Structural changes of Y zeolites during ion exchange treatment: effects of Si/Al ratio of the starting NaY

The effects of Si/Al. ratio of starting NaY zeolites on structural changes during ion exchange treatments were studied. Three zeolites of different SUM ratio were subjected to three cycles of ion exchange treatment using (NH4)(2)SO4 and subsequent calcinations, and analyzed after each cycle. In the first ion exchange, the structural changes of the zeolites were almost independent of the Si/Al ratio of the starting NaY zeolites. For all three zeolites, about 60% of Na ions were exchanged, and the relative crystallinity decreased to about 80% of the starting NaY. In the second and third ion exchanges, the structural changes depended on the Si/Al ratio of the starting NaY zeolites. The zeolitic framework of Y zeolite with a low Si/Al ratio of 2.4 deteriorated, whereas Y zeolite with a medium Si/Al ratio of 2.8 and Y zeolite with a high Si/Al ratio of 4.1 retained their high crystallinity even after the third ion exchange. Furthermore, among the three zeolites, Y zeolite with a medium Si/Al ratio of 2.8 showed largest degrees of ion exchange, dealumination, and mesopore formation. (C) 2003 Elsevier Science Inc. All rights reserved.