Although it is possible to compare the gas release curves of krypton in MFU-4 with the release curves of xenon in MFU-4, and the gas release curves of krypton in MFU-4-Br with the release curves of xenon in MFU-4-Br, it is not straightforward to compare the results of MFU-4 with MFU-4-Br. Since the gas release is a diffusion process, the size of the MOF crystals matters (as we reported recently on an example of ZIF-8 of various sizes loaded with SF6 ) and thus, since both samples are not identical in their particle size, their gas release curves should not be directly compared. Therefore, in order to compare both MOF systems with each other, the activation energy barrier of the guest release was determined both experimentally and computationally. The activation energy barrier of the guest release was determined experimentally by carrying out modulated thermogravimetric analysis (MTGA TM by TA instruments). Modulated TGA uses an oscillation temperature program to obtain kinetic parameters during mass loss. Herein the studies revealed that activation of xenon release from MFU-4 and MFU-4-Br was ca. 67 ± 1 and 92 ± 2 kJ•mol -1 , respectively, while the activation energy of krypton release from MFU-4-Br was ca. 75 ± 4 kJ•mol -1 (Table , Fig. ). Since the release of krypton from MFU-4 occurs relatively rapidly already at ambient temperature, an alternative approach for determining the activation energy had to be utilized. We measured gas release curves from -100 to 300 °C at different heating rates (1, 3, 5, and 7 K•min⁻¹) (Fig. ) and used these data to determine the activation energy (Fig. ), which was approximately 53 ± 9 kJ•mol⁻¹. The determined values of activation energy are in good agreement with the guest-pore aperture size ratio (Table ) following the ordering of Kr/MFU-4 < Xe/MFU-4 < Kr/MFU-4-Br < Xe/MFU-4-Br. Furthermore, the activation energy of the herein studied systems was compared to previously reported values for other systems (Table ). Figure illustrates the relationship between the activation energy and the guest-pore aperture size ratio, serving as a useful tool to predict properties of other systems in terms of effective gas trapping.