SELECTIVE REMOVAL OF SILICON FROM ZEOLITE FRAMEWORKS USING SODIUM-CARBONATE

The mild treatment of various zeolites (X, Y and ZSM-5) with sodium carbonate in aqueous solutions has been investigated. The removal of silicon from highly siliceous zeolites led to a significant decrease of the Si:Al ratio, mostly with the ZSM-5 and Y zeolites. However, the original structure, surface area and size of the micropores were essentially preserved, although healing processes did occur after silicon removal from the framework. All the aluminium atoms remained in the tetrahedral configuration during the treatment, which, therefore, provides a novel means for significantly increasing the ion-exchange capacity or the density of protonic sites of the zeolites studied.