The previous simulations were carried out based on a nickel content of 5 wt.-%, which is used to parameterize the reaction kinetics. However, industrially relevant catalysts usually use much higher nickel loadings (typical example: BASF Catalyst G1-85 with > 50 wt.-% Ni/support and tablet size ≥ 3 mm), which probably causes diffusion limitations even at smaller pellet sizes. In order to simulate such more realistic catalyst formulations, the activity is increased by a factor of 10 and the diameter is set to a typically value of 3 mm. The temperature of 556 K was selected as used for validation, while all other parameters are used as stated in table for small pellets. shows the simulated CH4 formation rates and CO reactant selectivity as a function of the CO/COx ratio. The CH4 formation rate shows a flat course similar to the observation for the 800 μm pellets with lower activity, which indicates an effect of internal diffusion. The values in the range of 15 to 20 mmol kg - 1 s -1 are 30 to 50 % higher compared to the lower activity catalysts (10 to 15 mmol kg -1 s -1 , see figure ), which is far less than the activity factor of 10. Hence the higher activity used in the simulations is not fully utilized, which points at severe diffusion limitations. The CO reactant selectivity is even lower than for the 800 μm pellets (see figure ), which underlines that diffusion limitations lead to effective hydrogenation of both carbon oxides within CO/CO2 mixtures. These observations indicate that reactant selectivity might be tailored by adjusting intrinsic activity and selectivity together with internal diffusion limitations.