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 zeoli te (68 % NH4+, Si/Al = 2.56) at 873 K (stage I of the hydrothermal dea lumination) as a result of ammonation and subsequent calcination in wa ter vapor at 973 and 1023 K (stage II) were studied using the IR spect ra of zeolite framework vibrations. It was shown that ammonation of th e product of stage I promotes the formation of linear disiloxane bonds and extra-framework = Al(VI)-OH species identified by absorption at 4 82, 1196 cm-1, and 524, 612, 829 cm-1. The ammonation is also accompan ied 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 the v(as)(TO4) region and equals 10 cm-1, and also by a decrease in the unit cell parameter (a0) by 0.14 angstrom. The decre ase in both the ENFC and a0 for the products of stage II, DELTAv(as)(T O4) = 10-20 cm-1 and DELTAa0 = 0.07-0.14 angstrom, is due to the forma tion of nonlinear disiloxane bonds and non-framework aluminum hydroxid e species identified by the absorption bands at 478, 1173 cm-1 and 530 , 615, 835 cm-1.