# Nickel-Based Structured Catalysts for Indirect Internal Reforming of Methane
## 3 Results and Discussion
### Catalytic Activity  
The catalytic test of dry reforming of methane (DRM) was carried out in a fixed-bed quartz reactor using a single and a triple catalytic bed as schematically reported in Figure 6a. The single and triple configurations are named F1 and F3, respectively. The images of F1 and F3 structured catalysts are displayed in Figure 6b. A double layer Ni-SmDC/NiCrAl structured catalyst was chosen for the catalytic tests. The dry reforming of methane reaction was investigated at the pressure of 1.3 bar and in transient conditions of temperature in the range of 800-550 \({}^{\circ}\)C, each 50 \({}^{\circ}\)C. A flow of reactants (100 cm\({}^{3}\)-min\({}^{-1}\)) having the composition CH\({}_{4}\):CO\({}_{2}\):N\({}_{2}\):He = 20:20:10:50 (vol %) was fed into the reactor with a gas hourly space velocity (GHSV) of 94,000 h\({}^{-1}\) for F1 and 31,000 h\({}^{-1}\) related for F3. A preliminary investigation (not reported) showed that the uncoated foam was not catalytically active under the present experimental conditions. The effect of GHSV and reaction temperature on the catalytic activity of F1 and F3 are discussed. Figure 7 shows the CH\({}_{4}\) and CO\({}_{2}\) conversion (%) as a function of temperature (a), the corresponding H\({}_{2}\)/CO molar ratio vs. temperature (b) and the H\({}_{2}\)/CO molar ratio as a function of CO\({}_{2}\) conversion (%) (c). The reaction conditions are: CH\({}_{4}\)/CO\({}_{2}\) = 1, P = 1.3 bar, GHSV = 94,000 h\({}^{-1}\) for F1, GHSV = 31,000 h\({}^{-1}\) for F3. The equilibrium conversion curves are also added as dashed lines. As expected by the strong endothermicity of the DRM reaction, the reactants' conversions were promoted by increasing temperature (Figure 7a). The GHSV of F1 (94,000 h\({}^{-1}\)) was significantly high and the CH\({}_{4}\) conversion was quite low going from 6% at 550 \({}^{\circ}\)C to 59% at 800 \({}^{\circ}\)C, which is well below the thermodynamic value (93% at 800 \({}^{\circ}\)C). Moreover, at all investigated temperatures, the CO\({}_{2}\) conversion was much higher than that of CH\({}_{4}\), reaching a maximum of 73% at 800 \({}^{\circ}\)C. As already reported in literature [29; 60; 61], if the mass transfer limitation effect is negligible, the DRM is better promoted at low GHSV. Indeed, using three structured catalysts (F3), the GHSV decreased to 31,000 h\({}^{-1}\) and the CH\({}_{4}\) conversion markedly increased going from 10% at 550 \({}^{\circ}\)C to a maximum of 87% at 800 \({}^{\circ}\)C, much closer to the equilibrium dashed line. Correspondingly, the conversion of CO\({}_{2}\) was favored over that of CH\({}_{4}\) but the difference between CO\({}_{2}\) and CH\({}_{4}\) was reduced by increasing temperature. At 800 \({}^{\circ}\)C, the CO\({}_{2}\) conversion was 94%, corresponding to the thermodynamic value. The always greater CO\({}_{2}\) conversion, compared to CH\({}_{4}\), was due to the concomitant occurrence of the RWGS reaction Equation (2). Thus, the not-reformed CO\({}_{2}\) was hydrogenated by the produced H\({}_{2}\), forming CO and H\({}_{2}\)O and causing an H\({}_{2}\)/CO molar ratio less than unity in the whole temperature range, as shown in Figure 7b. Figure 6: (**a**) Scheme of reactor loading in a single and triple catalytic bed (**b**) and images of single and triple portion of the structured catalyst Ni-SmDC/NiCrAl, named as F1 (above) and F3 (below). Figure 7: _Cont._  
The H\({}_{2}\)/CO ratio increased towards the thermodynamic value by increasing the temperature and decreasing the GHSV, in agreement with the decreasing difference between CO\({}_{2}\) and CH\({}_{4}\) conversion values of the F3 system compared to F1. Furthermore, as shown in Figure 7c, the H\({}_{2}\)/CO ratio increased linearly with the CO\({}_{2}\) conversion, independently from the GHSV, confirming that the RWGS was kinetically favored over the DRM and close to thermodynamic equilibrium. Figure 8 shows the Arrhenius plot of the reactants' consumption rates for the F1 structured catalyst.