Atomically detailed simulations were used to present the first information about the performance of isostructural metal organic frameworks (MOFs) having different metal sites, CPO-27-M (M = Ni, Co), as adsorbents and membranes for separation of CH4/H-2 mixtures. Adsorption isotherms and diffusion coefficients of both single components and CH4/H-2 mixtures were computed, and this data was used to predict adsorption selectivity, diffusion selectivity, ideal selectivity, and membrane selectivity of CPO materials at various pressures and feed compositions. Separation performance of CPO materials was compared with other MOFs such as IRMOF-1, -8, -10, -14 and with well-known nanoporous materials, such as zeolites MFI, LTA, and CHA and carbon nanotubes. Results showed that CPO materials exhibit higher adsorption selectivity and membrane selectivity than IRMOFs. These results give insight into the physical properties of MOFs that will be desirable in tuning the structure of MOFs for specific gas separations.