Synthesis, structural characterization and adsorption of FER-type zeolites

Pure phase FER zeolite and siliceous FER zeolite have been synthesized in the systems of tetramethyl ethylene diamine -Na2O-SiO2-Al2O3-H2O3(I),Na2O-K2O-Al2O3-SiO2-H2O-HCO3-CO32-(II) and pyridine-propylamine-HF-SiO2-H2O(III) respectively. All the samples prepared were characterized by chemical composition, SEM, XRD, FT-IR,Si-29 and Al-27 MAS NMR, and TG/DTA methods. Adsorption isotherms of hexane, methanol and water on these samples were measured using super micro-adsorption-electron balance in vacuum. It is found that all the samples are of high-crystallinity, whereas their thermal stability and adsorption property are remarkably varied because of the differences in composition and micro-defects in the structure of these zeolites. Zeolite FER synthesized in system (I) has less stacking faults and perfect framework. Its adsorption capacities of hexane and methanol are in good agreement with calculated values. The temperature of the zeolite structure damage is at 1190 degrees C. Siliceous FER zeolite possesses perfect framework as revealed by FT-IR and high resolution Si-29 MAS NMR spectra. Its adsorption capacities of hexane and methanol were slightly lower than calculated values because of the unit cell contraction. It has high hydrophobic property. The temperature of the zeolite framework collapse is higher than 1300 degrees C. More stacking faults are found in FER zeolite obtained from system (II). Potassium cations in the channels are difficult to be ion exchanged with protons. Its adsorption capacities of hexane and methanol are obviously low, whereas the capacity of water is relatively high. The temperature of the zeolite structure damage is at 1169 degrees C. According to the sorption isotherms, hexane and methanol are adsorbed in the ten-membered ring channel. Methanol molecules can enter the small cage through the eight-membered ring window at high partial pressure. The adsorption of water correlates to Si-OH defect and concentration of cations in the zeolites.