Multi-walled carbon nanotubes containing oxygenated groups (O-MWCNTs) have been functionalized with ammonia to improve the adsorption capacity and selectivity of CO2/CH4 in gas adsorption process. The effects of oxygen and nitrogen containing functional groups (e.g. hydroxyl and amine), on CO2 and CH4 adsorption were studied. The ideal adsorption capacities of MWCNTs were determined using volumetric method at ambient temperature and moderate pressures (from 0.1 to 3.0 MPa). The MWCNTs containing nitrogen groups (N-MWCNTs) showed much higher adsorption capacity of CO2 and selectivity of CO2/CH4 against the O-MWCNTs at different pressures. The highest selectivity was observed at lower pressures at 298 K for the N-MWCNTs. The dynamic adsorption experiments were carried out with a feed containing one to fivefold of CO2 to CH4 in a packed bed of N-MWCNTs at 298 K and atmospheric pressure. The breakthrough curves and breakthrough times of CO2 and CH4 were determined for the mixed gases. The results indicated high efficiency of the prepared N-MWCNTs in dynamic separation of CO2 and CH4. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.