IR study of the peculiarities of the stabilization of the NH4Na-Y zeolite structure during its hydrothermal dealumination

The variations in the structure of deep-level calcinated NH₄Na-Y zeolite (68 % NH₄⁺, Si/Al = 2.56) at 873 K (stage I of the hydrothermal dealumination) as a result of ammonation and subsequent calcination in water vapor at 973 and 1023 K (stageII) were studied using the IR spectra of zeolite framework vibrations. It was shown that ammonation of the product of stageI promotes the formation of linear disiloxane bonds and extra-framework =Al^VI-OH species identified by absorption at 482, 1196 cm^–1, and 524, 612, 829 cm^–1. The ammonation is also accompanied by an increase in the excessive negative framework charge (ENFC), which is manifested in the high-frequency (HF) shift of the bands that have maxima in thev_as(TO₄) region and equals 10 cm^–1, and also by a decrease in the unit cell parameter (a₀) by 0.14 Å. The decrease in both the ENFC anda₀ for the products of stageII, v_as(TO₄) = 10–20 cm^–1 and a₀ = 0.07–0.14 Å, is due to the formation of nonlinear disiloxane bonds and non-framework aluminum hydroxide species identified by the absorption bands at 478, 1173 cm^–1 and 530, 615, 835 cm^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 660–664, April, 1993.