It can be seen that an increase in temperature leads to an increase in the methanation rate, which is expected from Arrhenius law and underlines the absence of limitations by chemical equilibrium. All profiles exhibit similar methanation rates for the hydrogenation of pure CO2 (𝑧 = 0) and pure CO (𝑧 = 1), while a maximum is found for the hydrogenation of CO/CO2 mixtures. This maximum is more pronounced and located at higher CO2 concentrations for the 175 µm catalyst pellets compared to their 800 µm counterparts. Furthermore, the effective reaction rate is lower for the larger pellets, which specifically holds for high CO2 contents and high temperatures. These pellet size effects will be discussed in detail in the next section. The comparison between simulation and experiment generally exhibit small deviations only. Hence, the validity of the model can be confirmed in principle. Notably, the kinetic parameters have been fitted to experimental data obtained for the 175 µm particles at 556 K. Extrapolation to other temperatures was performed without adaption of any temperature-dependent parameter, such as the activation energies. The extrapolation to larger particles was done by fitting the tortuosity only, as described in sec. 2.2.4. Hence, the good agreement between simulations and experiment clearly points at the absence of significant internal or external mass transfer limitations of the 175 µm particles. However, a certain deviation between simulation and experiment is observed for small pellets at high temperatures (𝑇 = 556 K; 573 K) and small CO content in the feed (𝑧 = 0.05 -0.2). For detailed analysis of this deviation, the spatial profiles within the porous catalyst pellet are displayed in figure for the case of maximum deviation (𝑧 = 0.0924; 𝑇 = 573 K). Figure shows the simulated spatial profiles of the molar fractions, which exhibit almost no gradient for N2, H2 and CO2 at the external catalyst surface, while a small gradient is observed for CH4 and H2O. For CO, in contrast, the low molar fraction leads to a drop towards zero inside the pellet, even though the gradient is small, as well. In addition, the CO molar fraction declines from 𝑧 = 0.0924 at the reactor inlet to 𝑧 R = 0.0433 at the outlet, which indicates a significant CO conversion (𝑋 CO ≈ 56 %). The validation of the simulation results by measuring the profiles inside the catalyst pellet would be highly desirable, but to the best of our knowledge this has only been performed for pure CO oxidation into CO2 as simple model reaction so far .