Method of purifying a gas stream containing, apart from carbon dioxide at least one impurity including hydrocarbons and nitrogen oxides, and possibly water, characterized in that it consists in: A bringing the gas stream to be purified into contact with at least one adsorbent in aggregated form either comprising at least 70%, preferably at least 80% and advantageously at least 85%, by weight of zeolite LSX, the crystals of which have a number-average diameter measured by SEM and counting, of less than or equal to 4 μm, at least 90%, preferably at least 95% and advantageously at least 98% of the exchangeable sites of which are occupied by sodium ions, the rest of the cations possibly being, for example, potassium cations, up to 5% by weight of a binder that is inert to the adsorption, and possibly up to 25%, preferably up to 20% and advantageously up to 15% of one or more other zeolites, such as zeolite X, zeolite A, etc. (type A aggregate); or comprising at least 70%, preferably at least 80% and advantageously at least 85%, by weight of a blend of at least 20% and preferably at least 30% of zeolite X and of at most 80%, preferably at least 70%, by weight of zeolite LSX, the crystals of which have a number-average diameter measured by SEM and counting, of less than or equal to 4 μm, at least 90%, preferably at least 95% and advantageously at least 98% of the exchangeable sites of the said zeolites X and LSX of which are occupied by sodium ions, the rest of the cations possibly being, for example, potassium cations, up to 5% by weight of a binder that is inert to the adsorption, and possibly up to 25%, preferably up to 20% and advantageously up to 15% of one or more other zeolites, such as zeolite A, etc. (type B aggregate); B- adsorbing at least some of the carbon dioxide, and at least some of the hydrocarbons and/or N x O y on the said adsorbent; C- desorbing the impurities adsorbed on the said adsorbent; and D- regenerating the adsorbent. A bringing the gas stream to be purified into contact with at least one adsorbent in aggregated form either comprising at least 70%, preferably at least 80% and advantageously at least 85%, by weight of zeolite LSX, the crystals of which have a number-average diameter measured by SEM and counting, of less than or equal to 4 μm, at least 90%, preferably at least 95% and advantageously at least 98% of the exchangeable sites of which are occupied by sodium ions, the rest of the cations possibly being, for example, potassium cations, up to 5% by weight of a binder that is inert to the adsorption, and possibly up to 25%, preferably up to 20% and advantageously up to 15% of one or more other zeolites, such as zeolite X, zeolite A, etc. (type A aggregate); or comprising at least 70%, preferably at least 80% and advantageously at least 85%, by weight of a blend of at least 20% and preferably at least 30% of zeolite X and of at most 80%, preferably at least 70%, by weight of zeolite LSX, the crystals of which have a number-average diameter measured by SEM and counting, of less than or equal to 4 μm, at least 90%, preferably at least 95% and advantageously at least 98% of the exchangeable sites of the said zeolites X and LSX of which are occupied by sodium ions, the rest of the cations possibly being, for example, potassium cations, up to 5% by weight of a binder that is inert to the adsorption, and possibly up to 25%, preferably up to 20% and advantageously up to 15% of one or more other zeolites, such as zeolite A, etc. (type B aggregate); either comprising at least 70%, preferably at least 80% and advantageously at least 85%, by weight of zeolite LSX, the crystals of which have a number-average diameter measured by SEM and counting, of less than or equal to 4 μm, at least 90%, preferably at least 95% and advantageously at least 98% of the exchangeable sites of which are occupied by sodium ions, the rest of the cations possibly being, for example, potassium cations, up to 5% by weight of a binder that is inert to the adsorption, and possibly up to 25%, preferably up to 20% and advantageously up to 15% of one or more other zeolites, such as zeolite X, zeolite A, etc. (type A aggregate); or comprising at least 70%, preferably at least 80% and advantageously at least 85%, by weight of a blend of at least 20% and preferably at least 30% of zeolite X and of at most 80%, preferably at least 70%, by weight of zeolite LSX, the crystals of which have a number-average diameter measured by SEM and counting, of less than or equal to 4 μm, at least 90%, preferably at least 95% and advantageously at least 98% of the exchangeable sites of the said zeolites X and LSX of which are occupied by sodium ions, the rest of the cations possibly being, for example, potassium cations, up to 5% by weight of a binder that is inert to the adsorption, and possibly up to 25%, preferably up to 20% and advantageously up to 15% of one or more other zeolites, such as zeolite A, etc. (type B aggregate); B- adsorbing at least some of the carbon dioxide, and at least some of the hydrocarbons and/or N x O y on the said adsorbent; C- desorbing the impurities adsorbed on the said adsorbent; and D- regenerating the adsorbent.