Calorimetric Heats of Adsorption and Adsorption Isotherms. 2. O2, N2, Ar, CO2, CH4, C2H6, and SF6 on NaX, H-ZSM-5, and Na-ZSM-5 Zeolites

Isosteric heats of adsorption and adsorption isotherms have been measured simultaneously in a calorimeter for a series of gases of increasing size and magnitude of quadrupole moment (Ar, O2, N2, CH4, C2H6, SF6, CO2) on adsorbents of varying pore structure and ion type (NaX, H-ZSM-5, Na-ZSM-5). Adsorption isotherms have been checked for reversibility by desorption experiments. The average experimental error in loading is ±0.6%; the average uncertainty in the isosteric heat of adsorption is ±0.5 kJ/mol. Heats of adsorption of nonpolar molecules (CH4, C2H6, SF6) increase in the order NaX, silicalite, H-ZSM-5, Na-ZSM-5 at low coverage. Heats of adsorption of nonpolar molecules are almost identical on silicalite, H-ZSM-5, and Na-ZSM-5 at high coverage. Heats of adsorption of the quadrupolar molecule CO2 increase in the order silicalite, H-ZSM-5, Na-ZSM-5, NaX. The electric field adjacent to Na+ sites is 6.2 V/nm, on the basis of the difference between the heat of adsorption of CO2 in Na-ZSM-5 and the heat of adsorption of CO2 in silicalite.