Abstract
Using IR and29Si NMR spectroscopy the influence of alkaline modification on the structure of samples obtained by steaming the ammoniated form of NH4NaY zeolite (53% NH4+, Si/Al=2.37 pretreated under a moist atmosphere at 873 K) at 973 and 1073 K has been studied. Highly dealuminated forms of faujasite arise in the course of hydrothermal treatment as a result of the transfer of Al from the framework to extraframework hydroxide species accompanied by the formation of silica-type disiloxane bonds. The treatment of highly dealuminated samples with an aqueous solution of KOH at 353 K results in the partial regeneration of the crystallographic positions of Al in the framework. The structure of the sample modified with the alkali is identical to that of silicaalumina gel (Si/Al ≈ 2.2) “aged” in air for a long period of time.
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