MICROPOROUS CHARACTERISTICS OF H-Y, H-ZSM-5 AND H-MORDENITE DEALUMINATED BY CALCINATION

The modifications of the microporous volume of zeolites resulting from thermal dealumination have been examined by measuring the changes in the unit cell parameters as well as the N-2 and n-pentane adsorption isotherms. For the cubic HY and orthorhombic H-ZSM-5 zeolites, the differential decrease of the microporous volume per nonframework aluminum (NFAl) can be predicted by assuming NFAl is concentrated in pores available to N-2. For the orthorhombic H-mordenite, NFAl is homogeneously spread in all pores, available or not to N-2. The Gurvitch rule (volume of adsorbed N-2=volume of adsorbed pentane) is respected in HY and H-ZSM-5, but not in H-mordenite, irrespective of the degree of dealumination.