K(T)p (3) 1 K(T)p (4) In 2.3. Adsorption calorimetry Calorimetric measurements were performed at a constant temperature of 303 K using a Tian-Calvet type microcalorimeter (Seratam BT2.15) connected to a purpose-made volumetric appa ratus. The sample cell contained 400 mg of the sample, whereas the reference cell was left empty. Before measurements, the zeolite sample in the calorimetric cell was outgassed outside the calorime ter by slowly increasing the temperature (0.5 Kmin-1) under a dynamic vacuum up to 700 K, after which the sample was kept at this temperature and a pressure smaller than 10-4 mbar overnight. After this activation procedure, the cell was placed inside the calorimeter, connected to volumetric apparatus and outgassed to the pressure of 10-6 mbar using a turbo-molecular pump. The co2 gas used (99.995% Linde gas Corp.) was further purified by means of freeze-pump-thaw cycles before dosing it into the cell. co2 dos ing was done via a computer controlled valve following a designed programme. After each dose the system was allowed to equilibrate