Contribution to the study of framework modification of SAPO-34 and SAPO-37upon water adsorption by thermogravimetry

The adsorption-desorption of water vapor in SAPO-34 and SAPO-37 is followed in isobar conditions (P-H2O = 17.6 mbar) by thermogravimetry at temperatur es from 20 degrees C to 400 degrees C. The phenomenon is reversible in SAPO -34 but not in SAPO-37. The rise in water uptake is the highest at around 6 0-70 degrees C, i.e. in range where an attack of the frameworks was previou sly reported, The reversibility (or not) of water adsorption-desorption upt ake is linked to this reversible (or not) framework modification. The kinet ics of desorption in SAPO-34 is strongly slowed down between 40 degrees C a nd 60 degrees C. This suggests that the full restructuration of the framewo rk requires some time (700 min in the experimental conditions used). The mo rphology of the crystals of the two SAPOs is unchanged upon hydration but t emplate-free SAPO-34 crystals become progressively destroyed in the electro n beam of an electron microscope. (C) 1999 Elsevier Science B.V. All rights reserved.