Compared to MIL-101(Fe)-NH₂, MIL-101(Cr)-NH₂ has considerably higher adsorption of CO₂. On the other hand, the adsorption of CH₄ and N₂ by MIL-101(Cr)-NH₂ is lower than the adsorption of these gases by MIL-101(Fe)-NH₂ leading to a higher selectivity of CO₂ to CH₄ and N₂ for MIL-101(Cr)-NH₂. The chemisorption mechanism is more influential in higher temperatures and pressure, which can be attributed to the performance of amines which can adsorb more CO₂ at higher temperatures and pressure. The isosteric heat of CO₂ adsorption on MIL-101(Cr)-NH₂ was estimated equal to − 31 kJ mol^-1.MIL-101(Cr)-NH₂ was synthesized and characterized by the BET, XRD, FESEM, TGA, and DTA methods. The BET surface area of the synthesized MOF was achieved equal to 1768 m² g^-1. The adsorption capacity of pure CO₂, CH₄, and N₂ was estimated using the volumetric method. A new three-parameter equation was presented to model the experimental adsorption data including both types I and II isotherm shapes. Using the Ideal Adsorbed Solution Theory (IAST), the selectivity of CO₂ to CH₄ at high pressure, and CO₂ to N₂ at lower pressures was estimated equal to 4.1 and 4.7, respectively. In addition to 25 °C, the adsorption tests were performed at 18 and 30 °C to estimate the adsorption heat of CO₂ on MIL-101(Cr)-NH₂ achieved equal to − 31 kJ mol^-1. The adsorption isotherm of CO₂ at 25 and 30 °C have been almost identical showing the role of the chemisorption mechanism of CO₂ by the amine functional group, especially at higher temperatures and pressures. Furthermore, the resistance of synthesized MOF to water was investigated by putting it in contact with water for 24 h. The result showed that MIL-101(Cr)-NH₂ can be classified as thermodynamically stable to water.