The present invention is directed to a process for separating nitrogen from gas mixtures containing nitrogen and less strongly adsorbed components such as oxygen, hydrogen, argon or helium by use of an at least binary exchanged X-zeolite having lithium and a divalent cation selected from the group consisting of barium, cobalt, copper, chromium, iron, magnesium, manganese, nickel, zinc and mixtures thereof in a ratio of preferably 5% to 50% of the divalent cation and 50% to 95% lithium.