The adsorption of CO and H-2 on single-metal-atom (Fe, Co, Ni and Cu) embedded graphene (M-G) has been studied using density functional theory calculations. Fe-G and Co-G can capture up to three CO molecules per metal atom strongly, but tend to weakly or not adsorb H-2 molecules. Under standard conditions (298.15 K and 1 bar), they show a high adsorption selectivity ratio for CO over H-2. The density of states analysis reveals that the strong adsorption between CO and Fe(Co)-G results from the hybridization between d states of Fe (Co) and sp states of CO. Our findings suggest that Fe-G and Co-G can be used as a filter membrane for removing CO efficiently in the feed gas of hydrogen fuel cells. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.