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Diffusion and adsorption of CO 2 /N 2 mixtures in the zeolitic imidazolate framework ZIF-8 are investigated by molecular dynamics (MD) and Gibbs ensemble Monte Carlo (GEMC) simulations. Structural changes called "gate opening" could be found for the adsorbed single-component gases and for the mixture. The gate opening appears for the mixture at a total number of guest molecules per cavity between that for the pure CO 2 and that for the pure N 2 but closer to that of N 2 which is lower. Due to the stronger dependence of CO 2 adsorption upon the temperature in comparison with N 2 , the adsorption selectivity is predicted to be higher at lower temperatures, which is in accordance with experimental findings.

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A high selectivity of NO x over N2 (simulating air) is found in silico when studying the adsorption of the ternary mixture N2O4/NO2/N2 on the metal–organic framework MIL-127­(Fe) by molecular simulations under consideration of the recombination reaction N2O4 ↔ 2NO2. The number of N atoms in nitrogen oxides NO x and that in N2 is used to define a selectivity of the combined adsorption and chemical recombination that can reach values of about 1000.

Adsorption and diffusion of the gas mixture H2/CH4 in the metal–organic framework (MOF) of structure type zeolitic imidazolate framework-90 (ZIF-90) are revisited. While the adsorption can successfully be examined in Gibbs ensemble Monte Carlo (GEMC) simulations using the common approximation of a rigid lattice, the dynamics of methane in ZIF-90 is remarkably influenced by the lattice flexibility. Molecular dynamics (MD) simulations not only show a strong influence of the lattice flexibility on the diffusion of methane but even find a slight structural phase transition of the lattice. This structural change appeared at higher temperatures and was not caused by the content of guest molecules like in most former discoveries of gate opening. For prediction of mixed gas ZIF-90 membrane selectivity, the adsorption and diffusion results show that the high CH4 adsorption selectivity is overcompensated by the high H2 mobility. The comparison of our results for the H2/CH4 membrane selectivity with experimental findings from mixed gas permeation through supported ZIF-90 membranes shows better agreement than other simulations that use a rigid lattice for MD. Also, the increase of the membrane selectivity by increased temperature could be found.

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