Metal-organic frameworks (MOFs) with open metal sites have attracted lots of attention because of their high binding energy for adsorbates. MIL-100(Cr) is one of the potential MOFs for challenging separations. Multicomponent breakthrough studies on MOF pellets are critically needed because only pelletized adsorbents can be used in pressure or temperature swing adsorption processes. Thus, in this study, we compared the adsorption equilibrium of MIL-100(Cr) powder and pellets and carried out a breakthrough study of multicomponent gas mixtures on pelletized MIL-100(Cr), which revealed interesting effects of activation conditions on its performance. The experimental results show that the CO2 adsorption capacity of MIL-100(Cr) powder activated at 523 K and high vacuum (10-10 bar) was about 2.5 times higher than that of MIL-100(Cr) treated under mild activation conditions (423 K). The highest 5.8 mol/g CO2 capacity at 298 K and 1 bar is consistent with the high CO2-Cr3+ binding energy of 63 kJ/mol, determined using density functional theory calculations. However, the number drops to 4.05 mol/g for pelletized samples. The negative impact of densification on the adsorption capacity follows the order of CO2 > N-2 > CH4 for MIL-100(Cr)250 and CH4 > N-2 > CO2 for MIL-100(Cr)150, which also suggests that the effects of open Cr sites on the adsorption capacity follows the order of CO, > N-2 > CH4 on MIL-100(Cr). The selectivity of MIL-100(Cr) pellets based on breakthrough measurements for CO2/N-2 (20/80) and CO2/CH4 (40/60) mixtures was 4.3 and 10.7, respectively.