The separation and recovery of the greenhouse gases CHF3 and CHClF(2 )from emissions is essential to avoid adverse environmental effects. Nanoporous carbons are excellent candidates for the capture of CHF3 . However, little research has been done on the effect of pore size on the adsorption capacity and selectivity of CHClF2 over CHF3 in nanoporous carbon materials. The effect of the pore size on the competitive adsorption of a binary CHF3 - CHClF2 mixture in graphitic slit pores has been investigated using a combination of Monte Carlo simulations and breakthrough curve experiments over a wide range of pressures and temperatures. The entropy changes have a considerable effect on selectivity of CHClF2 over CHF3 because the size of the adsorbate molecule is close to the effective height of the pores; conversely, adsorption energy has a significant impact. The selectivity of CHClF2 over CHF 3 at 0.05-1.0 MPa increases in the order 19.47 < 16.62 < 13.20 < 11.77 < 8.30 < 5.17 < 5.67 angstrom. The mechanisms for adsorption and the selectivity of CHClF2 over CHF3 were determined, as were the effects of pore size and pressure on adsorption energy and adsorption entropy. This combination of methods provides an effective strategy for the design and screening of adsorbent materials for CHF3-CHClF2 separation and recovery applications.