Dealumination of USY zeolites by thermal treatment (part 2) effect of H2O in the atmosphere

The effect of H2O in the atmosphere on the dealumination of USY zeolite by thermal treatment was studied by Si-29-MASNMR,Xe-129-NMR spectroscopy, H-1- MASNMR, XPS and XRD. Structural analysis of two samples, which were prepare d by thermal dealumination of USY zeolite and had equal unit cell parameter , showed that the mechanism of dealumination by thermal treatment varies wi th the presence of H2O in the atmosphere. The thermal treatment in an atmos phere containing H2O resulted in the formation of hydroxyl nests resulting from the removal of framework Al and replacement by Si from amorphous SiO2, and migration of the extra-framework Al to outer surface of the zeolite cr ystallites. And smaller crystallites were associated with a greater degree of dealumination. On the other hand, thermal treatment in an atmosphere not containing H2O resulted in smaller crystallites and more irregular arrange ment of the supercages due to a greater increase in the hydroxyl nests. And it is suggested that cationic extra-framework Al generated by dealuminatio n remain in the crystallites.