Calorimetric measurements of the heat of adsorption of CO2 on zeolites with variable content of mono-and divalent cations lead to common conclusions. High initial heats (up to 120 kJ-md -1 for NaA), generally associated with a slow and activated rate of adsorption, are found for high contents of Na +, Li+ or Ca 2 § They are attributed to a limited number of chemisorption sites (0.3 per cr cage in NaA).Physisorption results in lower heats (25-50 kJ.mol-1). The lowest values are obtained with partially or totally decationized zeolites. Transition metal cations induce frequently weaker interactions than IA or IIA. Finally the stronger the energy of adsorption is, the larger the adsorbed amount is.

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Various contents of Li +, Ni 2+ or Cu z+ were introduced in zeolite NaA by conventional cation exchange. Crystal damages are observed on samples having suffered the lower pH.The heat of adsorption of CO2 and CzI-I4 was determined by isothermal calorimetry. Very high initial heats (100-120 kJ tool -1) are found in NaA as well as in Li + exchanged samples, perhaps due to chemisorption on alkaline cations; they vanish when Ni 2+ or Cu 2+ replaces more than 20% of Na +, in like manner with Co 2+ or Zn 2+. For the adsorption of C2H4, high initial heats are absent in the ease of NaA, but gradually appear when divalent cations are introduced.Apart from these strong initial values, the heats of adsorption present a plateau vs. the adsorbed amount. Abnormal low values at the plateau are indicative of crystal damages.