In this work, the grand canonical Monte Carlo method was employed to study the adsorption and separation characteristics of CH 4 /H 2 on MOF-5 and five zeolitic imidazolate frameworks (ZIFs), including two sodalite (SOD), ZIF-8 and -67, two merlinoite (MER), ZIF-10 and -60, and one DFT, ZIF-3. Simulations show that more CH 4 molecules are adsorbed in all frameworks than H 2 , which is consistent with a higher pure gas isosteric heat of adsorption of CH 4 as compared with that of H 2 . For both gases, adsorbed amounts primarily rely on the physical and chemical parameters of the adsorbent. Results of density distribution profiles and equilibrium snapshots of the ZIFs indicate that the most preferential gas adsorption sites for both CH 4 and H 2 are the positions near linkers. At high pressures, CH 4 begins to fill up in the center of the SOD cage. We also found that the selectivity for CH 4 increased with the difference between the isosteric heats of adsorption of CH 4 and H 2 , ∆q st , but decreased to some extent due to the packing effect. Both the isosteric heats of adsorption and the packing effect are mainly influenced by the topology of the framework.

Separation of important chemical feedstocks, such as C 2 H 6 from natural gas, can greatly benefit the petrochemical industry. In this paper, the grand canonical Monte Carlo method has been used to study the adsorption and separation of CH 4 and C 2 H 6 in zeolites, isoreticular metal-organic framework-1 (IRMOF-1) and zeolitic imidazolate frameworks (ZIFs) with different topology, including soadlite, gmelinite and RHO topologies. Compared with mordenite zeolite and IRMOF-1, ZIFs and mordenite framework inverted (MFI) zeolite have better separation performance for C 2 H 6 /CH 4 mixtures at different mole fractions of C 2 H 6 . From the study of equilibrium snapshots and density distribution profiles, adsorption sites could be grouped as (1) sites with strong interactions with adsorbent and (2) sites with strong interactions with surrounding adsorbates. The gas molecules occupied the first site and then went on to occupy the second site. In CH 4 /C 2 H 6 mixture adsorption/separation, the adsorption of CH 4 was confined by the existence of C 2 H 6 . Due to energetic effect, C 2 H 6 selectivity was affected by temperature at a low-pressure range, but did not change as much in a high-pressure range because of packing effect in micropore. In binary adsorption, large C 2 H 6 molecules favour sites with strong adsorbent interactions. At high pressures, packing effects played an important role and it became easy for small CH 4 molecules to access the sites with strong adsorbate interactions.

b S Supporting Information ' INTRODUCTIONThe storage and separation of important gases, such as H 2 , N 2 , CH 4 , and CO 2 , is a challenging research field, due to the impending energy crisis and related global pollution that are dramatic issues today. A range of approaches have been explored to utilize materials of different property and construction. Metal organic frameworks (MOFs) 1,2 and zeolitic imidazolate frameworks (ZIFs) 3-5 are new classes of microporous materials with potential applications in adsorption separations, catalysis, and gas storage. Because the property of flexibility promises to be particularly important in gas adsorption, the preparation of microporous organic polymers with permanent microporosity and high surface areas, such as covalent organic frameworks (COFs), 6,7 polymers of intrinsic microporosity (PIM), 8,9 porous aromatic framework (PAF), 10,11 hypercrosslinked polymers (HCPs), 12,13 crystalline triazine-based organic frameworks (CTFs), 14 and conjugated microporous polymers (CMPs), 15,16 is currently of intense interest. Additionally, study of microporous organic molecular crystals (MOMCs) is an emerging area of interest. [17][18][19][20][21][22] The microporous crystal of tris(o-phenylenedioxy)-cyclotriphosphazene (TPP) is one of the examples that has been discussed the most among the MOMCs. [20][21][22][23][24][25] Very recently, McKeown and his co-workers 26 discovered a MOMC, as displayed in Figure 1, formed by 3,3 0 ,4,4 0 -tetra-(trimethylsilylethynyl)biphenyl (TTB). Figure 1 c and d showed the attractive structural feature of the TTB crystal of threedimensional interconnectivity of the void space. It allows multiple paths for the adsorbents to access each micropore and avoids potential reduction of adsorption because of pore blocking. The three-dimensional interconnectivity of microporosity is expected to enhance the kinetics of adsorption in comparison with crystals of one-dimensional channels of a similar size. They found that the crystals of TTB can capture a significant amount of H 2 or N 2 at 77 K.In this work, a combination of classical and quantum calculations is performed to investigate the adsorption and separation of some critical gases (including H 2 , N 2 , CH 4 , and CO 2 ) in crystal TTB. We first used grand canonical Monte Carlo (GCMC) to simulate pure-component adsorption of H 2 , N 2 , CH 4 , and CO 2 in TTB crystal and verify the model with available experiments. Binary mixture simulations were then performed for adsorption of N 2 , CH 4 , or CO 2 over H 2 at 50% mixtures, and adsorption selectivities were calculated. Furthermore, first-principle calculations were performed to scan the potential energy surface of small molecules moving along the channel, and the most stable adsorption configurations were investigated. ' COMPUTATIONAL DETAILSWe adopted a multiscale theoretical method to predict the gas adsorption in crystal TTB. In the classical simulation, the force field parameters for the interaction between H 2 and the TTB were fitted by the calculat...

Grand canonical Monte Carlo simulations were employed to investigate the adsorption and separation of C2H6, CO2 and CH4 on two zeolitic imidazolate frameworks (ZIF-2 and ZIF-71). The adsorption isotherm and isosteric heat of pure gas, the separation performance of C2H6-CH4, CO2-CH4 and C2H6-CO2 binary mixtures and C2H6-CO2-CH4 ternary mixtures on two ZIFs were simulated and discussed. For single component gas adsorption at a low pressure, the adsorption amount depended on isosteric heat; at a high pressure, due to the limited pore volume, ZIFs preferably adsorbed smaller size gas molecules. For gas mixture separation, energetic effect dominated at low pressure, therefore, ZIFs selectively adsorbed gas component with strong interactions; packing effect usually played an important role at high pressures, consequently, smaller size component would be more entropically favorable. Results demonstrated that both ZIF-2 and ZIF-71 were of good separation performance for these three binary mixtures. For the ternary mixture separation, it was found that ZIF-2 cowld effectively separate C2H6 and CO2 from CH4 at 3000-4000 kPa and room temperature.