On a technical scale, the methanation reactions are catalyzed by a solid catalyst, for which nickel is most frequently used as active material, due to high activity and selectivity . The active compound is typically supported on porous solid substrates, such as Al2O3 pellets, and introduced into the reactor. Most commonly, fixed-bed reactors are applied in industrial scale, but fluidized-bed and slurry-bubble-columnreactors are also considered . The advantages of the latter reactors are that small catalyst pellets are used, which reduces diffusion limitations within the porous pellets and hence high effective reaction rates are expected. However, diffusion limitations are not necessarily problematic, but can even improve the productivity in Langmuir-Hinshelwood reactions, as Roberts and Satterfield have already shown back in the 60s . Though that study focuses on generic hydrogenation reactions the conditions investigated can probably be applied to methanation, as well. In addition, Zimmermann et al. report egg-yolk catalyst pellets for methanation of CO2 with optimized heat and mass transfer limitations in order to control the dynamic behavior of fixed-bed methanation reactors. Hence, the selection of the pellet size represents a crucial step in the process design, since it is not limited to the conventional compromise between pressure loss and effective reaction rate.