The validity of the model is evaluated by simulating experimental conditions not used for parameterization of the tortuosity (excl. at 556 K, 175 and 800 μm pellet size, variable 𝑧 values). The effective methane formation rate Δ𝑛̇C H 4 is chosen as criterion for validation, according to the parametrization approach in equation . Figure shows the respective results of simulation and experiment for small (175 µm) and large (800 µm) catalyst pellets at temperatures between 513 and 573 K and CO/CO2 ratios of 0 ≤ 𝑧 ≤ 1.