Study of the Influence of Several Mordenite Modifications on Its N2 and O2 Adsorption Properties

Na-mordenite zeolite was cation-exchanged to obtain Li-, Li/Ag- and Ag-mordenite and treated with NH 4 F to obtain Na-, Li-, Li/Ag-mordeniteF (1%) and Na-mordeniteF (10%). Samples were characterized by XRD, nitrogen physisorption, 27 Al and 29 Si MAS NMR, FTIR spectroscopy, and X-ray fluorescence. Special attention was given to the presence of F - ions in the mordenite structure. Equilibrium adsorption isotherms of high-purity components N 2 and O 2 were measured at 298 K. For the cation-exchanged mordenite samples, the adsorbed nitrogen volume is slightly higher than that obtained in other zeolites such as zeolite X with a lower Si/Al ratio. This reveals the significant influence of the cation's accessibility to the gas molecules in these adsorption processes. N 2 adsorption capacity increases in the order Na + < Ag + < Li +, whereas the N 2 /O 2 adsorption selectivity varies as Na + < Li + < Ag + for the cation-exchanged mordenite samples. In samples prepared by fluorinated treatment, the effect is different depending on the extraframework cation present. When Na + and Li + cations are present, F atoms decrease the shielding caused by the walls to the cation's charge resulting in an increase on the adsorption selectivity, especially at low pressures, with a slight decrease in the number of active sites. However, the effect of F on Ag + cations is mainly an electronegative effect, making the adsorbate−adsorbent interaction less favorable.