\text{inlet}}\), F3\({}_{\text{medium}}\), and F3\({}_{\text{outlet}}\) portions, respectively. This feature was likely due to the higher methane partial pressure and the lower operating temperatures at the inlet of the catalytic bed in comparison to the outlet [68]. Thus, in the inlet portion of the catalyst (F3\({}_{\text{inlet}}\)), the side reactions were most favored, causing more carbon formation, cracks, and few detachments as well.