COMPARATIVE FT INFRARED STUDY OF STRUCTURAL-CHANGES OCCURRING ON DEALUMINATION OF ZEOLITE NA-Y WITH ETHYLENEDIAMINETETRAACETIC OR HYDROCHLORIC-ACID

IR lattice vibration spectra were used to monitor the changes in the s tructure of zeolite Na-Y upon its dealumination with ethylenediaminete traacetic acid (EDTA) or with HCl. The terminal =Si-O(H,Na) bonds thus formed (which are detectable by characteristic absorbance at nu 900-9 50 cm(-1)) are energetically less uniform when EDTA has been used as t he dealuminating agent. This inhomogeneity is connected with the local deformations of zeolite structure which result in lowering the symmet ry of silicon-oxygen tetrahedra. As a consequence, two novel bands app ear at nu 1090 cm(-1) and 1200 cm(-1) in addition to the fundamental a bsorption bands, nu(as) (TO4) (T = Si, Al), at 1030 cm(-1) and 1145 cm (-1). A mechanism of dealumination is proposed, which takes into accou nt the topochemical peculiarities involved in the chelation of the fra mework aluminum ions with EDTA.