The potentialities in the use of bio-chars prepared by steam assisted slow pyrolysis as adsorbents of gases of strategic interest (ca. N2, CO2, CH4) and their mixtures were explored. The bio-chars prepared from Populus nigra wood and cellulose fibers exhibited a narrow microporosity with average pore sizes ranging between 0.55 and 0.6 nm. The micropore volume increased with the pyrolysis temperature, allowing CO2 and CH4 uptakes at room temperature between 1.5-2.5 mmol/g and 0.1-0.5 mmol/g, respectively. These values are in line with those from the literature on biomass derived carbon-based materials exhibiting much higher porous features than those herein reported. As for the separation of CO2/N2 and CO2/CH4 gas mixtures, data showed that the prepared bio-chars exhibited good selectivities for CO2 over both N2 and CH4: between ca. 34 and 119 for a CO2/N2 mixture in typical post-combustion conditions (15/85, v/v) and between 14 and 34 for a CO2/CH4 mixture typical of natural gas upgrading (30/70, v/v).