Effect of alkaline modification of products of thermal vacuum and hydrothermal treatment of NH4Na-Y zeolite according to the IR spectral data

The effect of alkaline modification on the structure of the products of heat treatment of NH₄Na-Y zeolite (53% NH ₄ ⁺ , Si/Al - 2.37) in a vacuum at 573 K and in water vapors at 873 K was investigated with the IR spectrum of vibrations of the zeolite framework in the 400–1200 cm^–1 region. It was shown that the high-frequency shift of the bands in the spectra of the products obtained, the stretching vibration of v_as(TO₄) tetrahedrons in particular (T=Si, Al) at 1023 cm^–1 by 6 and 19 cm^–1, is determined by a decrease in the excess negative charge of the framework due to weakening and hydrolytic splitting of Al-O bonds of the deammoniated units with the formation of bridging Si-O(H)...Al and terminal Si-OHHO-Al hydroxyl groups. Treatment of these samples with an aqueous solution of KOH (pH 13.4) at 293 and 353 K restores the normal framework Si-O-Al bonds at the sites of formation of bridging and terminal hydroxyl groups. In the second case, restoration is hindered by substitution of H⁺ by K⁺ with some silanol groups.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. I. V. Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, 199164 St. Petersburg. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1733–1739, August, 1992.