a process for purifying a gas stream containing at least one impurity chosen from the group formed by propane , nitrogen protoxide and ethylene , in which process : the gas stream to be purified is brought into contact with at least one adsorbent including at least one x zeolite containing barium cations ; at least one impurity is adsorbed on the adsorbent . preferably , the adsorbent includes particles of x zeolite exchanged to at least 70 %, preferably at least 89 %, with barium cations , it being possible for the adsorbent to furthermore include a bed of activated alumina particles which is located upstream of the bed of barium - exchanged x zeolite .