IR study of the peculiarities of alkaline realumination of the highly dealuminated product of hydrothermal treatment of zeolite Y

Abstract

The effect of alkaline modification on the structure of highly dealuminated zeolite Y, prepared by steaming (at 973 K) the ammoniation product of NH4-Y zeolite (53% NH4+, Si/Al=2.37) pretreated at 873 K in a humid atmosphere, was studied by means of IR spectra of the zeolite lattice vibrations. Treatment of the sample with 0.25 N KOH at 293 K causes the dissolution of the non-framework aluminum hydroxide species with formation of basic aluminate, and the cleavage of linear siloxane bridges at the dealuminated sites. At 353 K the cleavage involves the non-linear disiloxane bonds, while the interaction of potassium aluminate with the terminal ≡Si-O(H,K) bonds thus formed brings about the regeneration of normal Al-O-Si bridges; however, parallel amorphization of the zeolite structure takes place due to pronounced depolymerization of the high-siliceous framework.