The full results of the Henry constant calculations are compiled in the Supplementary Information (Table .1 in EXCEL file KH_and_GCMC_results.xslx). Figure illustrates typical trends in Henry constant KH (shown on a logarithmic scale) and in the heat of adsorption qst,sim for five zeolites, two with 10 MR pore systems (MFI, MTT) and three having 12MR pores (EUO, FAU, MOR). In addition to plotting the evolution for CH4-xClx species as a function of the number of Cl atoms, results for N2 are also included. It is clearly visible that the affinity towards all hydrocarbons is higher than for N2 and that the interaction strength increases with increasing number of Cl atoms, which is straightforwardly explained with the contribution of the polarizable Cl atoms to attractive vdW interactions. Among the different zeolites, the variation in affinity also increases: While the KH values for ETH span only one order of magnitude, they extend over three orders of magnitude for PCE. The KH values for N2 fall close together, indicating that the Henry's law selectivities for heavier CEs over N2 will vary widely, as will be shown in more detail in the following subsection. For most zeolite-guest combinations, a close correlation between ln(KH) and qst is apparent. An exception is visible for the heaviest CEs adsorbed in MTT, where the isosteric heat still increases when moving from TCE to PCE, whereas the Henry constant decreases. This can be attributed to the relatively narrow channels of MTT, for which the fraction that is accessible to TCE is significantly larger than for the more voluminous PCE molecule. Henry's law selectivities Table .2 of the supplementary EXCEL file contains Henry's law selectivities for a) ETH and CEs over N2, b) CEs over ETH, and c) trans-1,2-DCE over the other DCE isomers. Focus in this discussion will be placed on the selectivities for VC, TCE, and PCE over N2, which are compiled in Figure . For VC, a number of zeolites show selectivities on the order of 500 to 950, with EUO and TON being most selective. Among the four zeolites that are commercially available in high-silica form (MFI, BEA, FAU, and MOR), MFI exhibits the highest selectivity.