Since the experiments are performed as previously described in detail in Meyer et al. , only a short summary is given here. The 5 wt.-% Ni/Al2O3 catalyst used is prepared via the incipient wetness impregnation method of 800 µm Al2O3 pellets (Puralox® Al2O3-Spheres 0.8/160, Sasol Germany) and characterized by N2 physisorption and H2 chemisorption experiments, which reveal an average pore size of 8 nm, a Ni crystallite size of 7.5 nm and metal surface area of 3.7 m 2 g -1 . For determination of the pellet size effect the as-made catalyst is also crushed and sieved to a fraction of 150-200 µm sized pellets (denoted as 175 µm pellets). All experiments are performed using a stainless-steel reactor with an inner diameter of 4.5 mm and operated in fixed-bed mode. For providing an equal bed length of ca. The total inlet molar fraction of COx (CO and CO2) is constant at 0.1, while the ratio between CO and CO2 is varied in the range of 0 ≤ 𝑧 ≤ 1 in the experiments according to the definition in equation .